Social Psychology

F. Cultural Diversity: Disgust

Psychological Factors

We discussed how senses transform Most people are disgusted by cockroaches. But, what if
Would you eat physical energy into impulses, you were offered a glass of juice that just
a cockroach? which become sensations and had a sterilized cockroach dipped in it?
then perceptions. However, If the thought “EWWW!” just crossed
your perceptions are usually influenced by psychologi- your mind, you have helped us dem-
cal factors, such as learning, emotion, and motivation. onstrate that when something repul-
If offered a cockroach to eat, most of us would react sive (cockroach) touches something
with great disgust. e facial expression to express pleasant (juice), it contaminates or
disgust (right photo) is similar across cultures. infects the pleasant object, even if it is
Disgust is triggered by the presence of a variety of con- unchanged (remember, the cockroach
taminated or offensive things, including foods, body prod- Tongue contains sensors is harmless as it had been sterilized).
(taste buds) for five tastes. You still feel disgust (Rozin, 2007).
ucts, and gore. We show disgust, which is a universally

recognized facial expression, by closing the eyes, narrowing the nostrils, Disgust is considered a basic emotion, and people around the

curling the lips downward, and sometimes sticking out the tongue world express disgust in the same way (Rozin et al., 2000). How- Photo Credits: top, © Gustavo Andrade/Photolibrary; bottom left, © Malcolm S. Kirk; bottom right, © Danielle Pellegrini/Photo Researchers, Inc.; bottom center,
(above photo). ever, cultural factors influence what we perceive to be disgusting. © Guy Mary-Rousseliere

Cultural Factors

Your particular culture has a strong influence on which foods you learn to perceive as disgusting and which you think are delicious. We’ll
describe some foods that are considered delicious in some cultures and disgusting in others.

Plump Grubs Fish Eyes and Whale Fat Milk and Blood

For most U.S. citizens, eating a round, so , Although some Americans have developed a taste Several tribes in East Africa
white worm would be totally unthinkable. for raw fish (sushi), a common dish in Japan, most supplement their diet with
For the Asmat of New Guinea, however, a would certainly gag at the thought of eating raw fresh blood that is some-
favorite delicacy is a plump, white, 2-inch fish eyes. Yet for some Inuit (Eskimo) children, times mixed with milk.
larva—the beetle grub. e natives harvest raw fish eyes are like candy. Here you see a young They obtain the blood by
dozens of the grubs, put them on bamboo girl using the Inuits’ all-purpose knife to gouge puncturing a cow’s jugular
slivers, and roast them. A photographer out the eye of an already-filleted Arctic fish. vein with a sharp arrow. A
from the United States who did a story on cow can be bled many times
the Asmat tried to eat a roasted grub, but Eskimos also hunt a type of whale (the nar- and suffer no ill effects. e
his American tastes would not let him whal) that provides much of their protein. They blood-milk drink is a rich
swallow it (Kirk, 1972). consider the layer of fat under the skin (mukluk) source of protein and iron.
a delicacy, and they eat it raw or dried.

Cultural Influences on Disgust variety of noncontaminated foods (cat, dog, or horse meat) or for
e reaction of U.S. college students to eating white, plump grubs certain situations (touching a dead person) (Rozin et al., 2000). e
fact that the same things are viewed as all right in one culture but
or cold, glassy fish eyes or having a warm drink of blood mixed as disgusting in another graphically shows how much cultural
with milk is almost always disgust. Researchers believe that show- values can influence and bias perceptions.
ing disgust originally evolved to signal rejection of potentially con-
taminated or dangerous foods. Today, however, because of cultural Just as psychological factors are involved in perceiving taste,
and psychological influences, we may show disgust for eating a they are also involved in experiencing pain.

110 M O D U L E 5 S E N S A T I O N

G. Research Focus: Mind over Body?

Definitions One of the truly amazing research Research Methods
findings is how sugar pills or placebos e procedure used to separate a person’s expectations (placebo effect)
Can sugar can somehow “trick” us into feeling or from the effects of a pill or medical treatment is called double-blind.
pills reduce
In a double-blind procedure, neither the researchers (“blind”) nor the sub-

pain? getting better. For example, because jects (“blind”) know who is receiving what treatment. Because neither research-

many of us believe that we will be ers nor subjects know who is receiving which treatment, the researchers’ or
helped by taking pills, about one-third of the population subjects’ expectations have a chance to equally affect both treatments (drug
report feeling much better or having less pain a er taking a and placebo).
pill, not knowing that it was only a sugar pill—a placebo. For example, in a double-blind design, headache sufferers would be
A placebo is some intervention, such as told they will be given one of two kinds of pills to decrease

taking a pill, receiving an injection, or pain. Unknown to the subjects (“blind”) and the

undergoing an operation, that resembles researchers (“blind”), one of the pills is a drug and one

medical therapy but that, in fact, has no is a placebo. If subjects taking the drug report the same

medical effects. decrease in pain as those taking the placebo, researchers

A placebo effect is a change in the conclude the drug is no better than a placebo. If subjects

patient’s illness (for better or worse) that Only a double-blind procedure can tell taking the drug report less pain than those taking the
is due to the patient’s beliefs or expecta- if a treatment is real or a placebo. placebo, researchers conclude the drug is medically useful
tions rather than the medical treatment. because it is better than a placebo.

One of the strongest and most studied placebo effects is Over the past 25 years, hundreds of double-blind experiments have
the ability for placebos to relieve pain (G. A. Hoffman et al., found that 30 to 98% of people have reported beneficial effects after
2005). For example, if people take a pill for headache pain and taking placebos (Talbot, 2000). For example, 85% of patients reported
believe or expect that the pill will decrease their pain, about a reduction in pain from Herpes simplex (cold sores and genital sores)
30 to 60% of people will actually feel less pain a er taking a a er a placebo drug treatment. Also, 98% of patients reported marked or
placebo (Talbot, 2000). complete relief of pain from ulcers a er placebo treatment (Turner et al.,
Because the placebo effect can occur a er taking any pill 1994). ere are hundreds of other examples that are just as incredible!
(injection or medical procedure), researchers needed to find a What follows is a research study that examines whether the cost of
method that could separate a person’s expectations and beliefs a treatment influences its effectiveness—another possible placebo effect.
from the actual effects of a new drug or medical treatment. is promises to be interesting . . . let’s learn what the researchers found.

Power of Pricing Conclusion: Mind over Body!
Is a cheaper pill less effective Based on the results of decades of research, three major conclusions about
Is a more than a more expensive one? placebos have been reached (Ariely, 2008; Niemi, 2009; Talbot, 2000).
expensive Do we believe that a higher First, potentially powerful placebo effects, such as reducing pain or speed-

pill better? price translates into higher ing recovery from medical procedures, have been underestimated.
quality, and if we do, can our Second, both medication and fake surgeries can produce significant placebo
belief or expectation effects, such as reducing pain, in 30 to 98% of
make the drug more patients.
effective? Logic should ird, placebos indicate a powerful mind-
tell us that the price of a over-body interaction, which explains why
pill does not determine its level of effectiveness. people may experience health benefits
Researchers examined this fascinating question from taking placebos.
and their results may surprise you. Researchers asked Placebos may work by creating posi-
participants to rate pain caused by electric shocks tive expectations and beliefs that reduce
applied to their wrist, before and a er taking a new anxiety and stress. In turn, the reduction
painkiller. Half of the participants were told the new of anxiety and stress results in perceiving
pill costs 10 cents, and half were told it costs $2.50. less pain and improves immune system
In fact, all participants received a placebo. Results functioning, so the body makes a quicker
showed 85% of those using the expensive pill felt less recovery (W. A. Brown, 1997). us, there is
pain, compared to 61% using the cheaper pill. us, no question our minds have powerful effects
the pricier the pill, the higher the expectation of its on our bodies! In fact, doctors are so aware of Placebos work because of
effectiveness, and the stronger the placebo effect (Ari- the power of placebos that 45% of them have the power of our mind.

ely, 2008; Waber et al., 2008). prescribed a placebo to their patients (Sherman & Hickner, 2008).
Next we review three major conclusions about Next, we’ll examine pain in more detail and see how mental factors can
placebos. affect the perception of pain.

G . R E S E A R C H F O C U S : M I N D O V E R B O D Y ? 111

H. Pain

Definition

What All of us can relate to pain because at one time involved in pain perception are religious beliefs and whether the
or another we have felt various degrees of pain. harm was caused intentionally. For instance, practicing Catholics
causes pain? Pain is an unpleasant sensory and emotional perceive electric shocks as less painful when looking at an image
of the Virgin Mary (Wiech et al., 2008). Other research finds
experience that may result from tissue damage, that people who believe they are receiving an electric shock from

one’s thoughts or beliefs, or environmental stressors. another person on purpose, as opposed to accidentally,
rate the same shock as more painful (K. Gray & Wegner,
Pain receptors send nerve impulses to the somatosen- 2008). ese studies show that the psychological expe-
sory and limbic areas of the brain, where impulses are riences of pain are different even when the physical
changed into pain sensations. Pain is essential for sur- sensations are the same!
vival: It warns us to avoid or escape dangerous situa- Research also finds placebo treatments can
tions and makes us take time to recover from injury. result in a lower perception of pain. For example,
The definition of pain differs from the other after men had hot metal plates placed on their
senses in three ways. First, pain results from many hands, they were given an injection of either a
different stimuli (physical injury, psychological and painkiller or a placebo (they did not know which—
social stressors), whereas the other senses respond double-blind procedure). Brain scans showed that
primarily to a single stimulus. Second, pain’s inten- the placebo injections that had reduced pain acti-
sity depends not only on the physical stimulus but
also on social and psychological factors. ird, the vated pain-reducing brain circuits similar to the circuits activated
treatment of pain depends not only on treating any physical injury by real painkillers (Petrovic et al., 2002; Ploghaus et al., 2003).
but also on reducing emotional distress that may have caused or
contributed to the painful sensations (Kerns, 2006, 2007). is and other studies demonstrate how one’s beliefs can activate
Researchers recognize pain is a complex process that may or circuits in the brain that, in turn, result in changes in perception
may not include tissue damage and usually involves social, psy- (decreased pain) (Erdmann, 2008; Scott et al., 2007).
chological, and emotional factors, which can cause, increase, or
decrease painful sensations (Innes, 2005; Nicholson & Martelli, Other psychological factors, such as changes in attention, can also
2004). Examples of social, psychological, and emotional factors alter perception of pain and answer an interesting question: Why do
headaches come and go, depending on what you are doing?

Gate Control Theory

How does Although a headache is painful, the
pain may come and go as you shi
the mind your attention or become absorbed
2. With gate PAIN 2. With gate NO
stop pain? in some project. is phenomenon open, we feel open closed, we PAIN
is explained by the gate control pain. feel no pain.

theory of pain (Melzack & Katz, 2004). Gate Gate closed

The gate control theory of pain says that nonpainful nerve

impulses (shifting attention) compete with pain impulses (head-

ache) in trying to reach the brain.

is competition creates a bottleneck, or neural gate, 1. Pain signals 1. Pain signals
that limits the number of impulses that can be transmit- coming from coming from
ted. us, shi ing one’s attention or rubbing an injured spinal cord spinal cord do
area may increase the passage of nonpainful impulses reach the brain. not reach the brain.
and thereby decrease the passage of painful impulses; as
a result, the sensation of pain is dulled. e neural gate from a painful ankle from reaching his brain and thus prevented feelings Photo Credit: Digital Stock Corporation
isn’t a physical structure but rather refers to the competi- of pain (right figure above: NO PAIN). Later, when the game was over, the
tion between nonpainful and painful impulses as they quarterback’s attentional and emotional states calmed down, the neural gates
try to reach the brain. opened, impulses from his broken ankle reached his brain, and he felt lots of
pain (le figure above: PAIN). is same process explains why you may not
e gate control theory explains how a professional notice the pain from your headache when involved in another activity.
football quarterback was able to play the last six min-
utes of an important football game with a broken ankle Pain: Physical and Psychological
(Associated Press, 2002). The gate control theory says According to the gate control theory, your perception of pain depends not
that the football player’s intense attentional and emo- only on a stressful mental state or physical injury but also on a variety of
tional involvement in the game caused his brain to send psychological, emotional, and social factors, which can either decrease or
nonpainful impulses that closed neural gates in the increase your perception of pain (Pincus & Morley, 2001).
spinal cord. The closed neural gates blocked impulses
Your perception of pain from a serious injury can also be reduced by your
brain’s ability to secrete its own pain-reducing chemicals, called endorphins.

112 M O D U L E 5 S E N S A T I O N

Endorphins Dread Dread seems to be connected to
Someone who has experienced a serious injury—in foot- the pain centers of the brain.
Does the brain ball, for example—will usually report that initially the How is
make its own pain was bearable but with time the pain became much
dread related One study placed participants
painkillers? worse. One reason pain seems less intense immediately to pain? into a brain scanner (fMRI) and
a er injury is that the brain produces endorphins.
offered them the choice of
Endorphins (en-DOOR-fins) are chemicals produced by the brain and secreted in receiving a stronger shock now or a weaker shock in

response to injury or severe physical or psychological stress. the future. Some participants dreaded the shock so

e pain-reducing properties of endorphins much that they chose to receive the stronger shock
are similar to those of morphine, a powerful instead of waiting to receive a weaker one. Brain
painkilling drug (Ropper & Samuels, 2009). imaging of these “extreme-dreaders” showed height-
e brain produces endorphins in situations ened activity in the brain’s pain cen-
that evoke great fear, anxiety, stress, or bodily ter. Thus, dread is not simply an I want my
injury, as well as a er intense aerobic activity. emotional response to fear or anxiety; root canal

now!

For example, subjects with severe jaw pain rather, a significant component of
produced increased levels of endorphins a er dread involves devoting attention
they received a placebo injection, and subjects Brain releases endorphins in times to the expected and unpleasant
who reported the greatest pain relief showed of great pain, stress, or fear. physical threat (in this case shock)

the greatest endorphin release (Zubieta et al., 2005). In other research, patients (Berns et al., 2006). ese results
showed increased levels of endorphins a er bandages were removed from badly suggest that when it comes to
burned areas of their bodies or a er nerves of their teeth were touched (Szy- getting root canal surgery or
felbein et al., 1985). Overall, there is a strong relationship between an increase receiving a painful shot, it is not
in endorphin release and a decrease in pain perception (Zubieta, 2007). ese the actual procedure people dread most, but rather
studies indicate that the brain produces endorphins to reduce pain during times the waiting time (Blakeslee, 2006b).
of intense physical stress. Next, we’ll learn how having thin needles inserted
Next, we’ll look at the connection between dread and your brain’s pain center. into your body can help reduce pain.

Acupuncture Initially, scientists trained in the rigor- Studies on the effectiveness of acupuncture in reducing back pain
ous methods of the West (in particular, indicate that almost 50% of patients report long-term improvement
Photo Credits: left, © AP Images/Aaron Harris; right, © PhotoDisc, Inc.; bottom, © Royalty-Free/Masterfile Can an ancient the United States) expressed doubt (6 months) a er acupuncture treatment (Haake et al., 2007). Acupunc-
technique about an ancient Chinese pain-reducing ture has been shown to relieve some kinds of pain (back and knee pain,

reduce pain?

procedure, called acupuncture. dental treatment) and nausea (from chemotherapy or morning sick-
Acupuncture is a procedure in which a trained practitioner inserts ness), but there is no persuasive evidence that it is effective in other
thin needles into various points on the body’s surface and then manu- conditions, such as headache or drug addiction (Aamodt & Wang,
ally twirls or electrically stimulates the needles. 2008; Comarow, 2008; Hall, 2008).

After 10–20 minutes of needle stimula- One interesting study examined the impact of a placebo
tion, patients o en report a reduction in pain. treatment (fake acupuncture treatment) by applying equal
e mysterious part of this procedure is the amounts of heat to people’s right and le arms. Research-
points of insertion—such as those shown in ers then told participants they were being given acupunc-
the photograph on the right—were mapped ture treatment on their right arm, but what participants
thousands of years ago and, as researchers didn’t know is the treatment was a sham. People reported
now know, are often far removed from the feeling less pain in their right arms than in their le arms
sites of injury. even though equally intense heat was applied to both arms
Today, modern scientists have explained (Kong et al., 2006). is study suggests that the power of
some of the mystery surrounding acupunc- people’s belief in acupuncture is strong enough to change
ture. First, the points of needle insertion, their perception of pain.
which seem unrelated to the points of injury, Acupuncture is effective for Many researchers insist it doesn’t matter where needles
are o en close to known pathways that con- nausea, headaches, and some
duct pain. Second, there is some evidence that are placed or that needles are used at all; the only thing that
kinds of pain. matters, they say, is that a person believes he or she is get-

stimulation of these points causes secretion of endorphins, ting real acupuncture. Furthermore, the stronger their belief, the better
which we know can reduce pain (Hall, 2008; Kemmer, 2007). the results (Hall, 2008; Madsen et al., 2009; Price et al., 2008).
For example, if patients are first given a drug that blocks secre- Next, we turn to a very practical question: Can a sense be replaced
tion of endorphins, acupuncture does not reduce pain. ird, if it is damaged? Of the five major senses—vision, audition, taste, olfac-
fMRI brain scans showed that acupuncture decreases neural tion, and touch—damage to vision and audition is especially disastrous
activity in brain areas involved in pain sensations (Aamodt & to the quality of life. As such, researchers are trying to develop artificial
Wang, 2008; Ulett, 2003). eyes and ears.

H . P A I N 113

I. Application: Artificial Senses

Artificial Visual System

Is an e cause and degree of blindness depend on which part of the visual system is affected. For example, a person
artificial eye would be totally blind if the photoreceptors (rods and cones) in the retina were destroyed (retinitis pigmentosa, an
inherited disease) or if the entire retina or optic nerve were damaged. First, we’ll look at a microchip that could be
possible? implanted into the retina to replace photoreceptors damaged by disease.

Artificial photoreceptors. At the beginning of this module, we Image not available due 1. Terry scans surroundings with
told you about Terry, who was completely blind. In Terry’s to copyright restrictions a glasses-mounted camera.
case, he was blind because the photoreceptors (rods and 2. Data travel from the glasses
cones) in his retina were damaged by a genetic disease. For through a wire behind his ear to a Photo Credit: © AP Images/Stephen Chernin
individuals like Terry who have problems with their photo- microcomputer to get processed. Figure/Text Credit: (top) Illustration based on K. Daniel Clark from “Newsfronts: Science & Technology,” by Dawn Stover, Popular Science, August 1997, p. 29.
receptors, researchers have developed a microchip the size 3. Processed data go to a Reprinted by permission.
of a match head that is implanted in the back of the retina. wireless transmitter and then to a
receiver implanted behind his ear.
is microchip sends impulses that travel on to the brain 4. Data then go to a microchip
for visual processing. Although this microchip does not implanted in his eye. Normal visual
restore full vision, it allows people who are now totally blind processes occur next. Data are
to see rough forms of light, movement, and objects. e illus- transmitted by the optic nerve to
tration to the right shows how this amazing procedure works. the brain’s visual center.

For individuals who are blind because their entire eye or optic Special glasses and eye implants work
nerve is damaged, researchers are developing a complete artificial together to allow Terry to “see.”
eye that would send impulses directly to the brain.

Camera sent electrical Brain implant. In an attempt to restore some vision, a blind patient was fitted with a min-
signals directly to brain. iature camera that sent electrical signals to 100 electrodes that were implanted directly into
the visual cortex, located in the occipital lobe (figure at le ). When activated, the electrodes
stimulated neurons in the visual cortex and produced 100 tiny spots of light. is patient
could see the letter S when some of the 100 electrodes were stimulated (LaFee, 2000).
Although the 100 electrodes in this patient’s visual cortex provided more visual informa-
tion than did Terry’s 16, neither patient was able to see the outlines of objects or walk
around without using a cane.

However, recently, researchers made a significant step forward in developing an artificial
visual system.

Functional vision. e major goal in developing an artificial visual system is to provide enough visual
information so a blind person has meaningful visual function, such as reading letters and avoiding
objects while walking around a room. Researchers are getting closer to reaching this goal.
Jerry, a 62-year-old man who has been blind since the age of 36, volunteered to have electrodes
implanted into his brain’s visual cortex (right photo). Jerry wears a pair of glasses that, on one side,
holds a tiny camera and, on the other side, an ultrasonic range finder. e range finder analyzes echoes
from high-frequency sounds (beyond our range of hearing) that provide information on location, size,
and distance of objects. e tiny camera provides visual information that is like looking through a
tunnel opening about 2 inches wide and 8 inches high. Both devices send electrical signals to a small
computer Jerry wears on his hip. In turn, the computer analyzes and relays electrical information to a Artificial visual system lets Jerry
panel of electrodes that were implanted into and stimulate the visual area in Jerry’s occipital lobe (white “see” a 2-inch-high letter.

cords going into skull) (Dobelle, 2000).
Using this device, Jerry can recognize a 2-inch letter from 5 feet away and avoid large objects as he moves around a room. A er
receiving upgrades to his device over the years, Jerry can navigate the subway system on his own (J. Anderson, 2005). e development
of devices to help provide blind people with functional visual information is advancing. Researchers are now trying to put a tiny camera
inside the eye rather than on eyeglasses, which would allow people to scan their environment by simply moving their eyes, rather than
moving their heads (Humayun, 2008).
Researchers are also developing an artificial cochlea for the inner ear.

114 M O D U L E 5 S E N S A T I O N

Kinds of Deafness
ere are two major kinds of deafness that have different effects, causes, and treatments. e most severe kind of
What causes deafness is caused by damage to the inner ear and is called neural deafness. A less severe kind of deafness is caused
deafness? by problems in the middle ear and is called conduction deafness.

Conduction Deafness Neural Deafness

More than 28 million Americans, almost 10% of the population, Hellen Keller, who was born deaf and blind, said, “To be deaf is a
have hearing loss called conduction deafness (Ruben, 2007). greater affliction than to be blind.” Hellen Keller had neural deafness,
which, unlike conduction deafness, is not helped by hearing aids.
Conduction deafness can be caused by wax in the auditory canal, inju-
ry to the tympanic membrane, or malfunction of the ossicles. All of these Neural deafness can be caused by damage to the auditory receptors
conditions interfere with the transmission of vibrations from the tympanic (hair cells), which prevents the production of impulses, or by damage to the
membrane to the fluid of the cochlea, resulting in degrees of hearing loss.
auditory nerve, which prevents nerve impulses from reaching the brain.
Conduction deafness, occurring in 30–40% of adults over 65, Since neither hair cells nor auditory nerve fibers regenerate, neu-
can o en be treated with a hearing aid, which replaces the function
of the middle ear. Hearing aids pick up sound waves, change them ral deafness was generally untreatable until the development of the
to vibrations, and send them through the skull to the inner ear. cochlear implant. Currently, the only approved treatment for certain
kinds of neural deafness is the cochlear implant described below.
Cochlear Implants

Cochlear implant: Transmitter Receiver 3 Receiver, which is
How it works
implanted in the bony skull,
1 Microphone, which is worn Microphone receives the electrical signals 4 Thin cable is threaded into a
and sends them along a thin uid- lled tube of the cochlea until
wire cable to the cochlea. it makes contact with the auditory
nerve. When the receiver sends
behind the ear, gathers and sends electrical signals through the wire
sound waves to a sound processor. cable, the signals trigger impulses
in the auditory nerve.
2 Sound processor transforms Sound Thin cable Auditory
processor nerve 5 Auditory nerve carries the
sound waves into electrical signals,
which are sent to a tiny transmitter. Outer ear Cochlea “manufactured” impulses to the
auditory areas in the brain, which
Auditory interpret and transform impulses
canal into auditory impulses.

Can deaf If the auditory nerve is intact, a cochlear and lips (speech reading). Many could converse on the telephone
implant (figure above) can be used to treat (B. Stone, 2002; Svirsky et al., 2000).
people hear? neural deafness that is caused by damage to e results are more complicated for children who did not learn
the ear (Ohl & Scheich, 2007). to speak before becoming deaf. Researchers reported that when
The cochlear implant is a miniature electronic device that is surgically cochlear implants were put in before age 3½, deaf children had the
implanted into the cochlea. The cochlear implant changes sound waves best neurological development, while implants a er age 7 resulted
into electrical signals that are fed into the auditory nerve, which carries in the poorest auditory development (Seppa, 2005). at’s because
them to the brain for processing. brains of younger children are more flexible or plastic, which means

As you proceed step by step through the figure above, notice younger brains are better able to develop neurological responses
that the cochlear implant first changes sound waves into electrical to auditory information and learn to hear and speak
signals (1, 2, and 3) and then sends the electrical signals into (Rauschecker & Shannon, 2002). For example, Julia
Photo Credit: © James M. Kubus, Greensburg, PA the auditory nerve (4), which sends impulses to the brain (5). received an implant when she was 2½, and at age 9 she
Worldwide, about 100,000 adults and children with speaks and reads above her age level (Reisler, 2002).
severe neural deafness have received cochlear implants Advances in screening for hearing impairments in
(up from 5,000 in 1990) (Chorost, 2007). e child in newborns have made cochlear implants for infants a
the photo at right, deaf from birth, is reacting to welcomed new trend. Other recent trends include plac-
hearing his first sounds a er receiving a cochlear ing cochlear implants in both ears and implanting in
implant. older adults who no longer benefit from hearing aids
Using the newest cochlear implants (cost up (Brody, 2008a).
to $50,000), adults who had learned to speak As we end this module, notice that we primarily
before becoming deaf could understand about 80% discussed how senses transform energy into electrical
This child, deaf from
birth, reacts after hearing
of sentences without any facial cues and from 90 to with cochlear implant. impulses. Next, in Module 6, we’ll focus on how “mean-
100% of sentences when watching the speaker’s face ingless” sensations turn into meaningful perceptions.

I . A P P L I C A T I O N : A R T I F I C I A L S E N S E S 115

Summary Test

A. Eye: Vision B. Ear: Audition

1. Waves in about the middle of the 7. The stimuli for hearing, or audition, are
electromagnetic spectrum are visible sound waves, which have several physical
because they can be absorbed by the characteristics. The physical characteristic
human eye. These waves make up of amplitude or height of sound waves
the and can be is transformed into the subjective
absorbed by receptors at the back of experience of (a) ,
the eye. which is measured in units called
(b) . The frequency
2. Upon entering the eye, light waves pass first through a curved, of sound waves (cycles per second) is
thin, transparent structure called the (a) , whose transformed into the subjective experi-
function is to bend or focus light waves into a narrower beam. ence of (c) , which for
Next, light waves pass through an opening in the eye called the humans ranges from about 20 to 20,000
(b) . Around this opening is a circular, pigment- cycles per second.
ed muscle called the (c) ; its function is to dilate
or constrict, thus increasing or decreasing the amount of entering 8. The outer ear is composed of a funnel-like shape, called the
light. Finally, light waves pass through a transparent, oval struc- external ear, whose function is to gather (a) .
ture called the (d) , whose function is to further These waves travel down a short tunnel called the
focus light waves precisely on the photosensitive back surface of (b) and strike a thin, taut membrane
the eye, which is called the (e) . called the (c) , whose function is to transform
sound waves into (d) .
3. The retina has several layers of cells, but only the very back
layer contains photoreceptors. The photoreceptors that are used 9. The middle ear has three tiny bones (hammer, anvil, and stir-
to see in dim light and transmit only black, white, and shades rup), which together are called (a) . Vibrations in
of gray are called (a) . Photoreceptors that are the tympanic membrane produce mechanical movements in the
used to see in bright light and transmit colors are called ossicles, the third of which is attached to another thin membrane,
(b) . called the (b) , which is made to vibrate.

4. When rods absorb light waves, a chemical called 10. Of several structures in the inner ear, one is a coiled, fluid-
(a) breaks down and in turn generates tiny filled, tubelike apparatus called the (a) , which
electrical forces that trigger (b) in neighboring contains the auditory receptors, called (b) .
cells. Similarly, when cones absorb light waves, chemicals called Movement of the fluid in the tube causes movement of the
(c) break down and generate tiny electrical forces. basilar membrane, which in turn causes bending of the hair cells,
generating a tiny (c) . If this is large enough,
5. Nerve impulses generated in the eye travel along fibers that it will trigger nerve impulses, which leave the cochlea via the
combine to form the (a) nerve. This nerve carries (d) and travel to the brain.
nerve impulses to an area in the back of each occipital lobe called
the (b) , which transforms impulses into simple 11. Nerve impulses are transformed into rather simple, meaning-
visual (c) , such as lines, shadows, colors, and less auditory sensations when they reach the (a) ,
textures. If the primary visual cortex were totally damaged, the which is located in the temporal lobe. These sensations are trans-
person would be essentially blind. Simple, meaningless sensations formed into meaningful and complete melodies, songs, words, or
are transformed into complete, meaningful images when nerve sentences by the auditory (b) .
impulses reach an area of the brain known as (d) .
12. To tell the direction of a sound, the brain analyzes the differ-
6. We see color because our eyes absorb light waves of different ences in time and intensity between (a) arriving
(a) , which are transformed by the visual system at the left and right ears. The brain determines degrees of loud-
into our experience of seeing colors. One theory of color applies ness by using the (b) of the arriving impulses.
to how the cones function; this is the (b) theory. The discrimination of different tones or pitches is explained by
A second theory of color applies to how the ganglion and thalamic the (c) and theories.
cells function; this is called the (c) theory
of color.

116 M O D U L E 5 S E N S A T I O N

C. Vestibular System: Balance G. Research Focus: Mind over Body?

13. Besides the cochlea, the inner ear contains three arch-shaped, 18. In order to control for the placebo effect,
fluid-filled structures called . The researchers use an experimental design in
movement of fluid in these organs provides signals which neither the researchers nor subjects
that the brain interprets in terms of the move- know who is receiving what treatment.
ment and position of the head and body. The This is the design,
vestibular system is also involved in motion which controls for the expectations of
sickness, Meniere’s disease, and vertigo. both researchers and subjects.

D. Chemical Senses H. Pain

14. Sensors on the tongue respond to five basic tastes: 19. After an injury, you feel two different kinds of pain sensations:
(a) , , , at first, there is sharp, localized pain, which is followed by a duller,
, and . The receptors for taste, more generalized pain. The receptors for
which are called (b) , trigger nerve pain are (a) , which
impulses that travel to the brain, which then trans- send impulses to two areas of the brain,
forms them into the sensations of taste. specifically the (b)
and . If you rub an
15. Volatile airborne substances are drawn into the injured area or become totally absorbed
upper part of the nose, where they dissolve in a thin
film of mucus. Underneath the mucus are layers in another activity, you may experience a
reduction of pain, which is explained by the
of receptors for olfaction (smell), which are (c) . Immediately following a serious
called (a) . These receptors
trigger impulses that travel to an area under- injury or great physical stress, the brain produces pain-reducing
chemicals called (d) .
neath the brain called the (b) .
This area transforms impulses into hundreds of different odors.
I. Application: Artificial Senses
E. Touch
20. There are two basic causes of deafness. If the cause is wax
16. The sense of touch actually provides in the auditory canal, injury to the tympanic membrane, or
information on three different kinds of stimuli: malfunction of the ossicles, it is called
(a) , , and (a) deafness. If the cause
. The various layers of skin Hair is damage to hair cells in the cochlea
follicle or to the auditory nerve, it is called
(b) deafness. One
contain different kinds of touch receptors that treatment for neural deafness is to use a
have different speeds of adaptation. Receptors (c) , which is more effec-
for the sense of touch trigger nerve impulses tive if individuals have learned to speak
that travel to an area in the brain’s parietal before becoming deaf.
lobe, called the (b) . This area
Photo Credit: (#17) © Danielle Pellegrini/Photo Researchers, Inc. transforms impulses into sensations of pressure, temperature, and
pain. The more sensitive the area of the body is to touch, the larger
is its area on the cortex.

F. Cultural Diversity: Disgust Answers: 1. visible spectrum; 2. (a) cornea, (b) pupil, (c) iris, (d) lens,
(e) retina; 3. (a) rods, (b) cones; 4. (a) rhodopsin, (b) impulses, (c) opsins;
17. A universal facial expression that indicates 5. (a) optic, (b) primary visual cortex, (c) sensations, (d) association areas;
rejection of food is called (a) . 6. (a) lengths, (b) trichromatic, (c) opponent-process; 7. (a) loudness,
Besides our innate preferences for sweet and salty (b) decibels, (c) pitch; 8. (a) sound waves, (b) auditory canal, (c) eardrum
foods and avoidance of bitter substances, most of or tympanic membrane, (d) vibrations; 9. (a) ossicles, (b) oval window;
our tastes are (b) and particular 10. (a) cochlea, (b) hair cells, (c) electrical force, (d) auditory nerve;
to our culture. The fact that foods considered fine 11. (a) primary auditory cortex, (b) association areas; 12. (a) sound waves,
in one culture may seem disgusting to people in another culture (b) rate, (c) frequency, place; 13. vestibular organs; 14. (a) bitter, sour, salty,
indicates how much psychological factors influence taste. sweet, umami, (b) taste buds; 15. (a) olfactory cells, (b) primary olfactory
cortex; 16. (a) pressure, temperature, pain, (b) somatosensory cortex;
17. (a) disgust, (b) learned; 18. double-blind; 19. (a) free nerve endings,
(b) somatosensory area, limbic system, (c) gate control theory, (d) endor-
phins; 20. (a) conduction, (b) neural, (c) cochlear implant

S U M M A R Y T E S T 117

Critical Thinking

What Would It Be Like
Never to Feel Pain?

QUESTIONS At the young age of 5, Ashlyn © 2005 Eric Larson/Light of Day, Inc. 5 How helpful would
Blocker has already experienced acupuncture be
1What type of many serious physical injuries. She’s body weight when feeling pain in as a treatment for
research method had a massive abrasion to the cor- their joints, CIPA prevents people people with CIPA?
would you use to nea of her eye, terrible burns, and from sensing this pain and often re-
learn about the life of hundreds of bite marks from fire sults in joint problems. Lack of pain 6 Why is it that
a person who cannot ants. She’s also severely damaged sensitivity can lead to other prob- Ashlyn cannot
feel pain? her tongue, cheek, and lips, knocked lems including bone fractures and sense pain or heat,
out most of her front teeth, and infections. For example, Ashlyn re- but she can feel her
2 What type of neu- crushed her fingers in a door frame. cently had tonsillitis that went unde- parents tickling and
ron is responsible Other children would scream in tected for six months. hugging her?
for people experienc- pain from experiencing any of these
ing pain, heat, and injuries, but Ashlyn never yelled, Despite the daily challenges Ash- ANSWERS
cold? nor did she shed a tear. “I can’t feel lyn faces, she looks like an ordinary TO CRITICAL
my boo-boos,” she says (Tresniowski girl who enjoys doing the same THINKING
3 What is the name et al., 2005). Ashlyn is unique from things others her age do. She likes to QUESTIONS
for the optimum most other children because she swing on the playground and enjoys
state of body arousal cannot feel pain. being tickled and hugged by her par-
Ashlyn cannot achieve ents. Ashlyn is fortunate to have
as a result of not Ashlyn has a rare and incurable support from her parents and school
sweating? Which genetic disorder called CIPA (con- officials to ensure her safety while
areas of our brain and genital insensitivity to pain with an- allowing her to enjoy her childhood.
body help maintain hidrosis). People with CIPA lack pain “There is no reason to think she
this optimum level and temperature sensation, yet have won’t have a normal life,” says Dr.
of arousal? no other sensory deficits. These indi- Lawrence Shapiro, an international-
viduals cannot feel pain and temper- ly recognized child psychologist.
4 How might CIPA ature because they lack nerve fibers Ashlyn’s parents describe her as
affect Ashlyn’s responsible for carrying the sensa- having the “best laugh in the world”
ability to learn from tion of pain, heat, and cold to the and state “she’s going to conquer the
her mistakes of brain. Anhidrosis, or the inability to world” (Tresniowski et al., 2005).
injuring herself? sweat, can cause life-threatening (Adapted from Morton, 2004;
problems such as developing dan- Tresniowski et al., 2005)
gerously high fevers because people
aren’t able to lower their body tem-
perature by sweating.

Living life without feeling pain is
not as wonderful as one might think.
Pain serves an important function
by telling our brain that something
is wrong and something needs to be
done to correct it. Imagine having
appendicitis and not feeling pain.
Appendicitis is especially dangerous
for people with CIPA because they
wouldn’t know a problem existed
until after their appendix burst.
Also, while most people shift their

118 M O D U L E 5 S E N S A T I O N

Links to Learning

Key Terms/Key People Learning Activities

acupuncture, 113 nearsightedness, 95 PowerStudy for Introduction PowerStudy 4.5™
adaptation, 93 neural deafness, 115 to Psychology 4.5
a erimage, 99 olfaction, 107
amplitude, 100 olfactory cells, 107 Use PowerStudy to complete quizzes and learning activities for Sensation. e
auditory association opponent-process DVD also includes interactive versions of the Summary Test on pages 116–117
and the critical thinking questions for the article on page 118, key terms, an out-
area, 103 theory, 99 line and an abstract of the module, and an extended list of correlated websites.
auditory canal, 102 optic nerve, 97
auditory nerve, 103 ossicles, 102 CengageNOW!
basilar membrane, 103 outer ear, 102 www.cengage.com/login
cochlea, 102 pain, 112 Want to maximize your online study time? Take this easy-
cochlear implant, 115 perceptions, 93 to-use study system’s diagnostic pre-test and it will create a personalized study
color blindness, 99 pitch, 100 plan for you. e plan will help you identify the topics you need to understand
conduction deafness, 115 place theory, 104 better and direct you to relevant companion online resources that are specific
cones, 96 placebo, 111 to this book, speeding up your review of the module.
cornea, 95 placebo effect, 111
decibel, 101 primary auditory Introduction to Psychology Book Companion Website
dichromats, 99 www.cengage.com/psychology/plotnik
direction of sound, 104 cortex, 103 Visit this book’s companion website for more resources to help you
disgust, 110 primary visual cortex, 97 study, including learning objectives, additional quizzes, flash cards, updated
double-blind study, 111 pupil, 95 links to useful websites, and a pronunciation glossary.
dread, 113 retina, 95, 96
endorphins, 113 rods, 96 Study Guide and WebTutor
external ear, 102 sensations, 93 Work through the corresponding module in your Study
farsightedness, 95 somatosensory cortex, 108 Guide for tips on how to study effectively and for help learning the material
flavor, 106 sound waves, 100 covered in the book. WebTutor (an online Study Tool accessed through your
frequency theory, 104 taste, 106 eResources account) provides an interactive version of the Study Guide.
gate control theory, 112 taste buds, 106
hair cells, 103 touch, 108
inner ear, 102 transduction, 93
iris, 95 trichromatic theory, 98
lens, 95 tympanic membrane, 102
loudness, 100, 104 vertigo, 105
Meniere’s disease, 105 vestibular system, 105
middle ear, 102 visible spectrum, 94
monochromats, 99 visual agnosia, 97
motion sickness, 105 visual association areas, 97

Suggested Answers to Critical Thinking 4. Most children learn to avoid engaging in behaviors that result
in pain. For example, children quickly learn not to touch a hot
1. A case study is an in-depth analysis of the thoughts, feelings, beliefs, flame after burning their hands by doing so. Learning not to
or behaviors of one person. There are very few people who cannot feel engage in repetitive self-injurious behavior is challenging for
pain, and so a thorough study of one person would be helpful. Ashlyn because she cannot feel pain.

2. Afferent neurons carry information in the form of electrical signals to 5. Acupuncture is a procedure used to reduce various kinds of pain.
the spinal cord and brain. Signals for sensing pain, heat, and cold are People with CIPA do not feel pain, and therefore acupuncture
not being carried to the brain in people with CIPA. would not be an effective treatment.

3. The state in which our physiological arousal is kept in balance, an opti- 6. The same nerve ending responds to pain and temperature, but
mum level, is called homeostasis. By not being able to sweat, Ashlyn’s other nerve endings (such as hair receptors) respond to differ-
body has difficulty maintaining body temperature at an optimum level. ent types of touch stimulation, such as pressure, making it is
The hypothalamus, a part of the limbic system, controls the autonomic possible for Ashlyn to feel her parents tickling and hugging her.
nervous system (sympathetic and parasympathetic systems), and they
work together to keep the body’s level of arousal in balance. L I N K S T O L E A R N I N G 119

6 Perception
MODULE

Photo Credit: © AP Images/Miguel Villagran
A. Perceptual Thresholds 122 I. ESP: Extrasensory Perception 138
B. Sensation Versus Perception 124 J. Application: Creating Perceptions 140
C. Rules of Organization 126 Summary Test 142
D. Perceptual Constancy 128 Critical Thinking 144
E. Depth Perception 129
F. Illusions 132 Taste Shapes? Hear Colors? Smell Sounds? 145
Concept Review 134 Links to Learning
G. Research Focus: Influencing Perception 135
H. Cultural Diversity: Influence on Perceptions 136 PowerStudy 4.5™
Complete Module

120

Introduction

Silent Messages White Spot On Friday, Maria had to take time from work
Although it seemed like an ordinary week, for her annual physical exam, which included
How can Maria and her 7-year-old daughter, Gabrielle, Can the

I be more would be involved in three relatively normal doctor be a mammogram. In the past, the doctor had
events that could change their lives forever. simply said that the results of her mammo-
confident? On Tuesday, Maria’s new boss unfairly sure? gram were negative. This time, the doctor

criticized her work and made her feel insecure and unsure of her- brought in her mammogram, which looked like an X ray. He
self. During her lunch hour, she browsed through a bookstore to pointed to a small white spot and said in a
find something on building confidence. She was intrigued by an concerned voice, “I’m afraid that this tiny
audio CD titled “Improve Self-Esteem.” The white dot may be a cancerous tumor.” The
instructions read, “ e listener hears only doctor’s words took her breath away. Finally,
relaxing music, but the unconscious hears Maria asked in a terrified whisper, “Are you
and automatically processes subliminal absolutely sure that spot is cancer?” e doc-
messages that boost self-esteem. In a few tor paused for a minute, looked again at the
short weeks, the listener is guaranteed to mammogram, and said, “I can’t be absolutely
have more confidence and self-esteem. If sure the spot is cancerous until we do a biop-
you’re not completely satisfied, return the sy. All I can say is that there is a good possi-
CD for a full refund.” Maria had heard bility that it is.” As Maria scheduled her Why should two
Can subliminal about CDs with subliminal persuasion biopsy, she would never forget seeing that doctors read each
messages change a from a friend who claimed that she used white spot on the mammogram.
person’s behaviors? mammogram?

a weight-reduction CD that helped her Perceiving Things
lose 20 pounds. When Maria asked about the effectiveness of sub-
liminal recordings, the salesperson said that he had a friend who
increased his motivation to study by listening to one of these CDs. At first glance, these three events—buying a
Maria smiled and said, “Well, it’s guaranteed, so what have I got to What are subliminal CD, being bitten by a dog, and

lose?” She bought the CD, put it in her purse, and as she walked out the three seeing a spot on a mammogram—seem to

the door, she was already feeling a little more confident. questions? have nothing in common. In fact, these
events raise three basic questions about how
we perceive things.
Nice Dog, Mean Dog Maria’s subliminal CD raises the first question: Are there things
that we perceive but are not aware of, and can these things influ-
On Saturday a ernoon, Maria took her daugh- ence our behaviors?
What’s a ter, Gabrielle, to play at the local park, which Maria’s mammogram raises the second question: How large or

Photo Credits: top right, © Howard Sochurek/Corbis; bottom left, © image100/SuperStock mean dog? had slides, swings, ropes, and even a small unusual must things be before our senses can detect them? is
trampoline. As Gabrielle was walking toward
the trampoline, she saw a beautiful white and brown dog sitting by is a very important question, since the answer may have serious
health consequences (Grady, 2008).
its owner. Gabrielle loved animals, and she ran toward the dog. e Finally, Gabrielle’s painful experience with a dog raises the
dog’s owner was deep in conversation and did not notice the cute
little girl running toward the beautiful dog. As Gabrielle came closer, third question: How much are the things we perceive influenced
or biased by our cultural, learning, emotional, and personal expe-
she thrust out her hands to pet the dog’s smooth black nose. The riences (Goldstein, 2010)? These three questions are the key to
movement of Gabrielle’s hands startled the dog, who reflexively
snarled and then snapped at the hands coming at its nose. Gabrielle understanding how we perceive our world.

felt the pain as the dog’s teeth nipped two of her fingers, which What’s Coming
immediately started to bleed. e owner turned to see what had hap-
pened and quickly pulled the dog away as Maria came running. We’ll discuss what perceptual thresholds are, how sensations differ
Maria took Gabrielle in her arms, soothed from perceptions, how sensations are combined to form percep-
her, and then examined the small cuts tions, how objects can undergo great changes yet appear the same
on her fingers. Gabrielle looked at her to us, how our senses are fooled by illusions, how cultural experi-
bleeding fingers and then at the big, ugly, ences change perceptions, whether there is good evidence for ESP
white and brown dog that had bit her and (extrasensory perception), and whether the newest kind of perceiv-
said in a tearful voice, “I hate that dog. ing, called virtual reality, can fool our senses into believing we’re
Bad dog.” Seeing her daughter’s reaction, in a three-dimensional world.
Maria began to have doubts about her
plans to surprise Gabrielle with a cute How does a bad experience Let’s start with the first and most basic perceptual question:
little puppy for her birthday. create a bad perception? At what point do you become aware of seeing, hearing, smelling,
tasting, or feeling some stimulus, object, or event?

I N T R O D U C T I O N 121

A. Perceptual Thresholds

Becoming Aware of a Stimulus

When do you Imagine suddenly becoming deaf or For example, Maria is not aware of, or does not hear, subliminal
blind, unable to hear what people are messages recorded on the CD because these messages are below
know something saying or to see where you are going. her absolute threshold for hearing. To understand how the absolute
is happening? Only then would you realize that threshold is determined, imagine that Maria is presented
your senses provide a continu- with a series of auditory messages that slowly increase
ous stream of information about your world. Your senses in intensity. Maria is asked to press a button when
tell you that something is out there, and your percep- she first hears a message. You may think that there
tions tell you what that something is. However, there are will be a certain level or absolute value of intensity
some sounds and objects you may not be aware of (loudness) at which Maria will first report hearing a
because the level of stimulation is too low and does not tone. e idea that there is an absolute threshold was
exceed the threshold of a particular sense. proposed by Gustav Fechner (1860), an important
Threshold refers to a point above which a stimulus is Subliminal means that a person historical figure in perceptual research. However,
perceived and below which it is not perceived. The threshold has less than a 50% chance of as you’ll see, Fechner had difficulty identifying the
absolute threshold as he defined it.
determines when we first become aware of a stimulus. detecting the message.

1 At first, Gustav Fechner (FECK-ner) defined the absolute threshold as 4 e concept of an absolute
threshold has very real conse-
the smallest amount of stimulus energy (such as sound or light) that can be quences in detecting breast
observed or experienced. cancer.
Each year, about 200,000
According to Fechner’s definition, if Maria’s hearing could always be women are diagnosed with
measured under exactly the same conditions, her absolute threshold would breast cancer and 40,000
always remain the same. Although Fechner tried various methods to identify women die of the disease,
absolute thresholds, he found that an individual’s threshold was not absolute making it the most frequently Possible cancerous
and, in fact, differed depending on the subject’s alertness and the test situa- occurring cancer in American breast tumor stands
tion. Because of this variability in measurement, researchers had to redefine women and, after lung can- out as a white spot.
absolute threshold.
cer, the second-leading cancer killer (Grady, 2008).
2 e graph below shows how the absolute threshold was redefined. Doctors read 35 million mammograms (X rays of
Absolute threshold is the intensity level of a stimulus such that a person will have breasts) each year to look for white spots that stand
a 50% chance of detecting it. out on a black background; these white spots indicate
tumors (photo above) (Grady, 2008). However, some
According to this updated definition, Maria’s absolute threshold is the women have so much connective breast tissue, which
point on the graph where she has a 50% chance of hearing the message. also appears white, that tiny white tumors go unde-

Once we have determined Maria’s absolute threshold for hearing messages,
we can define a subliminal stimulus.

Absolute threshold: 50% tected. ese women are at an increased risk of having
chance of hearing message 100% cancer, yet it is 17 times more likely to not be detected
Subliminal chance of using mammograms (Boyd, 2007). This problem,
stimulus: hearing combined with doctors’ lack of expertise, results in
0–49% message missing up to 30% of tumors (Pisano et al., 2005).
chance of Increasing intensity Accuracy problems. Researchers are constantly
hearing looking for ways to lower the threshold for detecting
message cancerous tumors and thus save patients’ lives. The
accuracy of identifying cancerous tumors increases
when mammograms are read independently by two
3 e graph above shows that a subliminal stimulus can occur at any point doctors or when one doctor and a new computer pro- Photo Credit: © Howard Sochurek/Corbis
gram designed to detect tumors read them (BBC,
below the absolute threshold (50% chance of hearing). 2008a; M.Healy, 2000). Recently, digital mammograms,
A subliminal stimulus has an intensity that gives a person less than a 50% chance which allow for images to be enhanced or magnified
on a computer screen, have been found to be better at
of detecting the stimulus. detecting cancerous tumors in women who have a lot
Because subliminal messages can occur in a wide range (0–49%), Maria of connective tissue (Grady, 2008; Kincaid, 2007).
The problem of determining thresholds also
may or may not report hearing them on the CD. For example, Maria would applies to the question of how we know a stimulus
never report hearing messages of very low intensity (0% level) but may has changed in intensity. We’ll discuss this next.
sometimes report hearing messages of higher intensity (49%).

We’ll discuss whether subliminal messages can change behaviors or
attitudes, such as increasing self-esteem, in the Research Focus (p. 135).

122 M O D U L E 6 P E R C E P T I O N

Weber’s Law

Why is that Suppose people are playing music too loud Weber’s Law Explained
music still and you ask them to turn down the vol- Weber’s law explains that, at lower intensities, small changes
ume. Even a er they turn it down, it may between two stimuli can be detected as just noticeable differ-
too loud? still seem just as loud as before. e expla- ences (JNDs); however, at higher intensities, only larger
changes between two stimuli can be detected as JNDs.
nation for this phenomenon can be found
in the work of another historical figure in perception, E. H.
Weber (VEY-ber).
Weber worked on the problem of
how we judge whether a stimulus, Stimulus: Lower Higher

such as loud music, has increased or 1 JND. e same height of each step illustrates
decreased in intensity. This problem
involves measuring the difference in your ability to detect “one sensory unit” of
thresholds between two stimuli, such as a just noticeable difference between
very loud music and not-quite-so-loud the loudness of two sounds.
music. To solve this problem, Weber
Smallest detectable (1834) developed the concept of a just
increase or decrease noticeable difference.
A just noticeable difference, or JND,
in sound is a JND.

refers to the smallest increase or decrease in the intensity of a stimulus

Photo Credits: left, © Arman Zhenikeyev/Alamy; bottom, © Pat Bruno/Positive Images that a person is able to detect. 2 Lower intensities. e 3 Higher intensities. e
For example, to measure a just noticeable difference in
small width of this step indi- considerable width of this
weight, Weber asked people to compare stimuli of varying inten- cates that, at lower intensities, step indicates that, at higher
sities and indicate when they could detect a difference between you need only a small differ- sound intensities, you need
them. He discovered that if he presented two stimuli with very ence in order to detect a just a larger difference to detect
low intensities, such as a 2-ounce weight versus a 3-ounce noticeable difference between a just noticeable difference
weight, people could easily detect the difference between them. the loudness of two sounds. between the loudness of two
However, if he presented stimuli with high intensities, such as sounds. is statement fol-
a 40-pound weight versus a 41-pound weight, people could no is statement follows from lows from Weber’s law, which
longer detect the difference. For higher-intensity stimuli, such as Weber’s law, which says that says that a larger difference
heavy weights, a much larger difference in intensity was required only a small difference in in intensity is required for
for the difference to be noticed (Kantowitz et al., 2009). intensity is required for you to you to detect a just noticeable
detect a just noticeable differ- difference when judging
Weber’s observations on what it takes to detect just notice- ence when judging stimuli of stimuli of higher intensity.
able differences were the basis for what became known as lower intensity.
Weber’s law. Besides explaining the
problem with loud stereos,
Weber’s law states that the increase in intensity of a stimulus need- Weber’s law has many practi-
ed to produce a just noticeable difference grows in proportion to the cal applications, such as how
to detect a difference in the
intensity of the initial stimulus. so ness of towels.
We’ll use Weber’s law (please read right figure) to explain

how if someone is playing the stereo very loud, it must be turned
down a great deal, usually more than the person prefers to turn
it down, for you to detect a just noticeable decrease in volume.

Just Noticeable Difference (JND) and Soft Towels

Every year, industry and business spend bil- gave an average so ness rating of 5 to towels washed repeatedly
Which towel lions of dollars to make sure that consumers without so ener and an average rating of 18 to towels washed with
is softer? can detect just noticeable differences between so ener. Researchers concluded that fabric so eners worked, since

this year’s and last year’s subjects could easily detect a just noticeable difference in
cars, shampoos, cereals, and fashions. For exam- so ness (S. I. Ali & Begum, 1994). is is but one practical
ple, consumers spend millions of dollars each application of Weber’s law and just noticeable difference
year on fabric so eners, which are added during (JND) in industry.
washing and are claimed to make clothes feel So far, we’ve focused on how you become aware of and
softer. To test such claims, researchers asked detect stimuli and distinguish between their intensities.
subjects to feel towels washed with and without a Next, we’ll discuss one of the most interesting questions
fabric so ener and rate the so ness of the towels Judging the softness of in perception: How do you change meaningless bits of
on a scale from 1 (hard) to 30 (very so ). Subjects towels involves noting JND. sensations into meaningful and complete perceptions?

A . P E R C E P T U A L T H R E S H O L D S 123

B. Sensation Versus Perception

Basic Differences

How can I Much of your success in being happy and the process of changing sensations into perceptions is influenced by
successful depends on your ability to whether you are alert, sleepy, worried, emotional, motivated, or affect-
be successful respond intelligently and adapt appro- ed by the use of a legal or illegal drug. For example, drinking alcohol
and happy? priately to changes in your environment causes perceptions in social situations to be less rational and more
(NAMHC, 1996). The first step in uninhibited, causing people under its influence to act aggressively,
responding and adapting involves gathering millions of mean- make terrible decisions, create problems, or say really dumb things
ingless sensations and changing them into useful perceptions. (R. Goldberg, 2006; Maisto et al., 2008). As you are about to discover,
Because your brain changes sensations into perceptions so sensing and perceiving are as different as night and day.
quickly, automatically, and with very little awareness, you might
assume that what you see (sense) is what you perceive. However, For example, quickly glance at the black-and-white figure below
on the le and then look away and describe what you saw.

Sensations Perceptions

Initially, the le figure appears to be As you look at the right stimulus, your
a bunch of meaningless lines, spaces, brain is processing many thousands of
and blobs, which, for the sake of sim- visual sensations involving lines, curves,
plicity, we’ll take the liberty of call- textures, shadows, and colors. Then,
ing visual sensations. In real life, we instantaneously, automatically, and with-
rarely if ever experience sensations out awareness, your brain combines these
because, as we’ll explain on the next thousands of sensations into a percep-
page, they are immediately turned tion—an orange tiger’s face against a
into perceptions. green background.
A sensation is our first awareness of A perception is the experience we have

some outside stimulus. An outside stimu- Sensations are Perceptions are after our brain assembles and combines thou-
lus activates sensory receptors, which in MEANINGLESS bits MEANINGFUL patterns, sands of individual, meaningless sensations
turn produce electrical signals that are into a meaningful pattern or image. However,
transformed by the brain into meaningless of information. images, or sounds. our perceptions are rarely exact replicas of the

bits of information. original stimuli. Rather, our perceptions are usually changed, biased, col-

You can approximate how visual sensations may look by ored, or distorted by our unique set of experiences. Thus, perceptions are
placing half of a ping-pong ball over your eye. As you look our personal interpretations of the real world.
through this nearly opaque ping-pong ball, you’ll see shadows, If you now look at the black-and-white drawing on the upper le ,
textures, and dark shapes but nothing meaningful; these are your brain will automatically combine the formerly meaningless
similar to sensations. shapes and blobs into a tiger’s face. is is an approximate example
Another example that illustrates the difference between sen- of how meaningless sensations are automatically combined to form
sations and perceptions is the photo below. Your first impression meaningful perceptions.
consists of meaningless shapes, textures, and blotches of color, One important feature of perceptions is that they are rarely exact
which we’ll again take the liberty of calling visual sensations. copies of the real world. For example, people who listen to the same
However, you can turn these meaningless sensations into a song or music can react very differently (happy, relaxed, agitated,
meaningful image—a perception—by using the following clues. bored). To study how personal preferences for music can bias our
is photo is an ultrasound image of a fetus in the womb. e perceptions, researchers assigned students who preferred listen-
fetus is lying on his back with his rounded tummy on the le ing to classical music over other types of music to groups that were
and his large head on the right. Above his head instructed to sit and relax while listening to either Photo Credit: bottom, Custom Medical Stock Photo
is the right arm and hand, and you can even 20 minutes of classical music or 20 minutes of rock
count the five tiny fingers. You can also see music. Researchers used physiological measures
that the fetus is sucking on his thumb. Once to record anxiety levels both before and a er sub-
you know what to look for, you automatically jects listened to music. Findings showed that only
change the random blotches of colors and those subjects who listened to their favorite kind of
shapes into the perception of a fetus. music (classical music) had a decrease in anxiety
Obviously, it would be impossible to levels (Salamon et al., 2003).
respond, adapt, and survive if you had to rely To show that no two individuals perceive the
only on sensations. You can now appreciate world in exactly the same way, we’ll explain how
the importance of changing sensations into You can turn this sensation into a your personal experiences change, bias, and even
perceptions. perception by reading the text (left). distort your perceptions.

124 M O D U L E 6 P E R C E P T I O N

Changing Sensations into Perceptions

How does a It is most unlikely that you have ever For example, at the beginning of this module we told
experienced a “pure” sensation you how 7-year-old Gabrielle’s perception of a dog was
“nice” doggie because your brain automatically changed from “nice” to “bad” by her personal experi-
become a and instantaneously changes sensa- ence of being bitten. The next time Gabrielle sees a
dog, she won’t see just a four-legged creature with ears,
“bad” doggie? tions into perceptions. Despite what nose, and tail; she will see a “bad” four-legged crea-
you may think, perceptions do not ture. To understand how sensations become percep-
exactly mirror events, people, situations, and objects in your tions, we have divided the perceptual process into a
environment. Rather, perceptions are interpretations, which series of discrete steps that, in real life, are much
means that your perceptions are changed or biased by your There are five more complex and interactive.
personal experiences, memories, emotions, and motivations. steps in forming

perceptions.

1 Stimulus. Since normally we experience only 4 Brain: association areas. Each sense sends
perceptions, we are not aware of many preceding
steps. e first step begins with some stimulus, its particular impulses to a different primary area
which is any change of energy of the brain where impulses are changed into sen-
in the environment, such as sations, which are meaningless bits of informa-
light waves, sound waves, tion, such as shapes, colors, and textures (top Sensations are
mechanical pressure, or right). e “sensation” impulses are then sent to meaningless bits
chemicals. e stimulus the appropriate association areas in the brain. e of information.
activates sense receptors in association areas change meaningless bits into Association areas
the eyes, ears, skin, nose, or meaningful images, called perceptions, such as a change sensations into
mouth. In Gabrielle’s case, dog (bottom right). perceptions—dog.
A stimulus (dog)
activates receptors In Gabrielle’s case, impulses from her eyes
the stimuli are light waves in the senses. would be changed into visual sensations by the
reflecting off the body of a dog. primary visual area and into perceptions by the
visual association areas. However, Gabrielle’s per-
2 Transduction. A er entering Gabrielle’s eyes, ception of a dog would be changed, biased, and
light waves are focused on the retina, which contains even distorted by many psychological, emotional,
photoreceptors that are sensitive to light. e light and cultural factors.

waves are absorbed by 5 Personalized perceptions. Each of us has a unique set of personal experi-
photoreceptors,
which change
physical energy ences, emotions, and memories that are automatically added to our perceptions
by other areas of the brain. As a result, our perceptions are not a mirror but a
into electrical changed, biased, or even distorted copy of the real world (Goldstein, 2010). For
signals, called transduction.
e electrical signals are example, the visual areas of Gabrielle’s brain automatically assemble many
changed into impulses that thousands of sensations into a meaningful pattern,
travel to the brain. Sense organs Senses change which in this case is a dog. Now, however, Gabrielle
stimulus into doesn’t see just an ordinary white and brown dog
do not produce sensations but electrical signals.

simply transform energy into electrical signals. because other brain areas add her emotional expe-
rience of being bitten. Thus, Gabrielle perceives
this white and brown, four-legged creature to be a
3 Brain: primary areas. Impulses from sense “bad dog.” For this same reason, two people can
organs first go to different primary areas of the brain. look at the same dog and have very different per-
For example, impulses from the ear go to the tempo- ceptions, such as cute dog, great dog, bad dog,
ral lobe, from touch to the smelly dog, or friendly dog. us, your perceptions
parietal lobe, and from the are personalized interpretations rather than true
eye to areas in the occipi- copies of objects, animals, people, and situations in
tal lobe. When impulses the real world.
reach primary areas in The process of assembling and organizing
the occipital lobe, they sensations into perceptions was of great inter-
are first changed into Occipital lobe est to early psychologists, who disagreed on
how perceptions were formed. As you’ll see Perceptions do not mirror
sensations. However, Primary areas of brain reality but rather include our
change electrical signals biases, emotions, and
Gabrielle would not into sensations. next, their debate resulted in a very interesting memories to reflect reality.
report seeing sensations. perceptual controversy.

B . S E N S A T I O N V E R S U S P E R C E P T I O N 125

C. Rules of Organization

Structuralists Versus Gestalt Psychologists

What was In the early 1900s, two groups of psychologists engaged in a heated debate over how perceptions are formed. One
the great group, called the structuralists, strongly believed that we added together thousands of sensations to form a percep-
debate? tion. Another group, called the Gestalt psychologists, just as strongly believed that sensations were not added but
rather combined according to a set of innate rules to form a perception (M. A. Peterson et al., 2007). One group
won the debate, and you might guess which one before you read further.

Structuralists Gestalt Psychologists

As you look at the scene in the middle The Gestalt psychologists said that
of this page, you perceive a fountain at perceptions were much too complex to
the bottom with shrubs and palm trees be formed by simply adding sensations
on the sides, all topped by a large dome together; instead, they believed that
of glass windows. Is it possible that perceptions were formed according to
your brain combined many thousands a set of rules.
of individual sensations to produce Gestalt psychologists believed that our

this complex perception? If you answer brains follow a set of rules that specify how

yes, you agree with the structuralists. individual elements are to be organized into

The structuralists believed that you a meaningful pattern, or perception.

add together hundreds of basic elements to Unlike structuralists, Gestalt psy-

form complex perceptions. They also chologists said that perceptions do not

believed that you can work backward to result from adding sensations. Rather,

break down perceptions into smaller and perceptions result from our brain’s

smaller units, or elements. ability to organize sensations accord-

Structuralists spent hundreds of ing to a set of rules, much as our brain
hours analyzing how perceptions, such follows a set of rules for organizing
as a falling ball, might be broken down words into meaningful sentences
into basic units or elements. They (Donderi, 2006; Quinn et al., 2008).
believed that once they understood the So how would Gestalt psychologists
process of breaking down perceptions, explain your perception of the scene
they would know how basic units are on the le ? ey would say that your
recombined to form perceptions. us, perception was not formed by simply
structuralists believed that you add adding bits of tile, steel, and foliage
together basic units to form percep- into a whole image. Rather, your brain
tions, much as you would add a col- Do you add together basic elements to form perceptions or does automatically used a set of rules to
umn of numbers to get a total. your brain have rules for forming perceptions? combine these elements to form a uni-

For example, structuralists would say that you add together fied whole. To emphasize their point, Gestalt psychologists came
hundreds of basic units, such as colors, bricks, leaves, branches, up with a catchy phrase, “ e whole is more than the sum of its
tiles, pieces of glass, and bits of steel, to form the perception of the parts,” to mean that perceptions are not merely combined sensa-
scene above. However, the structuralists’ explanation of adding bits tions. e Gestalt psychologists went one step further; they came
to form a perception was hotly denied by Gestalt psychologists. up with a list of organizational rules. Photo Credit: Painting by Richard Haas, photo © Bill Horsman

Evidence for Rules Equally convincing evidence that the whole is greater than the
Gestalt psychologists won their debate with sum of its parts came from a remarkably detailed series of studies
Who won the structuralists for two reasons. The first in which Gestalt psychologists presented stimuli to subjects and
then asked them to describe what they perceived (Rock & Palmer,
the debate? reason comes from our own personal percep- 1990). On the basis of subjects’ reports, researchers discovered
tual experiences. For example, as you look that forming perceptions involved more than simply adding and
again at the beautiful scene above, we must reveal that it is entirely combining individual elements. Modern research has generally
fake. e scene, which looks so realistic and three-dimensional, is supported the early Gestalt conclusion that our brains actually
actually painted on a flat wall. It seems impossible that we could do follow a set of rules for organizing and forming perceptions
have such a complex, three-dimensional perceptual experience (Quinn et al., 2008). We’ll explain these rules for organizing
from simply combining bits and pieces of bricks, branches, leaves, perceptions next.
and steel. This fake but truly realistic scene makes the Gestalt
motto come to life: “ e whole is more than the sum of its parts.”

126 M O D U L E 6 P E R C E P T I O N

Organizational Rules

How many It is very hard to believe that the scene on As you look at the scene, your brain
the preceding page (repeated here on the automatically organizes many hun-
rules are there? right) was actually painted on a flat wall. dreds of visual stimuli, including colors,
One reason you perceive this scene as com- textures, shadows, bricks, steel, glass,
plex and 3-dimensional is that the painter followed many of the leaves, and branches, according to one
Gestalt rules of organization (Han & Humphreys, 1999). or more of the six perceptual rules of
Rules of organization, which were identified by Gestalt psychologists, organization described below. We’ll use
a relatively simple figure to illustrate
specify how our brains combine and organize individual pieces or elements each rule.

into a meaningful perception.

Figure-Ground Similarity

One of the most basic rules in organizing perceptions is picking out the As you look
object from its background. As you look at the figure on the le , you will at this figure
automatically see a white object standing out against a red background, filled with
which illustrates the figure-ground principle. light and dark
blue dots, you
The figure-ground rule states that, in organizing stimuli, we tend to automati- see a dark blue
cally distinguish between a figure and a ground: The figure, with more detail, stands
numeral 2.
out against the background, which has less detail. The similarity rule states that, in
ere is some evidence that our ability to separate figure from ground is organizing stimuli, we group together

an innate response. For example, individuals who were blind from an early age and had their elements that appear similar.
sight restored as adults were able to distinguish between figure and ground with little or no The similarity rule causes us to
training (Senden, 1960). e figure-ground rule is one of the first rules that our brain uses to
organize stimuli into a perception (Vecera, 2002). is particular image is interesting because, group the dark blue dots together
as you continue to stare at it, the figure and ground will suddenly reverse and you’ll see profiles and prevents us from seeing the
of two faces. However, in the real world, the images and objects we usually perceive are not figure as a random arrangement of
reversible because they have more distinct shapes (Humphreys & Muller, 2000). light and dark blue dots.

Closure Proximity

Although the lines are incomplete, you can eas- Notice that although there are exactly eight circles in
ily perceive this drawing as a cat or dog. each horizontal line, you perceive each line as formed
by a different number of groups of circles.
The closure rule states that, in organizing stim-
uli, we tend to fill in any missing parts of a figure The proximity rule states that, in organizing stimuli, we
group together objects that are physically close to one another.
and see the figure as complete.
For example, the closure rule explains You automatically group circles that are close
together and thus perceive the first line as composed
why you can fill in letters missing on a sign of three groups (Kubovy & Wagemans, 1995).
or pieces missing in a jigsaw puzzle.

Simplicity Continuity

Photo Credit: top, Painting by Richard Haas, photo © Bill Horsman Look at figure A and then As you scan this figure, keep track of the path that your eyes
decide if it is made up of the follow. Most people’s eyes will move from le to right in a con-
pieces shown in figure B, C, or tinuous line, following the path from A to B or from C to D.
D. Almost everyone sees fig-
ure A as made up of the pieces The continuity rule states that, in organizing stimuli, we tend to
in figure B—an oval with an favor smooth or continuous paths when interpreting a series of
overlapping square. points or lines.

The simplicity rule states that For example, the rule of continuity predicts that you do
stimuli are organized in the sim- not see a line that begins at A and then turns abruptly to C or to D.

plest way possible. Conclusion. These figures demonstrate the Gestalt rules of organizing stimuli
For example, almost no one into perceptions. Young children slowly learn these perceptual rules and begin to use
them as early as infancy (Quinn et al., 2008). As adults we use these rules to orga-
sees figure A as having been nize thousands of stimuli into perceptions, especially stimuli in print and advertise-
formed from the complicated ments. For doctors who read mammograms and other X rays, Gestalt rules such as
pieces shown in figure C or figure-ground, similarity, and proximity are essential in their daily work (Koontz &
figure D. is rule says that we Gunderman, 2008).
tend to perceive complex figures as divided into
several simpler figures (Shimaya, 1997). Next, we examine the question: How can objects change yet appear to remain
the same?

C . R U L E S O F O R G A N I Z A T I O N 127

D. Perceptual Constancy

Size, Shape, Brightness, & Color Constancy

Why don’t The study of perception is happens to its shape on your retina.
full of interesting puzzles, These are examples of how percep-
speeding cars such as how cars, people, tions remain constant, a phenome-
shrink? and pets can change their non called perceptual constancy.
Perceptual constancy refers to our ten-
shapes as they move about yet
we perceive them as remaining the same size and shape. For exam- dency to perceive sizes, shapes, brightness, and colors as remaining the
ple, a car doesn’t grow smaller as it speeds away, even though its
shape on your retina grows smaller and smaller. A door doesn’t same even though their physical characteristics are constantly changing.
become a trapezoid as you walk through it, even though that’s what We’ll discuss four kinds of perceptual constancy—size, shape,

brightness, and color.

Size Constancy Shape Constancy Brightness and Color Constancy Photo Credit: © Pat Bruno/Positive Images
Each time you move a book, its
Imagine a world in which you image on your retina changes If you look into your dimly lit closet,
perceived that every car, person, from a rectangle to a trapezoid. all the brightly colored clothes will
or animal became smaller as it But you see the book’s shape as appear dull and grayish. However,
moved away. Fortunately, we remaining the same because of because of brightness and color con-
are spared from coping with so shape constancy. stancy, you still perceive brightness
much stimulus change by percep- and colors and have no trouble select-
tual constancy, one type of which Shape constancy refers to your ing a red shirt.
is size constancy. tendency to perceive an object as
Size constancy refers to our ten- retaining its same shape even though Brightness constancy refers to the
dency to perceive objects as remain- when you view it from different tendency to perceive brightness as remain-
angles, its shape is continually ing the same in changing illumination.
ing the same size even when their changing its image on the retina.
images on the retina are continu- Color constancy refers to the tendency
ally growing or shrinking. e figure below shows to perceive colors as remaining stable
that when you look down at a despite differences in lighting.
As a car drives away, it rectangular book, it projects a
projects a smaller and smaller rectangular shape on your retina. For example, if
image on your retina (le you looked at this
figure). Although the retinal However, if you move the book young girl’s sweater
image grows smaller, you do not perceive the car farther away, it projects trapezoi- in bright sunlight,
as shrinking because of size constancy. A similar dal shapes on your retina (figure it would be a bright
process happens as a car drives toward you. below), but you still perceive the yellow.
As the same car drives closer, notice in the book as rectangular because of
figure below how it projects a larger image on your shape constancy. If you looked at her
retina. However, because of size constancy, you do same yellow sweater
not perceive the car as becoming larger. Besides size and shape con- in dim light, you
Size constancy is some- stancy, there is also brightness would still perceive
thing you have learned and color constancy. the color as a shade
from experience with of yellow, although
moving objects. You have it is duller. Because
learned that objects do not of color constancy,
increase or decrease in size colors seem about the same even when
as they move about. For lighting conditions change.
example, an individual who
was blind since birth and However, if the light is very dim,
had his vision restored as objects will appear mostly gray
an adult looked out a fourth- because you lose color vision in very
story window and reported dim light.
seeing tiny creatures moving on
the sidewalk. Because he had not Perceptual constancy is important
learned size constancy, he did not know the tiny because it transforms a potentially ever-
creatures were full-size people (Gregory, 1974). changing, chaotic world into one with
We also perceive shapes as remaining the same. stability and comforting sameness.

Our next perceptual puzzle is how
our eyes can see only two-dimensional
images but our brain can transform
them into a three-dimensional world.

128 M O D U L E 6 P E R C E P T I O N

E. Depth Perception

Binocular (Two Eyes) Depth Cues Depth perception refers to the ability of your eye and brain to add a

How can you Normally, movies are shown in only two
dimensions: height and width. But if you third dimension, depth, to all visual perceptions, even though images
see in three have ever seen a movie in 3-D (using special projected on the retina are in only two dimensions, height and width.
dimensions? glasses to see three dimensions: height, e object on the le has been given a three-dimensional look
width, and depth), you know the by making it seem to have depth. It is impossible
thrill of watching objects or animals leap off the screen for most sighted people to imagine a world with-
so realistically that you duck or turn your head. You out depth, since they rely on depth perception
may not have realized that your eyes automatically to move and locate objects in space. e cues for
give you a free, no-glasses, 3-D view of the world. depth perception are divided into two major classes:
And the amazing part of seeing in 3-D is that every- binocular and monocular.
thing projected on the retina is in only two dimen- Binocular depth cues depend on the movement of both

sions, height and width, which means that your brain eyes (bi means “two”; ocular means “eye”).

combines a number of different cues to add a third Seeing in 3-D means seeing We’ll start with two binocular cues: convergence
dimension—depth (J. M. Harris & Dean, 2003). length, width, and DEPTH. and retinal disparity.

Convergence

When you have an eye exam, the doctor usually asks you to the bubble. You can experience convergence by hold-
follow the end of her finger as she holds it a few feet away ing a finger in front of your nose and slowly bring-
and then slowly moves it closer until it touches your ing it closer to your nose. Your finger appears to
nose. is is a test for convergence. move closer to your nose because the muscles that
Convergence refers to a binocular cue for depth percep- are turning the eyes inward produce signals cor-

tion based on signals sent from muscles that turn the eyes. To responding to convergence. e more your eyes

focus on near or approaching objects, these muscles turn turn inward or converge, the nearer the object

the eyes inward, toward the nose. The brain uses the sig- appears in space. e woman in the photo sees

nals sent by these muscles to determine the distance of the bubble because of convergent clues from her

the object. turned-in eyes.

The woman in the photo at the right is demon- During convergence the eyes turn e second binocular cue comes from having
strating the ultimate in convergence as she looks at inward to see objects up close. an eye on each side of your face.

Retinal Disparity

One reason it’s an advantage to have an eye on each side of your face is that each eye has a slightly dif-
ferent view of the world, which provides another binocular cue for depth perception called retinal
disparity.
Retinal disparity refers to a binocular depth cue that depends on the distance between the eyes. Because of

their different positions, each eye receives a slightly different image. The difference between the right and left eyes’

images is the retinal disparity. The brain interprets a large retinal disparity to mean a close object and a small retinal

disparity to mean a distant object.

e figure at the le shows how retinal disparity occurs: e difference between the image seen
by the le eye (1) and the one seen by the right eye (2) results in retinal disparity (3).
Another example of retinal disparity occurs when viewers wear
Photo Credit: center, © RubberBall/SuperStock special glasses to watch a 3-D movie, which has width, height, and
1. Left eye sees a depth. Standard 3-D glasses use a red and a green lens, which is a
slightly different technique to allow the right and le eyes to perceive slightly different
image of the fly.

2. Right eye 3. Brain com- views of the same scene. As a result, the brain receives two slightly
sees a slightly bines the two different images. As the brain automatically combines the slightly
different image slightly different different images, we get the feeling of depth—for example, seeing a
of the fly. images from left mad dog jump out of the movie screen into the audience (followed by
and right eyes and much screaming).
gives us a perception
of depth. Individuals who have only one eye still have depth perception
because there are a number of one-eyed, or monocular, cues for depth
perception, which we’ll explain next.

E . D E P T H P E R C E P T I O N 129

E. Depth Perception

Monocular (One Eye) Depth Cues

Could a A mythical creature called the Cyclops Cyclops or an individual with only one good eye could
had only one eye in the middle of his land an airplane because of monocular depth cues.
Cyclops land forehead. Although a Cyclops would Monocular depth cues are produced by signals from a

an airplane? lack depth perception cues associated single eye. Monocular cues most commonly arise from the

with retinal disparity, he would have I could land an way objects are arranged in the environment.
airplane with one eye!
depth perception cues associated with having one eye, or We’ll show you seven of the most common mono-
being monocular (mon means “one”). This means that a cular cues for perceiving depth.

Linear Interposition Photo Credits: top left, © Walter Bibikow/Getty Images; right, © Digital Stock Corporation; bottom left, © Digital Vision/Alamy
perspective makes you see
makes you the fish in front
see the road as closer and
as going on those in back as
forever. farther away.

1 Linear Perspective 3 Interposition

As you look down a long stretch of road, the parallel lines formed by the sides of As you look at the school of fish in the photo
the road appear to come together, or converge, at a distant point. is convergence above, you can easily perceive which fish are in
is a monocular cue for distance and is called linear perspective. front and which are in back, even though all the
fish are about the same size. You can identify and
Linear perspective is a monocular depth cue that results as parallel lines come point out which fish are closest to you and which
together, or converge, in the distance. are farthest away by using the monocular depth
cue of overlap, which is called interposition.
Relative size
makes you see Interposition is a monocular cue for depth percep-
the larger towers tion that comes into play when objects overlap. The
as closer and the overlapping object appears closer, and the object that
smaller towers is overlapped appears farther away.
as farther away.

2 Relative Size

You expect the electric towers in the photo above to be the same size. However,
since the electric towers in the front appear larger, you perceive them as closer,
while the electric towers in the back appear smaller and thus farther away. e
relative size of objects is a monocular cue for distance.

Relative size is a monocular cue for depth that results when we expect two objects to
be the same size and they are not. In that case, the larger of the two objects will appear
closer and the smaller will appear farther away.

130 M O D U L E 6 P E R C E P T I O N

Light makes the 6 Atmospheric Atmospheric
outlines of the perspective makes
footprints appear Perspective clear objects seem
closer, while One of the depth cues you nearer and hazy
shadow makes may have overlooked is cre- objects as being
the imprints seem ated by changes in the atmo- farther away.
farther away. sphere. For example, both the
Photo Credits: top left, © Stephen Firsch/Stock, Boston; top right, © Henry/Gamma Press; bottom left, © Photodisc/SuperStock; bottom right, man sitting on the chair and
© Robert Holmes/Corbis 4 Light and Shadow the edge of the cliff appear
much closer than the fog-
Notice how the brightly lit edges of the footprints shrouded hills and landscape
appear closer, while the shadowy imprint in the in the background. These
sand appears to recede. Also, the sunny side of the monocular depth cues are
sand dune seems closer, while the back side in created by changes in the
shadows appears farther away. The monocular atmosphere.
depth cues shown here involve the interplay of
light and shadows. Atmospheric perspective is
a monocular depth cue that is
Light and shadow make up monocular cues for depth created by the presence of dust,
perception: Brightly lit objects appear closer, while smog, clouds, or water vapor.
objects in shadows appear farther away. We perceive clearer objects as
being nearer, and we perceive
Texture gradient hazy or cloudy objects as being
makes you see the farther away.
sharply detailed,
cracked mud as 7 Motion Parallax Motion
being closer. parallax
In this photo, you makes
5 Texture Gradient can easily tell which blurry
riders seem closer objects
You can’t help but notice how the wide, detailed to you and which appear
surface cracks in the mud seem closer, while the appear farther away. closer
less detailed and narrower cracks appear farther That’s because you and clear
away. These sharp changes in surface details are perceive fast-moving objects
monocular depth cues created by texture gradients. or blurry objects appear
(horsemen on the farther
Texture gradient is a monocular depth cue in which away.
areas with sharp, detailed texture are interpreted as
being closer and those with less sharpness and poorer right) as being closer
detail are perceived as more distant. to you and slower-
moving or clearer
objects (horsemen on the le ) as being farther away. ese monocular depth
cues come from the way you perceive motion.
Motion parallax is a monocular depth cue based on the speed of moving objects.

We perceive objects that appear to be moving at high speed as closer to us than those

moving more slowly or appearing stationary.

We have just discussed seven monocular cues involved in perceiving depth
and distance accurately. Because they are monocular cues—needing only
one eye—it means that people with only one eye have depth perception good
enough to land a plane, drive a car, or play various sports such as baseball and
tennis. If you wish to try some of these monocular cues, just hold your hand
over one eye and see if you can avoid objects as you walk around a room.
We turn next to occasions where our perceptual system is fooled, and we
see things that are not there. Welcome to the world of illusions.

E . D E P T H P E R C E P T I O N 131

F. Illusions

Strange Perceptions An illusion is a perceptual experience in which you perceive an image

What is ere are two reasons that much of the time
your perceptions of cars, people, food, trees, as being so strangely distorted that, in reality, it cannot and does not exist.
an illusion? animals, furniture, and profes- An illusion is created by manipulating the perceptual cues so that

sors are reasonably accu- your brain can no longer correctly interpret space, size, and

rate reflections but, because of emotional, depth cues.

motivational, and cultural influences, never For example, if you look at the illustration to the
exact copies of reality. le , you’ll notice the orange circles are moving right
First, we inherit similar sensory systems before your eyes! You have to admit this is a fun
whose information is processed and inter- and impressive illusion. But how can the circles
preted by similar areas of the brain (Franz appear to be moving when it’s actually a still illus-
et al., 2000). However, damage to sensory tration? In this case, we do not know for sure. e
areas of the brain can result in very distorted illustration somehow activates motion-detecting
perceptions, such as the neglect syndrome neurons in the visual pathway. Patterns in illustra-
(p. 79), in which people do not perceive one tions like this one fool the visual system into seeing
side of their body or one side of their environ- motion when it doesn’t really exist (Ramachandran &
ment. The second reason our perceptions are Rogers-Ramachandran, 2007). e motor perception
reasonably accurate is that we learn from com- Eyes see circles moving in this area of the brain actually shows heightened activity as
mon experience about the sizes, shapes, and illustration, even when movement people move their eyes while looking at these types of
illusions (Kuriki et al., 2008). (If you cannot see the
doesn’t really exist!

colors of objects. But we’ve already discussed
how perceptions can be biased or distorted by previous emotional circles move, please don’t worry; some people with otherwise normal
and learning experiences, such as perceiving dogs differently a er vision cannot see movement in this illustration.)
being bitten by one. Now we come to another way that perceptions One of the oldest illusions that you have o en experienced is
can be distorted: by changing the actual perceptual cues so you the moon illusion, which also has proven very difficult to explain
perceive something unlikely, which is called an illusion. (H. E. Ross & Plug, 2002).

Moon Illusion

Moon appears to Moon appears 50% Photo Credits: left, © Robert P. Comport/Animals, Animals/Earth Sciences; right, © John Elk/Stock, Boston
be huge when it’s smaller when it’s
near the horizon. high in the sky.

e moon illusion has intrigued people for centuries because it of depth information. In contrast, because we view the elevated
is so impressive. e le photo shows that when a full moon is moon through empty space, there are no cues to indicate distance.
near the horizon, it appears (or gives the illusion of being) as
much as 50% larger than when it is high in the sky (right photo). us, our brains perceive the moon on the horizon to be farther
Here’s the interesting part: You perceive this 50% increase in size away than the elevated moon. Consequently, since the size of both
even though the size of both moons on your retinas is exactly moons on our retinas is exactly the same and the moon on the
the same. horizon is perceived as being farther away, our brain compensates
to correct this inconsistency by inflating our perception of the size
For over 50 years, researchers have proposed different theories of the moon on the horizon. Consistent with this theory, research-
for the moon illusion. Currently, no single theory can explain the ers found that subjects estimated the horizon moon to be much
moon illusion completely and it is believed that several factors farther away and interpreted its size as being larger. Likewise, sub-
contribute to it. e most important factor has to do with how the jects estimated the elevated moon to be closer and perceived it as
view of the landscape surrounding the moon influences our depth being smaller (L. Kaufman, 2000).
perception (H. E. Ross & Plug, 2002).
Besides naturally occurring illusions, there are others that
When we view the moon on the horizon, we see it in relation humans have created. One of the most interesting illusions comes
to the landscape (trees, mountains, buildings), which consists from looking inside the Ames room.

132 M O D U L E 6 P E R C E P T I O N

Ames Room

Adult woman appears In the Ames room (le photo), you perceive the boy on the right to be twice as
smaller than young boy. tall as the woman on the le . In fact, the boy is smaller than the woman but
appears larger because of the design of the Ames room.
The Ames room, named after its designer, shows that our perception of size can be

distorted by changing depth cues.

e reason the boy appears to be twice as tall as the woman is that the room
has a peculiar shape and you are looking in from a fixed peephole. To see how
the Ames room changes your depth cues, look at the diagram of the Ames room
in the drawing below right.
If you view the Ames room
from the fixed peephole, the
room appears rectangular
and matches your previous
experience with rooms, which are usually rectangular. However, as the right figure
shows, the Ames room is actually shaped in an odd way: e le corner is twice as far
away from the peephole as the right corner. is means that the woman is actually twice as
far away from you as the boy. However, the Ames room’s odd shape makes you think that you are
seeing the two people from the same distance, and this (illusion) makes the farther woman appear to be
shorter than the boy (Goldstein, 2010).
e next two illusions either change your perceptual cues or rely too much on your previous perceptual experiences.

Ponzo Illusion Müller-Lyer Illusion

Black The figures at the left
bars are and right illustrate the
the same Müller-Lyer illusion.
length. Notice that the left
arrow appears notice-
In the figure above, the top black bar appears ably shorter than the
Photo Credits: top left, © Baron Wolman/Woodfin Camp & Associates; center right, Craig McClain to be much longer than the bottom black right arrow. However, Left and
bar. However, if you measure these two bars, if you measure them, right
you will discover that they are exactly the you’ll prove that the arrows
same size. is is the Ponzo illusion. I clear- arrows are of equal are the
ly remember measuring the first time I saw same
this picture because I couldn’t believe the
bars were the same size. You perceive the length.
top bar as being farther away, and you have
learned from experience that if two objects length.
appear to be the same size but one is farther One explanation for
away, the more distant object must be larger; this illusion is that you are relying on size cues learned
thus, the top bar appears longer. from your previous experience with corners of rooms.
You have learned that if a corner of a room extends
outward, it is closer; this experience distorts your perception so that the left arrow
appears to be shorter. In contrast, you have learned that if a corner of a room recedes
inward, it is farther away, and this experience makes you perceive the right arrow as
longer (Goldstein, 2010). Illusions are fun, but what have we learned?

Learning from Illusions

Most of the time, you perceive the world with reasonable accuracy by using a set of
proven perceptual cues for size, shape, and depth. However, illusions teach us that
when proven perceptual cues are changed or manipulated, our reliable perceptual pro-
cesses can be deceived, and we see something unreal or an illusion. Illusions also teach
us that perception is a very active process, in which we continually rely on and apply
previous experiences with objects when we perceive new situations. For example, you’ll
discover later (p. 140) how the entertainment industry changes the perceptual rule of
closure to create movies, whose motion is a brilliant illusion. A er the Concept Review,
we’ll discuss a form of perception that the U.S. Congress almost outlawed.

F. I L L U S I O N S 133

Concept Review

1. This figure illustrates the concept of 10. In this figure, you see a continuous line
the , which is defined as from A to B, rather than a line from A to C,
the intensity level of a stimulus such that following the rule.
a person will have a 50% chance of detecting it.

2. The smallest increase or 11. Although physical qualities of stimuli may
decrease in the intensity of a change, you may perceive them as remaining
stimulus that a person can detect the same because of (a) . For
is called a (a) . example, as a car drives away from you, its
The increase in intensity of a image on your retina becomes smaller but you
stimulus needed to produce a just know that the car does not shrink in size
noticeable difference grows in proportion to the intensity of the because of (b) constancy.
initial stimulus; this is called (b) law. When you close a door, its shape on your reti-
na changes from a rectangle to a trapezoid, but
3. Our first awareness of sensory infor- you perceive the door as remaining the same
mation, in the form of meaningless because of (c) constancy. If you had a bright red
bits of information, is called a car, it would appear red in bright light and still appear to be red in
(a) . When many bits dimmer light because of (d) constancy.
of sensory information have been assem-
bled into a meaningful image, it is called 12. Cues for depth perception that depend on
a (b) , which can be both eyes are called (a) cues.
biased or distorted by our unique set of experiences. Cues for depth perception that depend on a
single eye are called (b) cues.
4. Early psychologists discovered a set of The binocular cue that occurs when your eyes Photo Credits: (#3) Custom Medical Stock Photo; (#4) Painting by Richard Haas, photo © Bill Horsman; (#13) © Photodisc/SuperStock
rules or principles that our brains use to auto-
matically group or arrange stimuli into percep- move inward to track a fly landing on your
nose is called (c) . The binoc-
tual experiences. These early researchers, who ular cue that occurs when each eye receives a slightly different
were called psychologists,
disagreed with other early psychologists, who image is called (d) .

were called structuralists. 13. Monocular cues for depth perception
include: cues from overlapping objects, called
5. You automatically separate an image into (a) ; cues from two parallel
a more dominant, detailed figure and a less lines converging, called (b) ;
detailed background according to the cues from larger and smaller images, called
(c) ; cues from the presence of
rule.

7. You see this dust and smog, called (d) ; and
6. You fill in missing image as formed cues from nearer and farther objects moving at
parts to form a complete by an oval and an different speeds, called (e) .
image as a result of overlying square because of
the the rule. 14. If perceptual cues are so changed that our
rule. brains can no longer interpret them correctly,
9. In this figure, you we perceive a distorted image of reality, called
see a blue numeral an (a) . Such a distorted
8. You divide 2 instead of light perception illustrates that perception is an
each line of this and dark blue active process and that we rely on previous
figure into sepa- (b) when perceiving new
rate groups of circles because of the situations.
objects according rule.
to the
rule.

Answers: 1. absolute threshold; 2. (a) just noticeable difference, (b) Weber’s; 3. (a) sensation, (b) perception; 4. Gestalt; 5. figure-ground;
6. closure; 7. simplicity; 8. proximity; 9. similarity; 10. continuity; 11. (a) perceptual constancy, (b) size, (c) shape, (d) color; 12. (a) binocular,
(b) monocular, (c) convergence, (d) retinal disparity; 13. (a) interposition, (b) linear perspective, (c) relative size, (d) atmospheric perspective,
(e) motion parallax; 14. (a) illusion, (b) experiences

134 M O D U L E 6 P E R C E P T I O N

G. Research Focus: Influencing Perception

Can “Unsensed Messages” Change Behavior?

Why did Sometimes research questions come from unusual places—in this case, a movie theater. In Eat
people buy the late 1950s, moviegoers were reported to have bought 50% more popcorn and 18% more
Coca-Cola when the words “Eat popcorn” and “Drink Coca-Cola” were projected sublimi-
more popcorn? nally (1/3,000 of a second) during the regular movie (J. V. McConnell et al., 1958). Researchers popcorn!
recently found the first physiological evidence that subliminal images attract the brain’s
attention on a subconscious level. People’s brains responded to subliminal images even when they were not conscious
of having seen them (Bahrami et al., 2007). As impressive as these results sound, the study did not examine whether subliminal images
could influence thought or behavior. Even so, many advertisers now claim that subliminal messages can change specific behaviors.

Changing Specific Behaviors Influencing Perceptions

At the beginning of this module, we told you about Maria, who, like mil- Is it possible to have biased attitudes and be unaware of hav-
lions of other Americans, bought an audio CD because it claimed to con- ing them? If so, can these unknown or unconscious attitudes
tain subliminal persuasion that would effortlessly change her behavior. influence our perceptions? These questions are similar to
A subliminal message is a brief auditory or visual message that is presented those Mahzarin Banaji, a researcher at Harvard, has been
asking for many years now. In one very interesting study, she
below the absolute threshold, which means that there is less than a 50% chance wanted to determine whether people’s expectations could
unknowingly influence their perceptions (Vedantam, 2005).
that the message will be perceived.
Method. Fi y business executives viewed a black-and-
To answer the research question, Can subliminal messages change white video clip of a basketball game in which the players
specific behaviors?, researchers conducted a well-designed experiment were making quick passes and rapidly changing positions.
that used a double-blind procedure. The executives were asked to count the number of passes
Method. For several weeks, subjects listened made during the video clip. When the video clip ended,
to two different recordings titled either “Improve executives excitedly shouted out answers.
Self-Esteem” or “Improve Memory.” Then they However, Banaji was not interested
rated any improvement in these behaviors. in their answers and instead asked
Double-blind procedure. Researchers had whether anyone had seen anything
to control for any possible placebo effects, such unusual. The video watched by
as subjects showing improvement because they the executives did in fact show something
believed they were hearing powerful subliminal unusual; about halfway through the video, a
Labels did not match messages. Therefore, subjects woman with an open white umbrella slowly
subliminal messages. were not told which sublimi- walked through the screen from one end to
the other. How many of the executives do
nal messages the recordings contained. For exam- you think noticed something so obvious?
ple, some recordings labeled “Improve Memory”
contained subliminal messages for improving Results. It turns out that none of the fifty executives
memory, while others contained subliminal mes- noticed the woman with the white umbrella. Banaji played
sages for improving self-esteem. us, because of the the video clip for the executives again and this time told
double-blind procedure, subjects were unaware of them not to pay attention to the basketball passes. When the
Photo Credits: center right, © Peter Glass/Alamy; top right, PhotoDisc, Inc. the fact that some recordings’ subliminal mes- But, subjects believed woman appeared, the executives could not believe they had
sages did not match the recordings’ labels. what the labels said. not noticed something so obvious and worried that hidden
biases could influence them in other ways.
Results. About 50% of subjects reported improvements in either self-
esteem or memory. However, subjects reported improvements in behavior These results indicate that people’s expectations can
based on what the recordings’ labels promised rather than on what the unknowingly or subliminally influence their perceptions.
subliminal messages were. For example, a subject who listened to a record- Other research has also shown that subtle cues o en influ-
ing labeled “Improve Self-Esteem” reported improvements in self-esteem ence people without their awareness. Several studies focused
even though the recording contained subliminal messages for improving on racial biases found that even when people genuinely deny
memory. ese results suggest a self-fulfilling prophecy at work. having racial biases, results reveal that they hold biased
Self-fulfilling prophecies involve having strong beliefs about changing some racial attitudes without their awareness. Thus, people’s
unconscious attitudes can unknowingly influence their
behavior and then acting, unknowingly, to change that behavior. behaviors and potentially influence the way people make
important decisions, such as those made in the hiring pro-
Researchers concluded that subliminal messages in self-help record- cess or in court trials or even in critical medical situations
ings did not affect the behavior they were designed to change. Instead, (S. Carpenter, 2008; Lehrman, 2006; Vedantam, 2005).
any changes in behavior resulted from listeners’ beliefs that the record-
ings would be effective (Epley et al., 1999). Most research, in fact, sug- Next, you’ll see how cultural values and experiences can
gests that subliminal messages cannot change our behaviors in any also unknowingly change what you perceive.
significant way (Dijksterhuis et al., 2007; Greenwald et al., 2002). G . R E S E A R C H F O C U S : I N F L U E N C I N G P E R C E P T I O N 135
ere is evidence, however, that unconscious attitudes can unknow-
ingly or subliminally influence perception.

H. Cultural Diversity: Influence on Perceptions

What Do Cultural Influences Do? What if you were raised No one doubts that cultural influences affect the
in a different culture? way people eat, dress, talk, and socialize. But you are
If you visit ethnic sections of large U.S. cities, such as less likely to notice how cultural influences also affect
Chinatown or Little Italy, or visit foreign countries, how you perceive things in your own environment.
you become aware of cultural differences and influ-
ences. For example, this photo shows two Japanese For example, cultural anthropologists, who study
women in traditional robes and setting, which symbol- behaviors in natural settings in other cultures, have
ize the different cultural influences of Japan compared reported intriguing examples of how cultural expe-
to Western countries. riences influence perceptual processes. We’ll begin
with a remarkable finding about the role of cultural
Cultural influences are persuasive pressures that influences in how people recognize faces.
encourage members of a particular society or ethnic group to

conform to shared behaviors, values, and beliefs.

Perception of Faces the faces they looked at were of
It is generally believed that basic visual processes, such
as recognizing faces, are common to all people, Western Caucasian or East Asian
regardless of their culture. People all around the world males (Blais et al., 2008).
are able to quickly recognize whether a face is familiar One possible explanation for
or not, but new research shows that people’s culture the cultural differences in how Photo Credits: top, © Ric Ergenbright/Corbis; center, Courtesy of Roberto Caldara; bottom, By courtesy of Takahiko Masuda and Dr. Richard Nisbett,
influences the process they use to recognize faces. people perceive faces has to do University of Michigan
Researchers recorded eye movements of Western with the value placed on eye con-
Caucasians (English, French, German) and East tact. Eye contact is important in
Asians (Chinese, Japanese) while they looked at Western culture but inappropri-
Western Caucasian and East Asian faces. e results Western Caucasians focused mostly on the eyes ate and even improper in many
showed that the eye movements of Western Caucasians and mouth (red areas), whereas East Asians Asian cultures. It is possible that
followed a triangular pattern, focusing on the eyes and focused mostly on the nose (blue areas). Asians are taught to recognize

mouth (see red areas in right photos), whereas East Asians looked faces without looking into others’ eyes (Blais et al., 2008).
at only the central region of faces, focusing mostly on the nose How we describe images is another example of how culture
(see blue areas in le photos). e results were the same whether influences what we perceive.

Perception of Images
Please look at the photo below for a few seconds and then close relationship between objects and backgrounds, which is called
your eyes and describe what you saw. Richard Nisbett (2000) and holistic thinking—seeing a forest and thinking about how trees
colleagues found that what you see or think about depends, to a combine to make up a forest (Chua et al., 2005).
large extent, on your culture. ese differences in thinking and perceiving (ana-
For example, a er looking at the under- Look at the photo briefly and then lytical versus holistic) have been thought to primarily
water scene, Americans tended to begin close your eyes and describe it. come from differences in culture, including social and

their descriptions by focusing on the largest religious practices, languages, and even geography
fish and making statements like “ ere was (Nisbett, 2007; Nisbett & Miyamoto, 2005). Research
what looked like a trout swimming to the has even shown that an individual’s cultural back-
le .” Americans are more likely to zero in ground influences brain activity during simple tasks.
on the biggest fish, the brightest object, the For instance, one study involved two tasks assigned
fish moving the fastest. to East Asians and Americans. In one task, people
Compared to Americans, Japanese sub- estimated the length of a line—an easier task for
jects were much more likely to begin by Americans. In another, they estimated the line’s length
setting the scene, saying, for example, “ e relative to the size of a square—an easier task for East
bottom was rocky.” On average, Japanese subjects made 70% more Asians. Even though no difference in performance was found
statements about how the background looked than Americans did between the two groups, the level of brain activity differed, sug-
and twice as many statements about the relationships between the gesting varying amounts of effort. Brain activity was greater for the
fish and the backgrounds. For instance, Japanese subjects were tasks each group found to be more difficult (Hedden et al., 2008).
more likely to say, “ e big fish swam past the gray seaweed.” us, cultural differences in people’s perceptions are based not
Generally, Americans analyze objects separately, which is called only on differences in thinking and perceiving, but also on actual
analytical thinking—seeing a forest and focusing more on sepa- differences found in the brain.
rate trees. In comparison, Easterners tend to think more about the Cultures also influence how we see cartoons.

136 M O D U L E 6 P E R C E P T I O N

Perception of Motion

For just a moment, look at the picture of the dog (below) and However, people from non-Western
notice what its tail is doing. en look at the female figure (right) cultures, who have no experience with
and describe what the figure is doing. Most people in Western these pictures, do not perceive the
cultures immediately perceive what is dog’s tail or the figure as moving. Non-
happening: the dog is wagging its tail, and Westerners see only an unusual dog that
the figure is spinning. Because of our has three tails and a strange figure that is
Western cultural experience with pictures, surrounded by circles; they do not perceive
we have learned to recognize that certain any indication of movement in these drawings
kinds of repeated images (the dog’s tail) and (S. Friedman & Stevenson, 1980). is is a per-
certain lines and circles (the dancing fig- fect example of how Western cultural influences
What is the dog’s ure) indicate movement. We have learned shape our perceptions, o en without our realizing.
tail doing? and become so accustomed to seeing these
If part of your cultural experience involves see-
kinds of pictures indicate motion that the tail and the dancer ing 3-dimensional objects in books, you won’t be What is this
able to draw the next figure. dancer doing?

really do seem to be in motion.

Photo Credits: center, © Digital Stock Corporation; right, © Peter Beavis/The Image Bank/Getty Images Perception of 3 Dimensions Perception of Beauty Perceptual Sets

Can you draw this impossible figure? Do you think this woman is attractive? Do you think this muscular body is beautiful?

Earlier in this module, we talked about In the past, when Burmese girls were From our previous
illusions. e above figure is an example about 5 years old, they put a brass cultural experiences
of an illusion. You will find that if you coil one-third-inch wide around with images and
look at the right end of this tuning fork, it their necks. As they grew older, girls objects, we develop
appears to have two prongs. But if you added more brass coils until they certain expectations
look at the left end, it appears to have had from 19 to 25 wrapped around about how things should
three prongs. You’re looking at a figure their necks, sometimes weighing be; these expectations are
that most of us cannot draw because it over 10 pounds. e appearance of called perceptual sets.
seems impossible. long necks, caused by the brass coils,
was perceived as being very attrac- Perceptual sets are
An impossible figure is a perceptual expe- tive by Burmese people, who live in learned expectations that
rience in which a drawing seems to defy basic southeast Asia. is custom eventu- are based on our personal,
geometric laws. ally declined as neck coils were no social, or cultural experi-
longer considered beautiful, just ences. These expecta-
As you look at it, it changes almost mag- cruel and uncomfortable. Recently, tions automatically add
ically back and forth from a two-pronged however, the custom has been information, meaning, or
to a three-pronged tuning fork. e illusion revived because now tourists come feelings to our perceptions
is that the middle fork is unreal because it and pay about $6 to see and take and thus change or bias
seems to come out of nowhere. photos of women with brass neck our perceptions.
coils (Moe & Son, 2005).
When people from industrialized For example, as you look at this bodybuilder,
nations try to draw this figure from is example illustrates how cul- you automatically add personal feelings, such as
memory, they almost surely fail. What is tural values influence our percep- like/dislike and approve/disapprove, as well as
interesting is that Africans who have no tions of personal beauty. impressions of physical characteristics: height,
formal education do not see any illusion about 6 feet, and weight, about 225 pounds.
but perceive only a two-dimensional pat- Because of your perceptual set for bodybuilders,
tern of flat lines, which they find easy to you expect them to be large, and so you will be
draw from memory. In contrast, people surprised to learn that this bodybuilder is only
with formal education, who have spent 5 feet 2 inches tall and weighs 182 pounds. One
years looking at three-dimensional rep- function of perceptual sets is to automatically fill
resentations in books, perceive this object in information or add feelings that can greatly
as having three dimensions, a pattern that modify our perceptions.
is almost impossible to draw (Coren &
Ward, 1993). ese examples show that we rarely perceive the
world exactly as it is. Rather, our perceptions can
be changed, biased, or distorted by experiences,
such as cultural influences and perceptual sets.

Next, we’ll discuss a controversial kind of
perception that goes by the initials ESP.

H . C U L T U R A L D I V E R S I T Y : I N F L U E N C E O N P E R C E P T I O N S 137

I. ESP: Extrasensory Perception

Definition and Controversy

What are No one doubts your ability to receive infor- researchers demand hard, scientific evidence rather than evidence
mation through one or more of your major from testimonials (p. 30), which are based on personal beliefs or
psychic powers? senses—seeing, hearing, tasting, smelling, experiences and have a high potential for error and bias. ere
and touching—because this ability has been are many examples of testimonials that, when evaluated with
repeatedly demonstrated and reliably measured. In comparison, most scientifically designed experiments, were found to be unproven.
research psychologists do not believe you can receive information Questioning testimonial evidence applies especially to ESP,
outside normal sensory channels, which is called which is outside normal senses, defies physical
extrasensory perception, because this phe- and biological explanations, and stretches the
nomenon has been neither repeatedly laws of physics (P. Kurtz, 1995; Nisbet, 1998).
demonstrated nor reliably measured Researchers have been studying the brain to
(D. J. Bem & Honorton, 1994). better understand ESP. In one study, two groups
Extrasensory perception (ESP) is a group of psychic of people, believers and nonbelievers in ESP,
Psi refers were shown rapidly displayed images of real
experiences that involve perceiving or sending information to getting faces and scrambled faces as well as real words
information by
(images) outside normal sensory processes or channels. methods that and nonwords (Begley, 2007c). eir task was
defy the laws to identify real faces and words. Nonbelievers
ESP includes four general abilities—telepathy, pre- of physics. identified more real faces as scrambled faces
cognition, clairvoyance, and psychokinesis.
and more real words as nonwords than believ-
Telepathy is the ability to transfer one’s thoughts to another ers in ESP. Even more fascinating is that when
or to read the thoughts of others. Precognition is the ability to these nonbelievers in ESP were given a drug that
foretell events. Clairvoyance is the ability to perceive events or increases levels of the neurotransmitter dopamine, they identi-
objects that are out of sight. Psychokinesis is the ability to exert mind fied more faces and words as real, even those that weren’t. It turns
over matter—for example, by moving objects without touching them. out that having more of a neurotransmitter found in all of our
brains may make us more likely to believe in the supernatural!
Together, these extrasensory perceptions are called psi phenomena.
The term psi refers to the processing of information or transfer of energy
by methods that have no known physical or biological mechanisms and that

seem to stretch the laws of physics. Another reason researchers demand reliable and repeatable
According to the Gallup polls, 41% of adult Americans believe in evidence to prove the existence of ESP is that some demonstra-
tions of psi phenomena have involved trickery or questionable
ESP, 31% believe in communication between minds without the use of methodology. For example, one well-known researcher has
regular senses, 21% believe they can communicate mentally with some- used trickery and magic to duplicate many of the better-known
one who has died, and as many as 55% believe in psychics (D. W.Moore, demonstrations of ESP, such as mentally bending spoons, mov-
2005). In fact, only 7–10% of Americans do not believe in any of these ing objects, and reading messages in sealed envelopes. This
extrasensory perceptions (Begley, 2007c, 2008c). e reason so many researcher’s name is the Amazing Randi.
Americans but so few research psychologists believe in ESP is that

Trickery and Magic
According to James Randi, known as the Many years ago, a television show under the supervision of
Could you Amazing Randi (below photo), and others James Randi offered $100,000 to anyone who could demonstrate

spot a trick? acquainted with magic, much of what passes psychic powers. Twelve people claimed to have psychic powers,
for extrasensory perception is actually done such as identifying through interviews the astrological signs under
through trickery (Randi, 2005, 2009; Ybarra, 1991). For which people were born, seeing the auras of people standing
example, to show how easily people may be fooled, behind screens, and correctly reading Zener cards (show-
Randi sent two young magicians to a lab that stud- ing five symbols: square, circle, wavy lines, plus sign, and
ied psychic phenomena. Instead of admitting star). Of the 12 people who claimed psychic powers, Photo Credit: bottom, © Jeffery Allan Salter/Corbis
they were magicians, the pair claimed to have none scored above chance on any of these tasks
psychic powers and to perform psychic (Steiner, 1989). Although people may claim psy-
feats, such as mentally bending keys and chic powers, most cannot demonstrate such pow-
making images on film. A er 120 hours of ers under controlled conditions, which eliminate
testing, the lab’s researchers, who had trickery, magic, and educated guessing. On the
carefully conducted and supervised the next page, we’ll learn how one popular TV psychic
ESP demonstrations, concluded that the responded to being asked to take James Randi’s
two did indeed have genuine psychic abili- test to prove she had psychic powers.
ties. e lab’s researchers were not expect- To eliminate any trickery, claims of psychic
ing trickery, had not taken steps to prevent abilities must withstand the scrutiny of scientific
The Amazing Randi, professional
magician, shows people how ESP is
it, and were thus totally fooled into believ- done through trickery. investigation. Let’s see how a controlled ESP
ing they were witnessing ESP. experiment is designed and conducted.

138 M O D U L E 6 P E R C E P T I O N

ESP Experiment

How do One of the more common dem- In the Ganzfeld procedure, the
onstrations of psychic ability is receiver is placed in a reclining
researchers to use Zener cards, which show chair in an acoustically isolated
study psychic f ive sy mbols—circle, waves, room. Translucent ping-pong ball
abilities? square, plus sign, and star (on halves are taped over the eyes, and
right). A researcher holds up the headphones are placed over the
back of one card and asks the subject to guess the sym- ears. e sender, who is isolated in
bol on the front. If there were 100 trials, the subject a separate soundproof room, con-
could identify 20 symbols correctly simply by guessing centrates for about 30 minutes on a Ganzfeld procedure involves
(chance level). However, if a subject identifies 25 sym- target, which is a randomly selected mentally sending this picture to
bols correctly, which is above chance level, does that visual stimulus, such as a photo or
a person in another room.

mean the subject has psychic powers? is is a simpli- art print (right figure). At the end of this period, the receiver is shown
fied example of a very complicated statistical question: four different stimuli and asked which one most closely matches
How can we determine whether a person has psychic what the receiver was imagining. Because there are four stimuli, the
powers or is just guessing correctly? erefore, to solve receiver will guess the target correctly 25% of the time. us, if the
one major problem in psi research—how to eliminate receiver correctly identifies the target more than 25% of the time,
guesswork and trickery—researchers use a state-of- it is above chance level and indicates something else is occurring,
the-art method called the Ganzfeld procedure. perhaps extrasensory perception (D. J. Bem & Honorton, 1994).
The Ganzfeld procedure is a controlled method for We have described the Ganzfeld procedure in detail to illustrate

eliminating trickery, error, and bias while testing telepath- Symbols the precautions and scientific methodology that researchers must use
used to
ic communication between a sender—the person who study to rule out the potential for trickery, error, and bias. e next ques-

sends the message—and a receiver—the person who ESP tion is perhaps the most interesting of all: What have researchers

receives the message. learned from recent Ganzfeld experiments?

Status of ESP and TV Psychics

What is e history of psychic research is filled with 2001). One of the biggest problems with ESP is that those who
controversy, especially about replication, claim to have it are rarely subjected to scientific study. Such is the
the scientific which is the ability of other researchers to do case with so-called psychic hotlines.
status of ESP? similar experiments and obtain similar Television psychics. ere is no test or training for becoming a
results. For example, Daryl Bem and Charles psychic, so anyone can claim to be one. Many alleged TV psychics
Honorton (1994), two respected researchers, reported that the were recruited through want ads and paid $15 to $20 an hour to
Ganzfeld procedure (described above) provided evidence for men- answer questions from
tal telepathy; that is, one person mentally transferred information strangers (Nisbet, 1998).
to a person in another room. e biggest question about Bem and TV psychics have been so
Honorton’s controversial mental telepathy results was whether popular that at one time
their findings could be repeated or replicated by other researchers. they took in $100 million
Importance of replication. Science has a powerful weapon for a year.
evaluating research findings, called replication, that simply says: Sylvia Browne is a
If other scientists cannot repeat well-known TV psychic
the results, the results prob- who has become a multi-
ably occurred by chance. millionaire by writing
More recently, researchers books, providing psychic TV psychic Sylvia Browne refuses to take a
controlled test to prove her psychic powers.

evaluated the results of readings in person (cost
30 Ganzfeld experiments conducted $700) and over the phone (cost $200), and making regular appear-
by 7 independent researchers. These ances on e Montel Williams Show, where she gives advice and
researchers reported that the original claims to connect viewers with their loved ones who have died.
Photo Credit: top right, © Corel Gallery Ganzfeld finding, which supported Sylvia Browne has been repeatedly asked by the Amazing Randi
some kind of mental telepathy, could to take his controlled test to prove she has psychic powers. Despite
not be replicated (Milton & Wiseman, agreeing on national TV that she would do so, now years later she
1999). This failure to replicate the has yet to take the test (R. Friedman, 2006; Randi, 2008). There
Ganzfeld experiments, which represent is no scientific evidence that self-proclaimed psychics are better
the best-controlled studies on ESP to date, at knowing or predicting the future than would occur by chance
The best-known means that there is currently little or no reli- (Sheaffer, 1997).
mental telepathy
results could not able scientific evidence to support the existence Next, we’ll discuss several other forms of perceptions that fool
be replicated. of ESP or psi phenomena (Milton & Wiseman, our senses into believing that fixed things are moving.

I . E S P : E X T R A S E N S O R Y P E R C E P T I O N 139

J. Application: Creating Perceptions

Can we About 20,000 years ago, early humans (Homo sapiens) created some of the
earliest images by using earth pigments to paint prancing horses on the sides
create new of their caves (right photo) (S. Fritz, 1995). About 3,000 years ago, Egyptians
perceptions? created some of the most impressive images with their enormous and long-
lasting pyramids. Today, computer researchers are using virtual reality tech-
niques to develop new images and perceptions that can put you in the middle of a mind-blowing
three-dimensional world. We’ll begin our look at how perceptions are created with an old perceptual
device that is used in modern billboards. Painted 20,000 years ago

Creating Movement Phi movement refers to the illusion that lights that are actually station-

e father of the flashing lights used in today’s billboards, movie
marquees, and traffic arrows was a distinguished Gestalt psycholo- ary seem to be moving. This illusory movement, which today is called
gist named Max Wertheimer. In the early 1900s, Wertheimer spent apparent motion, is created by flashing closely positioned stationary lights
a considerable amount of time in a darkened room, where he at regular intervals.
experimented with flashing first one Each time you pass a traffic arrow composed of flashing
light and then a second light that was lights or perceive a moving string of lights used in an
positioned some distance away. He dis- advertising sign, you are seeing a practical application of
covered that if the time between flash- Wertheimer’s phi movement. This phi movement was one
ing one light and then the other was of the first examples of how ordinary visual stimuli could be
adjusted just right, the two flashes were adjusted to create an illusion.
actually perceived as a moving spot of Another example of creating wonderful moving illusions
light rather than as two separate flashes. Neon billboards use flashing lights with stationary visual stimuli came from the remarkable genius
He called this illusion phi movement. to create the illusion of movement. of omas Edison, who invented motion pictures in 1893.

Creating Movies

Movies create the illusion of motion
by showing a series of fixed images.

If you attend a track meet and watch a 100-meter race and then, Beginning on the left side of the photo, notice that each frame Photo Credits: top right, © Gianni Dagli Orti/Corbis; center,
minutes later, watch a videotaped replay of the same race, you per- shows only a slight change in the position of the runner’s body. © PhotoDisc, Inc.; bottom, © Globus Brothers
ceive motion produced in two very different ways. One kind of However, if these frames were presented rapidly—for example, at
motion is real, while the other is an illusion. the movie standard of 24 frames per second—you would perceive
the illusion of an athlete running down the track.
Real motion refers to your perception of any stimulus or object that
actually moves in space. In a series of ingenious experiments, researchers discovered that
several complex mechanisms built into our visual system detect
As you watch a live 100-meter race, you are perceiving real cues that produce the illusion of motion (Ramachandran & Anstis,
motion. However, when you watch a replay of that same race, you 1986). One such cue is the closure principle, which means that our
are seeing apparent motion. brains fill in the motion expected to occur between images that
vary only slightly in position and are presented in rapid sequence.
Apparent motion refers to an illusion that a stimulus or object is mov- Without apparent motion, there would be no movies, television, or
ing in space when, in fact, the stimulus or object is stationary. The illusion flip books.

of apparent motion is created by rapidly showing a series of stationary Currently, researchers have developed a procedure that creates
a three-dimensional perceptual experience of walking through a
images, each of which has a slightly different position or posture than the house, dissecting a frog, or doing complicated human surgery. is
is the brave new world of virtual reality.
one before.
e principle for creating apparent motion is deceptively simple

and can be easily discovered by examining the positions of the
runner’s body in each frame of the time-lapse photo shown above.

140 M O D U L E 6 P E R C E P T I O N

Creating Virtual Reality Psychotherapy. In a psychologi-

What is a The invention of the movie camera was revolutionary cal application of virtual reality,
surgical because it created a new perceptual experience: the illu- clients with such fears as spiders,
sion that still pictures moved. Currently, another per-
robot? ceptual revolution is under way, and it’s called virtual flying, or heights are exposed

reality. to the feared stimuli in a three-
Virtual reality refers to a perceptual experience of being inside an object, mov- dimensional environment where

ing through an environment, or carrying out some action that is created or simulated everything appears very real.

by computer. In this photo, a client is Therapists use virtual
being treated for fear of spiders. reality to treat phobias
Remote and robotic surgery. In a medical application of virtual reality, She wears a plastic helmet that
surgeons can now practice their skills with surgical simulators on virtual (fear of spiders).
cadavers. Research shows that the use of virtual reality significantly improves contains a computer monitor
surgeons’ skills, reduces their error rates, and brings reduced pain and quick- that puts her inside a virtual reality kitchen in which
er recovery for patients (Dellorto, 2008; Science Daily, 2008). Virtual reality she sees, touches, and kills spiders. For example, Joanne
is also being used on real patients. For example, a surgeon can insert and Cartwright suffered a debilitating fear of spiders. “I
maneuver a tiny camera and surgical tools in patients through pencil-thin washed my truck every night before I went to work in
Photo Credits: top right, Ames Research Center/NASA, photo by Walt Sisler; left, 2000 Computer Motion Photograph by Bobbi Bennett altered by John MacNeill. incisions. e surgeon operates by maneuvering robotic arms (photo below), case there were webs,” she said. “I put all my clothes in
Reprinted with permission from John MacNeill; top center, © David Livingston/Getty Images; bottom center, © Robert Zuckerman/Time & Life Pictures/Getty Images which are steadier and more precise than human arms. Robotic surgery has plastic bags and taped duct tape around my doors so spi-
already been performed more than 70,000 times in many procedures, includ- ders couldn’t get in. I thought I was going to have a men-
ing the removal of prostate cancers and tal breakdown” (Robbins, 2000, p. D6). A er receiving
brain tumors, as well as heart surgery, 12 virtual reality sessions to decrease her fear, Joanne
middle-ear surgery, and pediatric sur- said, “I’m amazed because I am doing all this stuff I
geries (Berlinger, 2006; Dellorto, 2008; could never do—camping, hunting and hiking” (Carlin,
J. Fox, 2005; “Medical robot,” 2002). 2000). Psychotherapists report success in using virtual
Another truly amazing advance in surgi- reality therapy to treat a wide variety of phobias, post-
cal technology is the ability for a surgeon traumatic stress disorder (PTSD) (see p. 491), and drug
to perform remote surgery using a robot addictions (Bergfield, 2006; Mozes, 2008; Rizzo, 2006; Z.
(Berlinger, 2006). For instance, one sur- Rosenthal, 2007).
geon in New York robotically removed e next topic focuses on how much your first impres-
Doctors use virtual reality to guide a gallbladder from a patient in France sions of other people depend on your perceptions of their
a robot to perform operations. with no complications! physical appearances.

Creating First Impressions
Social psychologists have discovered family (mom, dad, and daughter), all of whom are
What’s your that facial features have a signifi- White. The Wurgel family participated in a TV
reality series called Black.White. and underwent
impression of the cant effect on our first impres- elaborate makeup transformations to change
White and Black sions and perceptions of people. their racial complexions (Associated Press,
family pictures? For example, we tend to per- 2006b; Gliatto, 2006; Patterson, 2006). The
ceive an attractive person real pictures of the Wurgel family are on the
as being interesting, sociable, intelligent, outgoing, top, and their transformation pictures are on
and kind (Lemley, 2000). Similarly, first impressions the bottom!
are also influenced by racial stereotypes, both positive Now that you have seen the dramatic
and negative, based on physical features such as skin effect race can have on our impressions of
color and hairstyle. Hollywood hair stylists know very others, you can judge for yourself how skin
well that the kind, amount, color, and style of actors’ color influences your perceptions of others.
hair can radically change their appearance and our We’ll discuss how we perceive people and form
impressions of them. Besides hair color and style, impressions in Module 25.
skin color has a considerable impact on first percep- The factors involved in forming first
tions and impressions. impressions as well as in creating moving
To illustrate how skin color can greatly change lights, movies, and virtual reality illustrate
your perceptions of people, please look at the two an important underlying principle of
photos on the right and think about your first perception: Our perceptions, which may
impressions of each person. Did you notice any- be changed or biased by personal experi-
thing peculiar about the two pictures? You’ll ences, are interpretations rather than exact
likely be surprised to learn the two pictures show copies of reality.
the same people. Both pictures are of the Wurgel
J . A P P L I C A T I O N : C R E A T I N G P E R C E P T I O N S 141

Summary Test

A. Perceptual Thresholds C. Rules of Organization

1. We discussed three basic questions 5. Many of the rules of perceptual organization
that psychologists ask about perception. involve ways of grouping or arranging stimuli.
Our first question—At what point are we According to one of these rules, the first thing
aware of a stimulus?— can be answered we do is automatically separate an image into
by measuring the threshold of a stimulus, two parts: the more detailed feature of an image
which is a point above which a stimulus becomes the (a) and the less
is perceived and below which it is not. detailed aspects become the (b) .
The intensity level at which a person has According to the (c) rule, stimuli tend to be
a 50% chance of perceiving the stimulus organized in the most basic, elementary way. According to the
is called the . (d) rule, stimuli that appear the same tend to
be grouped together. According to the (e) rule,
2. Our second question—At what point do we know a stimulus stimuli that are near one another tend to be grouped together.
intensity has increased or decreased?—can be answered by mea-
suring the smallest increase or decrease in the intensity of a stim- According to the (f) rule, stimuli that are
arranged in a smooth line or curve tend to be perceived as
ulus that a person can detect; this is called a (a) . forming a continuous path. According to the (g)
It has been found that the increase in stimulus intensity needed to
produce a just noticeable difference increases in proportion to the rule, we tend to fill in the missing parts of a figure and perceive it
as complete.
intensity of the initial stimulus; this is called (b)
law.
D. Perceptual Constancy

B. Sensation Versus Perception 6. Although the size, shape, brightness, and
color of objects are constantly changing, we
3. Our third question—How are meaningless sensa- tend to see them as remaining the same, a
tions combined into meaningful perceptions?—can
be answered by analyzing our own perceptual experi- phenomenon that is called (a) .
A person walking away does not appear to grow
ences. Our first awareness of some outside stimulus is smaller, even though the image on the retina is decreasing in size,
called a (a) . This awareness results
when some change in energy activates sensory recep- because of (b) constancy. Even though the
image of a door that is opened and closed changes on the retina
tors, which produce signals that, in turn, are trans- from a rectangle to a trapezoid, we see it as retaining its rectan-
formed by the brain into meaningless sensory experiences. When
many individual sensations are assembled into a meaningful gular outline because of (c) constancy. Even Photo Credits: top left, © Arman Zhenikeyev/Alamy; bottom, © Walter Bibikow/Getty Images
though the color and brightness inside a car are altered when
experience, image, or pattern, it is called a (b) . we drive from bright into dim light, we tend to see little change
The latter is not an exact replica of the real world but rather a
copy that has been changed, biased, or distorted by our unique because of (d) and constancy.

set of (c) . Our brain transforms sensations into E. Depth Perception
perceptions instantaneously, automatically, and without our
awareness.
7. The visual system transforms
the two-dimensional image
4. The (a) argued that we can explain how (height and width) of stimuli
perceptions are formed by dividing perceptions into smaller and
smaller elements. They believed that we combine basic elements projected onto the retina into a
three-dimensional experience
to form a perception. In contrast, the (b) by adding depth. Cues for depth
psychologists replied that the formation of perceptions cannot be
understood by simply breaking perceptions down into individual that are dependent on both eyes
are called (a) ; cues for depth that are dependent
components and then studying how we reassemble them. They on only a single eye are called (b) . The binocu-
argued that “the whole is more than the sum of its parts,” by
which they meant that perceptions are more than a combination lar cue for depth that arises when muscles turn your eyes inward
is called (c) . The binocular cue for depth that
of individual elements. The Gestalt psychologists believed that arises because the two eyes send slightly different images to the
the brain has rules for assembling perceptions, which they called
principles of (c) . brain is called (d) .

142 M O D U L E 6 P E R C E P T I O N

8. There are a number of monocular cues for depth. When an I. ESP: Extrasensory Perception
object appears closer because it overlaps another, the cue is called
(a) . When parallel lines seem to stretch to a 13. The perception and transmission of
thoughts or images by other than normal
point at the horizon and create a sense of distance, the cue is sensory channels are referred to as psychic
called (b) . When two figures are expected to be
the same size but one is larger and thus appears closer, the cue is experiences or (a) phenomena.
ESP, which stands for (b) ,
called (c) . If dust or smog makes objects appear includes four psychic abilities. The ability to transfer
hazy and thus farther away, the cue is called (d) .
As texture changes from sharp and detailed to dull and mono- one’s thoughts to another or read another’s thoughts
is called (c) . The ability to foretell
tonous, it creates the impression of distance; this cue is called events is called (d) . The ability to perceive
(e) . The play of light and shadow gives objects a
three-dimensional look, a cue that is called (f) . events or objects that are out of sight is called (e) .
The ability to move objects without touching them is called
As you ride in a car, the impression that near objects are speeding (f) . Two reasons many researchers are skeptical
by and far objects are barely moving is called (g) .
of psychic abilities are that some supposedly psychic phenomena
were actually accomplished with (g) and
F. Illusions some previous studies that supported ESP had questionable
(h) . Although some studies supported the
9. For much of the time, our perceptions are occurrence of psi phenomena, recent studies showed that the
relatively accurate reflections of the world
(except for anything added by our attentional, experiments that supported psi phenomena could not be
(i) .
motivational, or emotional filters). However,
if perceptual cues that we have learned to use
and rely on are greatly changed, the result is a J. Application: Creating Perceptions
distorted image, called an .
Although illusions are extreme examples, they 14. When you view objects moving in
space, it is called (a)
illustrate that perception is an active, ongoing process in which we motion. When you view images of station-
use past experiences to interpret current sensory experiences.
ary objects that are presented in a rapid
sequence, it is called (b)
G. Research Focus: Influencing Perception motion, which is the basic principle used to
create movies. The illusion that stationary
10. Brief auditory or visual messages that are presented below the lights are moving can be traced to the work of Max Wertheimer,
absolute threshold, which means that their chance who called this phenomenon (c) movement.
of being heard or seen is less than 50%, are called A perceptual experience that is created by allowing the viewer
(a) . Researchers have concluded to enter and participate in computer-generated images is called
that any behavioral changes attributed to sublimi- (d) ; it breaks down some of the traditional
nal messages actually result because listeners’ boundaries between reality and fantasy. Virtual reality has been
strong belief that a behavior will change leads them applied to treat excessive fear of spiders, flying, or heights, which
Photo Credit: (#14) Ames Research Center/NASA, photo by Walt Sisler are called (e) .
to act, unknowingly, to change that behavior; this is called a
(b) .

H. Cultural Diversity: Influence on Perceptions Answers: 1. absolute threshold; 2. (a) just noticeable difference, (b) Weber’s;
3. (a) sensation, (b) perception, (c) experiences; 4. (a) structuralists,
11. Experiences that are typical of a society and (b) Gestalt, (c) perceptual organization; 5. (a) figure, (b) ground,
shared by its members are called (c) simplicity, (d) similarity, (e) proximity, (f) continuity, (g) closure;
influences. These influences have significant effects 6. (a) perceptual constancy, (b) size, (c) shape, (d) color, brightness;
on the perception of images, constancy, depth, and 7. (a) binocular, (b) monocular, (c) convergence, (d) retinal disparity;
motion. 8. (a) interposition, (b) linear perspective, (c) relative size, (d) atmospheric
perspective, (e) texture gradient, (f) light and shadow, (g) motion parallax;
12. Because of cultural influences, Americans tend to engage 9. illusion; 10. (a) subliminal messages, (b) self-fulfilling prophecy;
more in (a) thinking, while Easterners 11. cultural; 12. (a) analytical, (b) holistic; 13. (a) psi, (b) extrasensory
(Japanese) engage more in (b) thinking. perception, (c) telepathy, (d) precognition, (e) clairvoyance, (f) psychokine-
sis, (g) trickery, (h) methodology, (i) replicated; 14. (a) real, (b) apparent,
(c) phi, (d) virtual reality, (e) phobias

S U M M A R Y T E S T 143

Critical Thinking

Taste Shapes? Hear Colors? Smell Sounds?

QUESTIONS When Carol Crane hears the that come from sensory organs, such 4 Which part of the
sound of guitars, she feels as if as the eyes and ears, travel to places neuron is respon-
1If researchers someone is blowing on her ankles. in the brain they shouldn’t necessar- sible for taking signals
wanted to better Hearing the piano gives her a tap- ily be going to, which leads to the that come from senso-
understand how ping sensation on her chest. Hearing signals being interpreted as multiple ry organs to multiple
Carol’s brain processes jazz music makes her feel as if heavy, sensations. For example, when peo- areas of the brain?
sensory experiences, sharp raindrops are falling all over ple experience color sensations when
which type(s) of brain her body! When Carol looks at the hearing words, hearing words acti- 5 Which brain areas
scan should they use? number 4, she sees red, and when she vates areas of the brain responsible are responsible
looks at the letter b, she sees blue. for both hearing and vision. for hearing words and
2 Is synesthesia a Carol is unique from most other peo- seeing colors?
type of illusion? ple because of the complex way she Other biological research suggests
experiences many sensations. that synesthesia runs in families; 6 Which modern
3 Does having however, its genetics are not well un- approach to
synesthesia help Carol has an uncommon condi- derstood. Researchers recently made psychology is used
improve your memory? tion called synesthesia, which means a significant stride in understanding to study the genetic
when one of her senses gets stimu- the genetic involvement of synesthe- involvement of
lated, another sense automatically, sia. They identified specific chro- synesthesia?
involuntarily gets stimulated too. mosomal regions associated with
Perceiving colors with letters and auditory-visual synesthesia, which ANSWERS
numbers is the most common form is when people see colors in response TO CRITICAL
of synesthesia. Less common types to sounds. Still, the genetic basis for THINKING
include experiencing sounds with synesthesia is complex and under- QUESTIONS
smells and shapes with f lavors. standing how it develops requires
Sometimes, the associations are rea- much further study. Researchers are
sonable or logical, such as the smell hopeful that understanding the
of lemons leading people to see yel- genetic involvement in synesthesia
low. But, other times, the associa- will also help them better understand
tions are surprising, such as the how the brain is organized and how
smell of lavender leading people to different areas are connected, ulti-
see green and to feel stickiness. mately leading to a better under-
standing of human perception.
Many people with synesthesia (Adapted from Asher et al., 2009;
enjoy their special abilities; however, Callejas, 2008; Cytowic, 1999; Hitti,
there is a real downside for others. 2006b; Hubbard & Ramachandran,
Some people experience unpleasant 2005; Lemley, 1999; Nunn et al.,
associations, such as the awful taste 2002; Rouw & Scholte, 2007; Steven
of earwax when hearing certain et al., 2006; Weir, 2009)
words. As you can imagine, this can
make reading very unpleasant! As a
result of having multiple senses
stimulated, people can experience
distractions at work, while reading
or studying, or while driving and
looking at road signs. These unique
experiences can be frustrating be-
cause they are frequent and auto-
matic, making them very difficult to
prevent or stop.

Researchers have been studying
people with synesthesia and have
learned some fascinating things. In
people with synesthesia, the signals

144 M O D U L E 6 P E R C E P T I O N

Links to Learning

Key Terms/Key People Learning Activities

absolute threshold, 122 perception, 124 PowerStudy for Introduction PowerStudy 4.5™
Ames room, 133 perceptual constancy, 128 to Psychology 4.5
apparent motion, 140 perceptual sets, 137
atmospheric personalized Try out PowerStudy’s SuperModule for Perception! In addition to the quizzes,
learning activities, interactive Summary Test, key terms, module outline and
perspective, 131 perceptions, 125 abstract, and extended list of correlated websites provided for all modules, the
binocular depth cues, 129 phi movement, 140 DVD’s SuperModule for Perception features:
brain: association Ponzo illusion, 133 t 4FMG QBDFE
GVMMZ OBSSBUFE MFBSOJOH XJUI B NVMUJUVEF PG BOJNBUJPOT
precognition, 138 t 7JEFP BCPVU NPUJPO QBSBMMBY
UIF "NFT SPPN
BOE WJSUVBM SFBMJUZ UIFSBQZ
areas, 125 proximity rule, 127 t *OUFSBDUJWF WFSTJPOT PG TUVEZ SFTPVSDFT
JODMVEJOH UIF 4VNNBSZ 5FTU PO
brain: primary areas, 125 psi, 138 pages 142–143 and the critical thinking questions for the article on page 144.
brightness constancy, 128 psychokinesis, 138
clairvoyance, 138 real motion, 140 CengageNOW!
closure rule, 127 relative size, 130 www.cengage.com/login
color constancy, 128 replication, 139 Want to maximize your online study time? Take this easy-
continuity rule, 127 retinal disparity, 129 to-use study system’s diagnostic pre-test and it will create a personalized study
convergence, 129 rules of organization, 127 plan for you. e plan will help you identify the topics you need to understand
cultural influences, 136 self-fulfilling better and direct you to relevant companion online resources that are specific
depth perception, 129 to this book, speeding up your review of the module.
extrasensory prophecies, 135
sensation, 124 Introduction to Psychology Book Companion Website
perception, 138 shape constancy, 128 www.cengage.com/psychology/plotnik
Fechner, Gustav, 122 similarity rule, 127 Visit this book’s companion website for more resources to help you
figure-ground rule, 127 simplicity rule, 127 study, including learning objectives, additional quizzes, flash cards, updated
Ganzfeld procedure, 139 size constancy, 128 links to useful websites, and a pronunciation glossary.
Gestalt psychologists, 126 stimulus, 125
illusion, 132 structuralists, 126 Study Guide and WebTutor
impossible figure, 137 subliminal message, 135 Work through the corresponding module in your Study
interposition, 130 subliminal stimulus, 122 Guide for tips on how to study effectively and for help learning the material
just noticeable telepathy, 138 covered in the book. WebTutor (an online Study Tool accessed through your
texture gradient, 131 eResources account) provides an interactive version of the Study Guide.
difference, 123 threshold, 122
light and shadow, 131 transduction, 125
linear perspective, 130 virtual reality, 141
monocular depth cues, 130 Weber’s law, 123
moon illusion, 132
motion parallax, 131
Müller-Lyer illusion, 133

Suggested Answers to Critical Thinking the axons likely take signals to two areas of the brain, one where it
is supposed to go and another it shouldn’t be sending information
1. The two types of brain scans that measure activity of neurons during to. This process may explain why these people experience multiple
sensory experiences are the fMRI (functional magnetic resonance simultaneous sensations after only one sense is stimulated.
imaging) and PET (positron emission tomography) (pp. 70–71).
5. The temporal lobe is involved with hearing, and the occipital lobe
2. No. An illusion is a perceptual experience in which you perceive an image is involved with vision. More specifically, the auditory association
as being so strangely distorted that, in reality, it cannot and does not exist. area within the temporal lobe transforms basic sensory informa-
Synesthesia involves not only having visual sensations but also experienc- tion, such as sounds, into recognizable auditory information, such
ing two different sensations triggered by the stimulation of one sense. as words (p. 78). Also, the primary visual cortex within the occipi-
tal lobe receives electrical signals and transforms these signals
3. The more associations we make with information we are trying to store into colors (p. 79).
in our memory, the more likely we are to remember it well. People with
synesthesia activate multiple areas of their brain when experiencing 6. The biological approach (p. 6) examines how our genes interact
sensory information. This leads to making more associations with these with our environment to influence many abilities, including the
experiences and likely improves their ability to recall information later. processing of sensory information.

4. The dendrites receive the electrical signals from the sensory organ and L I N K S T O L E A R N I N G 145
later send the information through the axons to reach the specific area of
the brain to experience a particular sensation. In cases of synesthesia,

Sleep

7 & Dreams
MODULE
148
Photo Credit: © Louie Psihoyos/Science150
Faction/Corbis152
A. Continuum of Consciousness 155 Summary Test 164
B. Rhythms of Sleeping & Waking 156 Critical Thinking 166
C. World of Sleep 158
D. Research Focus: Circadian Preference 159 Texting: How Distracting Can It Be? 167
E. Questions about Sleep 160 Links to Learning
Concept Review 162
F. Cultural Diversity: Incidence of SAD PowerStudy 4.5™
G. World of Dreams Complete Module
H. Application: Sleep Problems & Treatments

146

Introduction

Living in a Cave e advertisement read: “We are looking for in great detail and depth and doing so in a reasonably naturalistic
a hardy subject to live alone in an under- setting. Researchers discovered that the preferred length of a day
Would is not 24 hours and that during a particular kind of sleep Stefania’s
eyes moved back and forth as if she were watching a ping-pong
you answer ground cave for four months. We’ll provide game. e significance of these eye movements emphasizes the fact
board, room, and a monthly allowance. It that some major discoveries in science occur quite by accident.
this ad? will be necessary to take daily physiological

measurements, measure brain waves, and collect blood samples.” Chance Discovery
Twenty people answered this ad, but researchers selected
Stefania because she seemed to have the inner strength, motivation, In the early days of sleep research, psycholo-
and stamina to complete the entire four months. On the chosen Why are gists were observing changes in sleeping sub-

day, Stefania crawled 30 feet underground with her favorite books your eyes jects and noticed that during a certain stage
into a 20-by-12-foot Plexiglas module, which had been sealed off of sleep a person’s eyes suddenly began to
from sunlight, radio, television, and other time cues. moving? move rapidly back and forth. is back-and-

During her first month underground, Stefania’s concentration forth eye movement can actually be seen under the eyelids in the
seemed to come and go. She appeared depressed, and she snapped photos below. Even more interesting, when subjects were awakened
at researchers when they asked her to do routine measurements.
She had strange dreams—for example, that her computer monitor
had turned into a TV that was talking to her. A er several months,
however, she became more comfortable with her underground iso-
lation. She followed a regular routine of taking her body tempera-
ture, heart rate, and blood pressure and typing the results into a
computer monitor, her only link with the outside world.
Without clocks, radio, television, or the sun, Stefania found it
difficult to keep track of time, which seemed to have slowed down.
When told she could leave her underground cave (photo below)
because her 130 days were up, she felt certain she had been under-
ground only about 60 days. Her time underground, which was a
women’s record (the men’s record is 210 days), allowed researchers
to closely monitor her sleeping and waking behaviors in the absence
of all light and time cues (adapted from Newsweek, June 5, 1989).

Photo Credits: left, © Murrae Haynes; right, © Stockbyte/Getty Images Stefania leaves an underground cave in which she had lived for 130 days During one kind of sleep (REM—rapid eye movement sleep),
without any time cues (clocks, sunshine, radio, TV). the eyes dart back and forth beneath the eye lids.

Asking Stefania to live in a cave for many months was not a pub- during rapid eye movement, they usually reported that they had
licity stunt but a way to answer questions about how long a day is been dreaming. is chance observation of rapid eye movement
and how much one sleeps when there are no light cues. To answer and its high association, or correlation, with dreaming gave
these questions, researchers used a case study approach, which researchers a reliable method to identify and study dreaming in
meant studying Stefania’s behaviors and physiological responses the laboratory (Dement & Kleitman, 1957).

ese examples show how researchers study waking, sleeping,
and dreaming in different settings, including underground caves
and sleep laboratories, and also how they were helped along by a
chance discovery.

What’s Coming

We’ll discuss the preferred length of a day, how you know when to
sleep and wake up, what happens to your body and brain during
sleep, how much sleep you need, why you sleep, and common sleep
problems and their treatments. We’ll also discuss the one question
students always ask: What do dreams mean? All these areas fit
neatly under a much broader phenomenon that we call awareness,
or consciousness, and that is where we’ll begin.

I N T R O D U C T I O N 147

A. Continuum of Consciousness

Different States

Are you One curious and amazing feature of con- One way you know that you are conscious is that you are aware of
sciousness is that, at some point, the person is your own thoughts and existence (Pinker, 2000). You may think that
conscious actually observing himself or herself (Rochat, when awake you are conscious and when asleep you are unconscious,
2003). For example, how do you know that at but there is actually a continuum of consciousness.
now? this very moment you are conscious?
The continuum of consciousness refers to a wide range of experiences,
Consciousness refers to different levels of awareness of one’s thoughts from being acutely aware and alert to being totally unaware and unresponsive.

and feelings. It may include creating images in one’s mind, following We’ll summarize some of the experiences that make up the
continuum of consciousness.
one’s thought processes, or having unique emotional experiences.

Controlled Processes Automatic Processes Daydreaming Altered States
Many of us engage in a plea-
A problem with cell phones is we surable form of conscious- Over 3,000 years ago, Photo Credits: left, © Michael S. Yamashita/Corbis; center left, © PhotosIndia/Getty Images; center right, © Image Source/Jupiterimages; right, © David Harry Stewart
have the ability to focus all of our ness called daydreaming. Egyptians brewed alcohol to
attention on only one thing, which is reach altered states of con-
an example of controlled processes. Daydreaming is an activity sciousness (Samuel, 1996).
that requires a low level of Altered states of conscious-
Controlled processes are activities awareness, often occurs dur-
that require full awareness, alertness, ing automatic processes, and ness result from using any num-
and concentration to reach some goal. involves fantasizing or dream-
The focused attention required in carry- ing while awake. ber of procedures—such as
ing out controlled processes usually
interferes with the execution of other We may begin day- meditation, psychoactive drugs,
ongoing activities. dreaming in a relatively
Eating while reading is conscious state and then hypnosis, or sleep deprivation—to
Talking on a cell phone while an automatic process. dri into a state between
driving is a controlled process. sleep and wakefulness. produce an awareness that differs
Since this man’s attention Usually we daydream in
A controlled process such as talk- is focused primarily on situations that require little from normal consciousness.
ing on a cell phone while driving reading an important attention or during repeti-
involves focusing most of your atten- report, he is almost auto- tious or boring activities. For example,
tion on talking and little on driving. matically eating the apple; this woman is using
this is an example of an Men’s and women’s meditation to focus
ere’s less problem if the driving automatic process. daydreams are similar. her attention on a
is easy, but if you need to take quick single image or
action, your driving will likely suffer Automatic processes Most daydreams are thought,
because your attention is primarily are activities that require lit- rather ordinary, such as free her
focused on your phone conversation tle awareness, take minimal thinking about getting one’s mind from
(P. J. Cooper et al., 2003). In fact, attention, and do not inter- hair cut, planning where external
listening to a conversation while fere with other ongoing to eat, or fantasizing about restraints,
driving increases brain activity in activities. a date. ese kinds of day- and enter an Meditation is an
language areas and decreases brain dreams serve to remind us altered state altered state.
activity in spatial areas involved Examples of automatic of important things in our
in driving (Just, 2008). People who processes include eating future. Although you might of consciousness.
use cell phones while driving have while reading or watch- guess otherwise, men’s In an interesting series of
4 times the risk of having an acci- ing television and driving and women’s daydreams studies on himself, neuro-
dent (Kirtland, 2009). e use of a car along a familiar are remarkably similar in psychologist John Lilly (1972)
a cell phone is the most common route while listening to frequency, vividness, and repeatedly took LSD (when it
distraction while driving (NHTSA, the radio or thinking of realism (Klinger, 1987). was legal) and reported that it
2008). For these reasons, handheld something else. caused unusual, bizarre, and
cell phones are banned in six states sometimes frightening altered
(O’Donnell, 2009). Although we seem to states of consciousness. For
concentrate less during example, he described leaving
automatic processes, at his body, seeing it from above,
some level we are con- and being afraid he would not
scious of what is occur- be able to return safely to it.
ring. For instance, as we e chief characteristic
drive on automatic pilot, of altered states, whichever
we avoid neighboring way they are produced, is that
cars and can usually take we perceive our internal and
quick evasive action external environments or
during emergencies. worlds in ways different from
normal perception.

148 M O D U L E 7 S L E E P & D R E A M S

Sleep and Dreams Unconscious and Implicit Memory Unconsciousness
We enter an altered state of We told you that one of Sigmund Freud’s
consciousness every night revolutionary ideas was his concept of the If you have ever fainted,
when we go to sleep. unconscious (see pp. 9, 434–437). gotten general anesthesia,
or been knocked out from a
Sleep consists of five differ- According to Freud’s theory, when we are blow to the head, you have
ent stages that involve different faced with very threatening wishes or desires, experienced being uncon-
levels of awareness, con- especially if they are sexual or aggressive, we scious or unconsciousness.
sciousness, and responsive- automatically defend our self-esteem by plac- Unconsciousness, which
ness, as well as different levels ing these psychologically threatening thoughts
of physiological arousal. The into a mental place of which we are not aware, can result from disease, trauma,
deepest state of sleep borders called the unconscious. We cannot voluntarily
on unconsciousness. recall unconscious thoughts or images. a blow to the head, or general

Because of our decreased Freud believed that we can become medical anesthesia, results in Unconsciousness results
awareness, 8 hours of sleep aware of our unconscious thoughts only total lack of sensory awareness from a head knock,
may seem like one con- through a process of free association or and complete loss of respon- disease, or general
tinuous state. However, it is dream interpretation, siveness to one’s environment. anesthesia.
actually composed of dif- both of which are
ferent states of body arousal explained on For example, a boxer’s goal is to knock out the
and consciousness (Lee- page 435. opponent with a quick blow to the head that produces
Chiong, 2008). One inter- a temporary state of unconsciousness. Being in an acci-
esting sleep state involves Freud’s idea of the unconscious is dent can damage the brain and cause different levels of
dreaming. different from implicit memory. unconsciousness and result in different kinds of comas.
In some comas, a person appears to be asleep and has
Dreaming is a unique state Somewhat related to Freud’s theory absolutely no awareness or responsiveness; this is called
of consciousness in which we of the unconscious is a new concept a vegetative state. People in vegetative comas are uncon-
are asleep but experience a developed by cognitive neuroscientists scious and in some cases brain-dead, which means they
variety of astonishing visual, called implicit or nondeclarative memory will never again regain consciousness.
auditory, and tactile images, (Frensch & Runger, 2003).
often connected in strange Several Kinds Consciousness is so mysterious
ways and often in color. People Implicit or nondeclarative memory because it is a continuum of
blind from birth have only audi- means learning without awareness, such as Why is it
tory or tactile dreams. occurs in emotional situations or in acquiring
habits. We are unaware of such learning, so mysterious? states, which range from the
Newborns sleep about which can influence our conscious feelings, tragic unconsciousness of being
Photo Credits: left, © Haig Kouyoumdjian; center, © Cesar Paredes; right, © Tim Shaffer/Reuters/Corbis 17 hours a day. thoughts, and behaviors. in a vegetative coma to the keen alertness of controlled
processes during a final exam. Although it is difficult to
During the initial stage For example, you cannot describe the define consciousness, you know what it feels like to be
of sleep, we are o en aware complex motor movements your feet make conscious and aware of your thoughts and surround-
of stimuli in our environ- as they walk down stairs because such ings. Neuroscientists find there is no single seat of con-
ment. However, as we pass motor memories are stored in implicit sciousness; rather it results from interactions among
into the deepest stage of memory, which you are unaware of and many different areas of the brain, depending upon the
sleep, we may sleeptalk or cannot voluntarily recall. Implicit memory kinds of thoughts, images, or stimuli to which you are
sleepwalk and children explains why people cannot recall and attending (Edelman, 2003).
may experience frightening are unaware of why or how they learned Although you have experienced having conscious
night terrors but have no to fear a tiny spider, fell in love, fainted at beliefs and desires, Freud believed that there was also an
awareness or memory the sight of blood, or learned (classically active, unconscious psychological process that defended
of them. conditioned) to make a happy or sad facial you against threatening sexual and aggressive thoughts,
expression (Poldrack & Packard, 2003). of which you are totally unaware. In partial support of
Most of this module Implicit memory emphasizes the learning Freud’s theory, cognitive neuroscientists use the con-
focuses on waking, sleeping, and influence of many different kinds of cept of implicit or nondeclarative memory to explain
and dreaming. motor and emotional memories and is how you can be unaware of perceiving various stimuli,
different from Freud’s unconscious, which such as words, objects, faces, and emotional events,
focuses on the influence of threatening and even learn simple responses (classical condition-
memories (Kihlstrom, 1993). ing). Although you are not aware of this unconscious
learning, you can be unknowingly influenced by the
thoughts, memories, feelings, and behaviors stored in
your implicit memory (Guterl, 2002; Petty et al., 2006).
One obvious sign of consciousness is being awake,
which is regulated by a clock in the brain, our next topic.

A . C O N T I N U U M O F C O N S C I O U S N E S S 149

B. Rhythms of Sleeping & Waking

Biological Clocks

Sleep researchers studied Stefania (left photo), clock, radio, television) from cave dwellers like Stefania, the circa-
How long who is shown coming out of her modernized cave dian clock day was believed to lengthen from 24 hours to about 25
is a day? a er 130 days. Stefania was asked to live in a cave hours (M. W. Young, 2000). However, in a better controlled study,
so researchers could study her biological clocks. researchers reported that for both young (mean age 24) and older
Biological clocks are internal timing (mean age 67) adults, the sleep-wake circadian clock is genetically
devices that are genetically set to regulate set for a day lasting an average of 24 hours and 18 minutes (Czeisler
various physiological responses for differ- et al., 1999).
ent periods of time. Resetting the circadian clock. Because your circadian clock

Biological clocks can be set for is genetically set for about 24 hours, 18 minutes, it must be reset
hours (secretion of urine), for a each day to match our agreed upon 24-hour-long day. e resetting
single day (rise and fall in internal stimulus is morning sunlight, which stimulates newly discovered
Stefania’s sleep-wake cycle body temperature), or for many days light-detecting cells in the eye’s retina (see p. 96) (Purves et al.,
in the cave was regulated by (women’s 28-day menstrual cycle). 2008). ese retinal cells, which are involved in sensing the amount
We are interested in a biological clock of light and are not involved in seeing, send electrical signals to the
a biological clock.

that is set for a single day and produces what Length of Day brain’s circadian clock (described below)
is called a circadian (sir-KAY-dee-un) rhythm 24 hr, 18 min 24 hr and reset it by about 18 minutes each day
(circa means “about”; diem means “day”). Body’s circadian clock Industrial world’s clock (Purves et al., 2008).

A circadian rhythm refers to a biological clock Problems. If your circadian clock is

that is genetically programmed to regulate physio- not properly reset each day, it may result

logical responses within a time period of 24 hours in problems getting to sleep, getting over

(about one day). jet lag, and adjusting to working the night

Length of day. You are most familiar shift (see next page). Although the circa-
with the circadian rhythm that regulates your sleep-wake cycle. dian clock was long known to exist, only recently have researchers
In previous studies, when researchers removed all time cues (light, identified its exact location in the brain.

Location of Biological Clocks
It may seem strange to think of having clocks Besides the 24-hour sleep-wake circadian clock, you also have
Where is in your brain. Actually you have several other clocks in your brain, including one that measures Photo Credits: top left, © Murrae Haynes; bottom right, © Burger/Phanie/Photo Researchers, Inc.
the circadian clocks, including the biological circadian shorter periods of time, called an interval timing
sleep-wake clock located in a group of cells clock (Buhusi & Meck, 2005).
clock?
in the brain’s suprachiasmatic (SUE-pra- The interval timing clock, which can be started
Suprachiasmatic kye-as-MAT-ick) nucleus (Lee-Chiong, and stopped like a stopwatch, gauges the passage of
nucleus 2008; Wallisch, 2008). seconds, minutes, or hours and helps people and ani-
The suprachiasmatic nucleus is one of mals time their movements, such as knowing when to
many groups of cells that make start or stop doing some activity (taking a one-hour nap
and actually waking up about an hour later). The interval timing clock is
up the hypothalamus, located in a part of the brain known as the basal ganglia (see p. 60).

which lies in the lower Another clock in your brain is regulated by food.
The food-entrainable circadian clock
Optic nerve middle of the brain. The (also referred to as the midnight-snack clock)
suprachiasmatic nucle- regulates eating patterns in people and animals
and might be responsible for late-night eating
The sleep-wake circadian us is a sophisticated bio- in people. Thus, obese people, many of whom
clock is located in the logical clock that regulates a eat more than half their calories at night, may
number of circadian rhythms, have an abnormality in their clock, which is
suprachiasmatic nucleus. including the sleep-wake cycle. Because located in the hypothalamus (see p. 80) (C.
Brownlee, 2006b; Mieda et al., 2006).
this nucleus receives direct input from the eyes, the suprachiasmatic cells Walking around with several fine-
tuned biological clocks in your head is
are highly responsive to changes in light. great for timing activities. However, if
your circadian sleep-wake clock is inter-
Since light regulates sleep-wake circadian rhythms, the absence fered with or not properly reset, you may
of light should disrupt circadian rhythms in blind people and have various sleep-wake problems.
cause sleep problems. Researchers found that many blind people do
report sleep problems (Lamberg, 2006; Moreno, 2006). However,
some people who are completely blind report no sleep problems
because the pathway for transmitting light from their eyes directly
to the suprachiasmatic nucleus, which is not involved in seeing, is
intact (Barinaga, 2002; Foster, 2009).

150 M O D U L E 7 S L E E P & D R E A M S

Circadian Problems and Treatments

What if your Here’s the basic problem: For most of morning sunlight, which our eyes send directly to the supra-
the industrial world, a day is agreed to chiasmatic nucleus. is daily resetting of our sleep-wake clocks
circadian clock be exactly 24 hours long, but for your about 18 minutes usually occurs automatically. However, if our
is upset? genetically set sleep-wake circadian circadian clocks are not properly reset, we may experience
decreased cognitive performance, work-related and traffic acci-
clock, a day is an average of 24 hours dents, jet lag, and various sleep disorders (Aamodt & Wang, 2008;
and 18 minutes. This difference means your sleep-wake clock K. Wright, 2002).
must be reset about 18 minutes each day. e resetting stimulus is

Shift Workers Jet Lag Resetting Clock Melatonin

Photo Credit: left, © Philip Rostron/Masterfile Staying awake when your If you flew from west coast to Researcher Charles Czeisler e discovery of a use for mela-
sleep-wake clock calls for east coast, you experienced a (1994) spent ten years convincing tonin has been a big scientific
sleep results in decreased 3-hour time difference and his colleagues that light could breakthrough (Kra , 2007).
performance in cognitive most likely had jet lag. reset circadian clocks. A er
and motor skills (Drum- he finally succeeded, other Melatonin is a hormone that
mond, 2000). For example, Jet lag is the experience of researchers used his and their is secreted by the pineal gland,
employees who work the fatigue, lack of concentration, and own research to obtain patents an oval-shaped group of cells
graveyard shi (about 1–8 reduced cognitive skills that for light therapy (Nowak, 1994). that is located in the center of the
..) experience the high- occurs when travelers’ biological human brain. Melatonin secretion
est number of accidents, circadian clocks are out of step or Light therapy is the use of bright increases with darkness and
reaching their lowest synchrony with the external clock artificial light to reset circadian decreases with light. The supra-
point, or “dead zone,” at times at their new locations. clocks and to combat the insomnia chiasmatic nucleus regulates the
about 5 .., when it is secretion of melatonin, which plays
very difficult to stay alert Generally, it takes about and drowsiness a role in the regulation of circadian
(Stutts et al., 2002). one day to reset your circa- that plague rhythms and in promoting sleep.
dian clock for each hour of shift workers
e reason shi work- time change. and jet-lag Suprachiasmatic
ers and late-night drivers sufferers. nucleus
have more accidents is Jet lag occurs when a It also helps
their sleep-wake clocks body’s circadian clock gets people with Pineal gland Optic nerve
have prepared their bodies sleeping disor-
for sleep, which means out of synchrony. Melatonin is a hormone
they feel sleepy, are less ders in which secreted by pineal gland.
attentive and alert, and Consider how severe jet lag the body fails to stay in time with
are o en in a lousy mood can be for flight attendants the external environment. Although early testimonials
(Ohayon et al., 2002). who frequently make long and studies claimed melatonin
Frequent major changes in trips. ose who do not take For example, researchers reduced jet lag, a later double-
working hours will likely breaks to allow their circadian report that workers who had blind study reported that
cause much stress on the clocks to readjust experience been exposed to bright light melatonin was no better than
body and brain (Aamodt impaired cognitive skills and then shi ed to night work a placebo in reducing jet lag
& Wang, 2008). (Aamodt & Wang, 2008). showed improvement in alert- (Spitzer et al., 1999). However,
ness, performance, and job melatonin helped individuals
Next, we’ll see how cir- A er 3 months in space, satisfaction (Czeisler et al., 1995). with medical problems result-
cadian rhythms can also astronauts experience “space Exposure to bright light (about ing from chronically disrupted
create problems for long- lag” or sleeplessness because 20 times brighter) at certain circadian clocks sleep better
distance travelers, includ- their circadian clocks are not times reset the workers’ suprachi- and experience less fatigue
ing flight attendants who being reset (Monk et al., 2001). asmatic nucleus and resulted in a (Nagtegaal et al., 2000).
frequently travel across closer match between their inter-
many time zones. Next, you’ll see how nal circadian clocks and their A new experimental drug
researchers are studying ways external shi ed clock times. has shown initial promise in
to more effectively reset our resetting the circadian clock,
biological clocks. Light therapy has enormous which may bring relief to shi
potential for resetting our sleep- workers and jet-lag sufferers
wake clocks, and more recently (Rajaratnam et al., 2009).
it has been used to treat depres-
sion (B. Bower, 2005; Tompkins, Next, we’ll examine what
2003a, 2003b). happens inside the brain and
body during sleep.
Another factor involved in
setting the sleep-wake clock is a
hormone from a gland that was
once thought useless.

B . R H Y T H M S O F S L E E P I N G & W A K I N G 151

C. World of Sleep

Stages of Sleep

Does my e first thing to know about sleep is are recorded by a complex machine
that your brain never totally sleeps but called an EEG, or electroencephalo-
brain sleep? is active throughout the night. To track Amplitude: gram. Each stage of sleep can be rec-
your brain’s activity during sleep, Height of waves ognized by its distinctive pattern of
researchers would attach dozens of tiny wires or electrodes EEGs, which we’ll explain here.
to your scalp and body and record electrical brain activity as
you passed through the stages of sleep. Alpha Stage

The stages of sleep refer Before actually going into the first

to distinctive changes in the Frequency: Number of stage of sleep, you briefly pass through
cycles (waves) per second a relaxed and drowsy state, marked by
electrical activity of the brain

and accompanying physio- characteristic alpha waves.

logical responses of the body that The alpha stage is marked by feelings of

occur as you pass through different being relaxed and drowsy, usually with the

phases of sleep. eyes closed. Alpha waves have low amplitude

As shown in the graph at the and high frequency (8–12 cycles per second). Alpha waves
top, brain waves are described
Going to sleep involves going in terms of frequency (speed) A er spending a brief time relaxing (8–12 cycles per second)
through several different stages. and amplitude (height). They in the alpha stage, you enter stage 1 of
non-REM sleep.

Non-REM Sleep e second thing to know about sleep is that it is stages 1, 2, 3, and 4; each stage is identified by a particular pattern
divided into two major categories, called non- of brain waves and physiological responses. (REM stands for rapid
What REM and REM. We’ll discuss non-REM first. eye movement.)
happens
during sleep? Non-REM sleep is where you spend approximately You begin in sleep stage 1 and gradually enter stages 2, 3,
80% of your sleep time. Non-REM is divided into sleep and 4 (Rama et al., 2006).

Stage 1 Stage 2 Stages 3 and 4

is is the lightest stage of sleep. This is the first stage of what About 30–45 minutes after drifting off into sleep, you pass
Stage 1 sleep is a researchers call real sleep. through stage 3 and then enter into stage 4 sleep.
Stage 4 sleep, which is also called slow-wave or
transition from wakeful- Stage 2 sleep
ness to sleep and lasts marks the beginning delta sleep, is characterized by waves of very high
1–7 minutes. In it, you of what we know as
gradually lose responsive- sleep, since subjects amplitude and very low frequency (less than 4 cycles
ness to stimuli and experience drift- who are awakened in
ing thoughts and images. Stage 1 is stage 2 report having per second) called delta waves. Stage 4 is often con-
marked by the presence of theta been asleep. EEG tracings show
waves, which are lower in amplitude high-frequency bursts of brain sidered the deepest stage of sleep because it is the
and lower in frequency (4–7 cycles activity called sleep spindles.
per second) than alpha waves. most difficult from which to be awakened. During
Stage 2
Stage 1 stage 4, heart rate, respiration, temperature, and blood
Sleep
Theta waves spindles flow to the brain are reduced, and there is a marked
(4–7 cycles per second)
As you pass through stage 2, secretion of GH (growth hormone), which controls
Although stage 1 is usually your muscle tension, heart rate,
labeled a sleep stage, some indi- respiration, and body tempera- levels of metabolism, physical growth, and brain development.
viduals who are aroused from it ture gradually decrease, and it
feel as if they have been awake. becomes more difficult for you As you pass through stages 3 and 4, your muscle tension,
to be awakened. heart rate, respiration, and tem-
Next, you enter stage 2 sleep. perature decrease still further, Stage 4

and it becomes very difficult for
you to be awakened.
A er spending a few minutes
to an hour in stage 4, you will
backtrack through stages 3 and
2 and then pass into a new stage,
called REM sleep, which is asso- Delta waves
ciated with dreaming. (less than 4 cycles

per second)

152 M O D U L E 7 S L E E P & D R E A M S

REM Sleep We have discussed one major category of look very similar to beta waves, which occur when you are wide awake

When do sleep, non-REM, and now move on to the and alert. During REM sleep, your body is physiologically very aroused, but

you dream? second major category of sleep, which goes all your voluntary muscles are paralyzed. REM sleep is highly associated
by the initials REM. with dreaming.

REM sleep makes up the remaining 20% of your REM Sleep You pass into REM sleep about five or six times
sleep time. It is pronounced “rem” and stands for throughout the night with about 30 to 90 minutes

rapid eye movement sleep because your eyes move between periods. You remain in each period of REM

rapidly back and forth behind closed lids. REM brain (14–25 cycles per second) sleep for 15 to 45 minutes and then pass back into
waves have high frequency and low amplitude and non-REM sleep.

Characteristics of REM Sleep REM—Dreaming and Remembering

When REM sleep was first discovered in the early 1950s, researchers Dreaming. One of the biggest breakthroughs in dream
found it difficult to believe their unusual findings: Although you are research was the finding that about 80–90% of the times
asleep during REM, your body and brain are in a general state of physi- when subjects are awakened from a REM period, they
ological arousal (Aserinsky & Kleitman, report having vivid, complex, and relatively long dreams
1953). For example, during REM sleep, your (Dement, 1999). In contrast, only
heart rate and blood pressure are signifi- about 10% of subjects awakened
cantly higher than during non-REM sleep from non-REM sleep report simi-
(L. Rosenthal, 2006). Because of this strange lar kinds of dreams.
combination of being asleep yet physiologi- One of the first questions
cally aroused, REM sleep is often called asked was what happens when
paradoxical sleep. (A paradox is something people are deprived of REM sleep
with contradictory qualities.) and dreaming. Many subjects
Another unusual feature of REM sleep is have been deprived of REM sleep Dreaming usually occurs
Eyes dart back and forth that its brain waves are very similar to those and dreaming without show- during REM sleep.
as a sign of REM sleep. recorded when a person is wide awake and
ing any major behavioral or physiological effects (Bonnet,
alert. By looking at brain wave recordings alone, researchers cannot tell 2005). However, suppressing REM sleep does produce a
whether a person is in REM sleep or wide awake. Only the additional curious phenomenon called REM rebound.
recording of rapid eye movements indicates the occurrence of REM sleep. REM rebound refers to individuals spending an increased

Although many physiological responses are greatly increased, you percentage of time in REM sleep if they were deprived of REM

completely lose the muscle tension in your neck and limbs so you are sleep on the previous nights.

essentially paralyzed. However, involuntary muscles that regulate heart, Remembering. e occurrence of REM rebound sug-
lungs, and other organs continue to function. Researchers think humans gests a need for REM sleep, and one such need involves
Photo Credits: top, © Stockbyte/Getty Images; bottom, © Digital Vision Ltd./SuperStock evolved muscle paralysis of their limbs during REM sleep so they would memory. In one study, subjects learned to press a button
not act out violent dreams by running, fighting, or jumping about and when they spotted a moving target on a screen. Subjects
injuring themselves (Schenck, 2003). In fact, this actually happens in tested on the same day as training showed a modest
REM behavior disorder. improvement. However, when subjects were tested the
In REM behavior disorder, which usually occurs in older people, vol- next day, those subjects allowed to get the most REM sleep
untary muscles are not paralyzed, and sleepers can and do act out their
(slept 8 hours) showed the greatest improvement com-
dreams, such as fighting off attackers in dreams. People with this condi- pared to subjects who got the least REM (slept 6 hours).
tion have been known to break a hand, punch a wall, or hurt a spouse Researchers concluded that REM sleep helps us store or
(Seppa, 2009). In some cases, REM behavior disorder is caused by encode information in memory and advise students to get
known neurological damage, but in other cases, the causes are unknown a good night’s sleep so that what they studied the previ-
(Tippmann-Peikert et al., 2006). ous day has a chance to be stored in the brain’s memory
So not only is REM a paradoxical sleep but it also signals dreaming. (Stickgold, 2000, 2005).

Awake and Alert

A short time after awakening from sleep, How alert you feel in the morning partly depends on whether
you enter a state of being awake and alert. you are a morning or an evening person, which we’ll discuss in the
This state has distinctive brain activity Research Focus on page 155.
called beta waves (right figure), Although you now have an overview of
which are characterized by high fre- Awake and Alert the different sleep stages, you may be sur-

quency and low amplitude and are Beta waves prised to discover that how you go through
very similar to those waves observed (14–25 cycles per second) the different stages is somewhat like riding a
during REM sleep. roller coaster.

C . W O R L D O F S L E E P 153

C. World of Sleep

Sequence of Stages A night’s sleep is like a wide blue line and REM sleep is indicated by
roller-coaster ride through red inserts. e numbers 1 to 4 refer to sleep
When you go to sleep at night, different stages of sleep. stages 1, 2, 3, and 4 of non-REM sleep, which
Why is sleep you may think that you simply we discussed earlier.
like a roller- sleep for 8 hours, perhaps toss
coaster ride? and turn a little, and even do Researchers have studied and plotted
changes in brain waves, physiological arousal,
some dreaming. But sleep is not and dreaming as subjects progressed through
one unbroken state; rather, it is a series of recurring the stages of sleep (L. Rosenthal, 2006). Here’s
stages, similar to the ups and downs of a roller-coaster what George will experience on a typical
ride. We’ll describe a typical night’s pattern for George, roller-coaster-like ride through the different
a college sophomore, who goes to bed about 11 .. and stages of a night’s sleep.
gets up about 7 .. As we take you through the figure
below, notice that non-REM sleep is indicated by the

11:00 12:00 1:00 2:00 3:00 4:00 5:00 6:00
REM REM 1
REM REM REM
1

2

22 22 2 2 2

33 33 3 REM
Like George, we may go in
Here’s 4 4 Stage 4 and out of REM sleep five
what happens It is during stage 4 that George or six times, with REM
during a normal Stage 2 may sleepwalk, sleeptalk, or periods becoming longer
night’s sleep. A er George reaches perform other activities, such as toward morning. If
non-REM stage 2, he partially awakening to turn off George wants to remem-
Stage 1 does not awaken but the alarm, pull up the covers, or ber his dreams, he should
As George becomes drowsy, he rather enters REM get up and go to the bathroom. try when he first wakes
will enter non-REM stage 1, sleep. He will remain in However, George will remember up, since his last REM
which is the transition between REM for 15–45 minutes nothing of what happens in period may have occurred
being awake and asleep. and, if awakened, will non-REM stage 4, such as sleep- only minutes before.
likely report dreaming. talking with his roommate or
As sleep progresses, he will When in REM, his walking to the kitchen and get- Research findings indi-
continue to the next stage, body is in a high state ting a snack. He will remain in cate that getting as many
non-REM stage 2, which is the of physiological arousal, stage 4 for a period of time REM periods as possible
first stage of real sleep. During but his voluntary limb before again backtracking to is important in helping
stage 2, he may experience muscles are essentially non-REM stages 3 and 2, and the brain store material
short, fragmented thoughts, so paralyzed. If George then to his second REM period learned the previous day
that if he is awakened, he may experiences nightmares of the night. (Stickgold, 2000).
think he was dreaming. during REM, he will
not act them out or Children sometimes wake up If George has a difficult
He will continue through injure himself because terrified during non-REM stage time awakening from
non-REM stage 3 and finally he cannot move. 4. ese experiences are called sleep, it may be because he
reach non-REM stage 4. When night terrors (see p. 163), but the was in stage 4, the hardest
George enters non-REM stage A er the REM peri- children will have no memory stage to awaken from.
4, which is slow-wave, or delta, od, he goes back down of them the next day. Also, bed-
sleep, he will be very difficult through non-REM wetting, a condition in which Like George, we all
to waken. A er staying in stage stages 2, 3, and 4. children are unable to control go through the sleep
4 for some minutes to an hour, urination while asleep, occurs stages in about the same
he will backtrack to stages 3 during non-REM stage 4. sequence. However,
and then 2. there’s a reason that some
of us hate mornings more
than others.

154 M O D U L E 7 S L E E P & D R E A M S

D. Research Focus: Circadian Preference

Are You a Morning or Evening Person?

Are you an Some students are early birds and seem to Morning persons (score above 74) prefer to get up earlier, go to bed

like morning classes, while night owls hate earlier, and engage in morning activities. Evening persons (score below
early bird or t hem. Resea rchers stud ied d if ferences 45) prefer to get up later, go to bed later, and engage in afternoon-evening
a night owl? between early birds and night owls by devel- activities. Those individuals who scored between 45 and 74 did not express
oping and using a questionnaire. a strong morning or evening preference (J. P. Guthrie et al., 1995).

A questionnaire is a method for obtaining information Score on Morning/Evening Researchers found that there was a morn-
by asking subjects to read a list of written questions and Questionnaire ing/evening continuum with strong preferences
on either end and mixed or
check off or rate their preferences for specific answers. Morning
person
e morning/evening ques- 45 no preferences in the middle
tionnaire asked subjects to rate (Andershed, 2005). One reason a
their preferred times for going Evening 74 person may have a strong morn-
to bed, getting up, and engag- person ing or evening preference is that

ing in physical and mental an inherited genetic circadian
activities, as well as their feelings of alertness in rhythm regulates body temperature, which, in
Morning the morning and evening. e graph here shows turn, affects going to sleep at night and getting Evening
person the results from this questionnaire. up in the morning. person

Body Temperature Differences Brain Differences

One of your body’s circadian rhythms is the sleep-wake cycle, which is regulated Suprachiasmatic Researchers examined
by the suprachiasmatic nucleus in the hypothalamus. Another circadian rhythm nucleus the brains of morning
thought to be regulated by the suprachiasmatic nucleus involves body tempera- and evening people
ture, which falls as we go to sleep and rises a er we get up (Ropper & Samuels, by taking scans of
2009). their brains 10.5
Getting up. Our body temperature is low in the morning and rises through- Pineal gland Optic nerve hours a er wak-

out the day, when we are most active. The temperature of a morning person ing. Compared
rises more quickly, so this person gets up earlier than an evening person. In to morning people, evening people demonstrated
fact, body temperature in a morning person may rise 1–3 hours earlier than the increased activity in the suprachiasmatic nucleus,
temperature in an evening person (Duffy, 2002; Tankova et al., 1994). an area that regulates the sleep-wake cycle. is sug-
Going to bed. e body temperature of a morning person peaks earlier in the gests that evening people are not as susceptible to
evening, so this person goes to bed earlier than an evening person. An evening fatigue, which gives them the advantage in stamina.
person’s body temperature peaks 1–3 hours later, so this person goes to bed later. ese results indicate that the preference for morn-
e suprachiasmatic nucleus regulates the rise and fall of body temperature, which ing or evening may, at least in part, be explained by
Photo Credits: left, © Digital Vision Ltd./SuperStock; right, © John Foxx/Getty Images in turn determines whether you are a confirmed morning or evening person. differences in the activity of the suprachiasmatic
In addition, there are nucleus (C. Schmidt et al., 2009).
brain differences between 94 96 8 100 2 4 6
–––– Given the brain differences between morning
––––
––––
––––

––––
––––
––––

morning and evening Changes in body temperature influence sleep preferences. and evening people, it is no surprise that there are
people. behavioral and cognitive differences as well.

Behavioral and Cognitive Differences

Researchers found that students who were morning people reported When looking at personality differences, researchers found that
being more alert at 8 .., took more morning classes, performed morning people tend to be conscientious introverts while evening
better in morning classes, and studied more in the morning than people tend to be impulsive extroverts (K. Gilbert, 2006).
did students who were evening people (Duffy, 2002; J. P. Guthrie et Finally, there are no differences between sexes in their prefer-
al., 1995). Students who were evening ences for being a morning or evening person. But, over
people but began classes in the morning the course of normal aging, people tend to become
had more attention problems and poorer physiologically and behaviorally more like morning
performance and complained of daytime persons a er age 50, which explains why grandparents
sleepiness (Giannotti et al., 2002). e best are usually early to bed and early to rise (Duffy, 2002).
time for creative thinking, such as brain- Although people differ in being morning or eve-
storming, is the early morning hours for ning persons, they do share similar brain structures
morning people and the late evening Adjust class schedule to your involved in putting them to sleep and waking them up,
hours for evening people (Time, 2006). preference for morning or evening. our next topic.

D . R E S E A R C H F O C U S : C I R C A D I A N P R E F E R E N C E 155

E. Questions about Sleep

Most adults By the time you are 25 years old, you have fallen asleep over 9,000 times and have
need 7–8 spent about 72,000 hours asleep. ere are usually four questions that students ask
hours of about sleep: How much sleep do I need? Why do I sleep? What happens if I go
sleep. without sleep? What causes sleep? We’ll discuss each of these questions in turn.

How Much Sleep Do I Need?
According to a national survey, 16% of adults sleep less than 6 hours a night, 24% sleep 6–6.9 hours, 31% sleep 7–7.9 hours,
What’s the and 26% sleep 8 or more hours (NSF, 2005). Overall, adults in America sleep an average of about 8 hours a night (NSF,

best amount 2008; Robinson & Martin, 2007). If we took a survey of babies, the time spent sleeping would be dramatically different,
as shown in the pie charts below. Beginning at birth and continuing through old age, there is a gradual change in the
for me? total time we spend sleeping, the percentage of time we spend in REM sleep, and the kinds of sleep problems we have.

Infancy and Adolescence and Adulthood Researchers recently found that, compared to adults, Old Age
Childhood adolescents need more sleep (about 9 hours) and their circadian clocks favor going to Upon reaching our
From infancy to bed later and getting up later (Hathaway, 2006; MFMER, 2005). Researchers concluded sixties, total sleep time
adolescence, the total that adolescents who must get up early (6 or 7 ..) for classes are o en sleep deprived, drops to about 6.5 hours
amount of time spent which may interfere with their performance (L. Epstein & Mardon, 2007; NSF, 2006). a day, but the percentage
in sleep and the per- One solution is for high-school classes to start an hour later so adolescents can get suf- of REM sleep remains
centage spent in REM ficient sleep. At about age 20, adolescents adopt the sleep pattern of adults, which is to about the same (20%)
gradually decline. For get approximately 7–8 hours of sleep a night, with about 20% or less being REM sleep. (Ropper & Samuels,
example, a newborn 2009). In people over 55,
sleeps about 17 hours 66% experience symp-
a day, and 50% of that toms of a sleep problem
time is spent in REM; (trouble getting to sleep
a 4-year-old sleeps or staying asleep, inter-
about 10 hours a rupted breathing), and
day, and 25–30% they compensate by
of that time is spent taking a daytime nap
in REM. (NSF, 2003, 2004).

Why Do I Sleep?
Why we sleep remains one of the greatest mysteries of nature (M. G. Frank, 2006). One reason we know sleep is
Is my important comes from studies of animals who are deprived of sleep. Rats can live about 16 days without food (water

brain being provided) and about 17 days without sleep (Rechtschaffen, 1997). So far, the longest a human has voluntarily gone
without sleep is 11 days (discussed on next page). We’ll explain two currently popular theories—the repair and
repaired? adaptive theories—of why we spend about one-third of each day asleep.

The repair theory suggests that The adaptive theory suggests sleep

activities during the day deplete key evolved because it prevented early

factors in our brain or body that are humans and animals from wasting

replenished or repaired by sleep. The energy and exposing themselves to the

repair theory says that sleep is primarily a dangers of nocturnal predators (W. B.

restorative process. Webb, 1992).

The repair theory is supported Support for the adaptive theory
by three findings. First, during comes from observations that large
sleep there is a marked secre- predatory animals, such as lions,
Repair theory says sleep tion of growth hormone, which controls sleep a lot and wherever they wish, Adaptive theory says sleep
restores brain and body. aspects of metabolism, physical growth, while prey animals, such as antelope, helps us avoid dangers.

and brain development (Pandi-Perumal et al., 2008). Second, during sleep far less and in protected areas. Many birds sleep with one
sleep there is increased production of immune cells to fight infection hemisphere at a time, to guard against predators (Sillery, 2002).
(Barth, 2009; M. R. Irwin et al., 2008). ird, during wakefulness Animals (humans) that rely primarily on visual cues and have lit-
there is a decline in the brain’s energy stores (glycogen), which are tle night vision have evolved a circadian clock for sleeping at night
restored during sleep and needed for normal functioning (Geiger, and thus avoid becoming prey (Hirshkowitz et al., 1997).
2002). e brain needs sleep to grow, repair its immune system, and The adaptive and repair theories are not really at odds. Both
restore its energy and chemicals (J. M. Siegel, 2003). have support but just focus on different reasons for sleep.

156 M O D U L E 7 S L E E P & D R E A M S

What If I Miss Sleep?
One method of investigating why sleep is important is to study people or animals who are sleep deprived. e
Can you go record for sleep deprivation was set by a young adult who went without sleep for 11 days, or 264 hours (L. C.

without sleep? Johnson et al., 1965). On his 11th day without sleep, this young man beat the researcher in a pinball game, which
indicates he was still awake and alert. Here’s what happens when people are sleep deprived.

Effects on the Body Effects on the Brain

Sleep deprivation, even for 264 hours, has minimal effect on Sleep deprivation can deplete the
physiological functions controlled by the autonomic nervous brain’s vital energy stores (gylcogen)
system, such as heart rate or blood pressure (Kato et al., and interfere with completing tasks
2000). However, sleep deprivation can lead to serious health that require vigilance and concentration,
problems. Sleep deprivation may compromise our immune such as recalling and recognizing words and
system, which increases an individual’s vulnerability to viral doing math tests (Geiger, 2002; Ropper &
infections and may lead to inflammation-related diseases Samuels, 2009). Sleep deprivation increases activity of the
(Dement, 1999; M. R. Irwin et al., 2008). Also, sleep deprivation emotional centers of the brain, particularly in response to
puts the body on alert, increasing production of stress hor- negative stimuli, leading to irritability as well as interfer-
mones and elevating blood pressure, which are major risk fac- ing with the ability to make rational or logical decisions
tors for health conditions such as heart disease, stroke, and (Yoo et al., 2007). In a more extreme case of sleep depriva-
cancer (R. Stein, 2005a). Sleep deprivation has been linked to changes in tion, sled-dog racers who averaged 2 hours of sleep a night
appetite-related hormones and elevated amounts of the hormone insulin. during the 12-day Iditarod race reported vivid hallucina-
Researchers concluded that sleep deprivation increases the risk for obesity tions, such as seeing blazing fireplaces, only to awake lying
and diabetes (K. L. Knutson et al., 2007; Van Cauter et al., 2007). in the cold snow (Balzar, 1997).

What Causes Sleep?
A er getting into bed, most of us fall asleep within 5–30 minutes and sleep an average of 7–8 hours (range
How do you about 6–10 hours). Going to sleep involves a very complicated process during which different areas of the

go to sleep? brain are activated or deactivated. e whole sleep process begins with something flipping the master switch

for sleep.

Master Sleep Switch Reticular Formation Going to Sleep
In order for the forebrain to receive
The master and process information from the e master sleep switch and the reticular formation are but
switch for sleep senses, it must be aroused and alerted two of the factors regulating sleep. Here is the probable
is in a nucleus by the reticular formation. sequence for going to sleep.
of the brain First, the time of day you go to sleep is regulated by the
called the VPN circadian clock, which is influenced by the suprachiasmatic
VPN is sleep (Purves et al., nucleus of the hypothalamus (R. Y. Moore, 2006).
switch. 2008). Reticular Second, something turns on your master sleep switch,
formation
The VPN—ventrolateral pre- is turned which is located in the VPN (ventrolateral preoptic nucle-
off to go
optic nucleus—is a group of to sleep. us). In turn, the VPN turns off areas that arouse your brain,

cells in the hypothalamus that act such as the reticular formation (Garcia-Rill et al., 2006).

like a master switch for sleep. Reticular ird, a number of different chemicals and neurotrans-
formation
When turned on, the VPN secretes mitters, some of which are manufactured in the pons,

a neurotransmitter (GABA) that regulate when you go into and out of non-REM and REM

turns off areas that keep the brain The reticular formation, a column of sleep and when you awaken (Czeisler et al., 2006).
cells that stretches the length of the brain
awake. When the VPN is turned stem, arouses and alerts the forebrain and Fourth, the circadian rhythm that regulates your body
prepares it to receive information from all
off, certain brain areas become the senses. temperature is tied in with sleep, since you go to sleep

active and you wake up. e reticular formation is impor- when your temperature
tant in keeping the forebrain alert and
Researchers don’t know in producing a state of wakefulness falls and wake up Four
how the VPN in humans is (Ropper, 2006). If the reticular forma- when your temper- factors
turned on and off, but they tion is stimulated in sleeping animals, ature rises (Ropper for sleep
recently found that the VPN they awaken; if it is seriously damaged & Samuels, 2009).
in rats is activated by the in animals or humans, they lapse into us, the reasons you go to sleep and wake up involve
neurotransmitter adenosine permanent unconsciousness or coma. a complex interaction among the circadian clock, brain
(Gallopin et al., 2005). Next, areas, sleep-inducing chemicals, and body temperature.
we’ll look at one brain area the A er the Concept Review, we’ll describe a psychological
VPN turns off. problem whose cause seems related to decreased sunlight.

E . Q U E S T I O N S A B O U T S L E E P 157

Concept Review

1. The various levels of awareness of waves with bursts of activity that
one’s thoughts and feelings, as well as are called (b) .
of other internal and external stimuli, Stage 3 and especially stage 4 are
are referred to as (a) . marked by high-amplitude, low-
This experience varies on a continuum frequency (c) .
from very aware and alert to totally Stage 4 is often considered the
unaware and unresponsive. Activities deepest stage of sleep because it is the most difficult from which to
that require full awareness and alertness and may interfere with be awakened. During stage 4, heart rate, respiration, temperature,
other ongoing endeavors are called (b) . In and blood flow to the brain are (d) . Together,
comparison, activities that require little awareness and minimal stages 1, 2, 3, and 4 are referred to as (e) , in
attention and that do not interfere with other ongoing endeavors which we spend about 80% of our sleep time. About five or six
are called (c) . times throughout the night, we enter a paradoxical state called
(f) , which accounts for the remaining 20% of
2. The biological clock that is set for our sleep time. This stage is characterized by increased physiologi-
a day of about 24 hours is called a
(a) . This rhythm cal arousal, “alert and awake” brain waves, and vivid dreaming.

regulates our sleep-wake cycle, which 6. From birth through old age, there is a decrease in
total sleep time, from about 17 hours in new-
is set to an average day of 24 hours borns to 6.5 hours after age 60. In addition,
and 18 minutes. Our circadian clock
is reset by 18 minutes each day to match our agreed upon 24-hour one stage of sleep, called ,
decreases from 50% of sleep time in infancy
day. The circadian clock is located in the brain’s hypothalamus, in to 20% in adulthood.
a small part called the (b) .

3. If your circadian rhythm is out of step with 7. There are two different but not incom-
patible theories of why we sleep. The theory
local time, you may feel fatigued and disoriented, that says the purpose of sleep is to restore
a traveler’s complaint called (a) .
Workers and drivers have more accidents dur- factors depleted throughout the day is the
(a) . The theory that says
ing the early-morning hours because their sleep is based on an evolutionary need to
sleep-wake clock is telling them it’s time
to (b) . Researchers have conserve energy and escape nocturnal
harm is the (b) .
reset circadian rhythms by exposing subjects
and night workers to periods of bright light;
this is called (c) therapy. 8. Going to sleep is regulated by the follow-
ing factors. An area in the hypothalamus
that is the master sleep switch is called
4. Near the center of the human brain is the (a) . An area in the
an oval group of cells, collectively called
the pineal gland, that secrete a hormone hypothalamus that regulates circadian
rhythms is called the (b)
called (a) . The gland nucleus. A brain area that contributes to our stay-
secretes the hormone during dark peri-
ods and stops when it gets light. In many animals, this hormone ing awake by sending neural signals that alert and
arouse the forebrain is called the (c) . Several
plays a major role in the regulation of (b) different sleep chemicals and (d) , some of which
rhythms.
are made in the pons, regulate going into and out of the stages of
5. During a night’s sleep, we gradually pass through five stages. sleep. In addition, we go to sleep several hours after a fall in body
Stage 1, which is a transition between waking and sleeping, has (e) and get up when it starts to rise. Photo Credit: (#1) © Michael S. Yamashita/Corbis
brain waves known as (a) . Stage 2 has brain

Answers: 1. (a) consciousness, (b) controlled processes, (c) automatic processes; 2. (a) circadian rhythm, (b) suprachiasmatic nucleus; 3. (a) jet lag,
(b) sleep, (c) light; 4. (a) melatonin, (b) circadian; 5. (a) theta waves, (b) sleep spindles, (c) delta waves, (d) reduced, (e) non-REM sleep, (f) REM
sleep; 6. REM sleep; 7. (a) repair theory, (b) adaptive theory; 8 (a) VPN, or ventrolateral preoptic nucleus, (b) suprachiasmatic, (c) reticular forma-
tion, (d) neurotransmitters, (e) temperature

158 M O D U L E 7 S L E E P & D R E A M S

F. Cultural Diversity: Incidence of SAD

Problem and Treatment
Problem. For many animals, including and craving for carbohydrates. Recently, SAD has become a subtype
Does light humans, sunlight has a direct influence (Seasonal Pattern Specifier) of major depression (American

affect your on resetting the circadian clock and Psychiatric Association, 2000).

mood? affecting circadian rhythms. Cause and Treatment. What might trigger SAD
However, it was only recently that is the amount of a brain neurotransmitter, serotonin,
researchers found a direct nerve connection from recep- and the amount of a hormone made mostly at night,
tors in the retina, which is located in the back of the eye, melatonin. Researchers suggest that the decreased
to a nucleus in the brain (suprachiasmatic nucleus in the sunlight in fall and winter causes a decrease in the
hypothalamus, p. 150). is particular nerve pathway is amount of serotonin and an increase in melatonin,
not involved with seeing things but only with sensing the which may both act to trigger SAD (Anstett, 2006;
presence and amount of light, either sunlight or artificial G. W. Lambert et al., 2002).
light (M. W. Young, 2000). is means that humans have Seasonal affective A nondrug treatment for SAD involves exposing a
a neural pathway that is very responsive to the presence disorder (SAD) occurs
of light and may be involved in a mental health problem person to bright light in the morning for about one
in fall/winter. hour (Westrin & Lam, 2007). is treatment helps as

called seasonal affective disorder, or SAD. many as 70% of individuals diagnosed with SAD (Anstett, 2006).
Because decreased sunlight appears to trigger SAD, you would
Seasonal affective disorder, or SAD, is a pattern of depressive symp-
toms, such as loss of interest or pleasure in nearly all activities. Depressed expect the fewest cases of SAD in southern Florida, more cases in
feelings cycle with the seasons, typically beginning in fall or winter and northern New Hampshire with its gloomy winters, and even more
going away in spring, when days are longer and sunnier. Along with cases in northern Iceland, which has harsh winters with little or
depression are lethargy, excessive sleepiness, overeating, weight gain, no sunlight.

Occurrence of SAD
As predicted, the graph When researchers try to explain
Where is the shows that the incidence any unusual or unpredicted find-
highest rate of SAD is very low (1.4%) % SAD ings, they first check the methods
of SAD? among people who live 1.4 in Florida and procedures used to measure the

in sunny Florida but 3.6 % SAD dependent variable, which in this case
about five times higher (7.3%) among people in Iceland is the occurrence of SAD. However,

who live under the gray winter skies of north- 7.3 % SAD in researchers in Iceland used the same
ern New Hampshire (Magnusson, 2000). New Hampshire methods (questionnaires) and proce-

However, far north of New Hampshire is dures that were used by researchers in
Iceland (see map), which has far less sunlight in the United States (Magnusson, 2000).
fall and winter than New Hampshire. In spite of having less sun- If research methods and procedures were similar, what else would
light, Icelanders have only about half the incidence of SAD (3.6%) explain why the highest incidence of SAD was reported in New
compared to residents of New Hampshire (Axelsson et al., 2002). Hampshire and not in Iceland?

Cultural Differences Another explanation for
Why did Icelanders report less than half the incidence of SAD,
What’s even though they have far less sunlight in fall and winter Icelanders’ low incidence of

different about than residents of New Hampshire (see map)? SAD may involve genetic fac-
Researchers concluded that differences in Iceland tors. For example, research-
Icelanders? methods, questionnaires, and residents’ AtOlacnetaicn Mid ers studied a population of

lifestyles or occupations could not explain this discrep- immigrants in Canada who were wholly
ancy. Rather, there may be two other explanations of Icelandic descent. e incidence of SAD in
Photo Credit: © DigitalStock Corporation that involve cultural and genetic differences. ScNootivaa the Icelandic immigrants was unexpectedly much

For 1,000 years, Icelanders have lived rather New lower than found in other residents of the same general
isolated in a very demanding, low-sunlight envi- Hampshire area. Researchers concluded that the lower frequency of

ronment. Because of very harsh and unyielding SAD in Icelanders is puzzling and may reflect both genetic
environmental demands, Icelanders may have and cultural differences, such as learning how to deal with iso-
developed an emotional hardiness to deal with Cultural differences lation and living in harsh environments (Axelsson et al., 2002;
explain why Iceland
especially gloomy winters that trigger almost (far north) has Magnusson & Partonen, 2005).
twice as many cases of SAD among residents of the less SAD than Next, we’ll discuss four explanations for something most of
northeastern United States. New Hampshire.
us experience every night—dreaming.

F. C U L T U R A L D I V E R S I T Y : I N C I D E N C E O F S A D 159