psychological science disscussions

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Chapter 4

Sensing and Perceiving Misperception by Those Trained to Accurately Perceive a Threat

On September 6, 2007, the Asia-Pacific Economic Cooperation (APEC) leaders’ summit was being held in downtown

Sydney, Australia. World leaders, including the then-current U.S. president, George W. Bush, were attending the

summit. Many roads in the area were closed for security reasons, and police presence was high.

As a prank, eight members of the Australian television satire The Chaser’s War on Everything assembled a false

motorcade made up of two black four-wheel-drive vehicles, a black sedan, two motorcycles, body guards, and

chauffeurs (see the video below). Group member Chas Licciardello was in one of the cars disguised as Osama bin

Laden. The motorcade drove through Sydney’s central business district and entered the security zone of the meeting.

The motorcade was waved on by police, through two checkpoints, until the Chaser group decided it had taken the gag

far enough and stopped outside the InterContinental Hotel where former President Bush was staying. Licciardello

stepped out onto the street and complained, in character as bin Laden, about not being invited to the APEC Summit.

Only at this time did the police belatedly check the identity of the group members, finally arresting them.

Chaser APEC Motorcade Stunt

Motorcade Stunt performed by the Chaser pranksters in 2007.

Afterward, the group testified that it had made little effort to disguise its attempt as anything more than a prank. The

group’s only realistic attempt to fool police was its Canadian-flag marked vehicles. Other than that, the group used

obviously fake credentials, and its security passes were printed with “JOKE,” “Insecurity,” and “It’s pretty obvious this

isn’t a real pass,” all clearly visible to any police officer who might have been troubled to look closely as the motorcade

passed. The required APEC 2007 Official Vehicle stickers had the name of the group’s show printed on them, and this

text: “This dude likes trees and poetry and certain types of carnivorous plants excite him.” In addition, a few of the

“bodyguards” were carrying camcorders, and one of the motorcyclists was dressed in jeans, both details that should

have alerted police that something was amiss.

The Chaser pranksters later explained the primary reason for the stunt. They wanted to make a statement about the

fact that bin Laden, a world leader, had not been invited to an APEC Summit where issues of terror were being

discussed. The secondary motive was to test the event’s security. The show’s lawyers approved the stunt, under the

assumption that the motorcade would be stopped at the APEC meeting.

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The ability to detect and interpret the events that are occurring around us allows us to respond to

these stimuli appropriately (Gibson & Pick, 2000). [1]

In most cases the system is successful, but

as you can see from the above example, it is not perfect. In this chapter we will discuss the

strengths and limitations of these capacities, focusing on both sensation—awareness resulting

from the stimulation of a sense organ, and perception—the organization and interpretation of

sensations. Sensation and perception work seamlessly together to allow us to experience the

world through our eyes, ears, nose, tongue, and skin, but also to combine what we are currently

learning from the environment with what we already know about it to make judgments and to

choose appropriate behaviors.

The study of sensation and perception is exceedingly important for our everyday lives because

the knowledge generated by psychologists is used in so many ways to help so many people.

Psychologists work closely with mechanical and electrical engineers, with experts in defense and

military contractors, and with clinical, health, and sports psychologists to help them apply this

knowledge to their everyday practices. The research is used to help us understand and better

prepare people to cope with such diverse events as driving cars, flying planes, creating robots,

and managing pain (Fajen & Warren, 2003). [2]

We will begin the chapter with a focus on the six senses of seeing, hearing,

smelling, touching, tasting, and monitoring the body’s positions (proprioception). We will see

that sensation is sometimes relatively direct, in the sense that the wide variety of stimuli around

us inform and guide our behaviors quickly and accurately, but nevertheless is always the result of

at least some interpretation. We do not directly experience stimuli, but rather we experience

those stimuli as they are created by our senses. Each sense accomplishes the basic process

of transduction—the conversion of stimuli detected by receptor cells to electrical impulses that

are then transported to the brain—in different, but related, ways.

After we have reviewed the basic processes of sensation, we will turn to the topic of perception,

focusing on how the brain’s processing of sensory experience can not only help us make quick

and accurate judgments, but also mislead us into making perceptual and judgmental errors, such

as those that allowed the Chaser group to breach security at the APEC meeting.

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[1] Gibson, E. J., & Pick, A. D. (2000). An ecological approach to perceptual learning and development. New York, NY: Oxford

University Press.

[2] Fajen, B. R., & Warren, W. H. (2003). Behavioral dynamics of steering, obstacle avoidance, and route selection. Journal of

Experimental Psychology: Human Perception and Performance, 29(2), 343–362.

4.1 We Experience Our World Through Sensation L E A R N I N G O B J E C T I V E S

1. Review and summarize the capacities and limitations of human sensation.

2. Explain the difference between sensation and perception and describe how psychologists measure sensory and

difference thresholds.

Sensory Thresholds: What Can We Experience?

Humans possess powerful sensory capacities that allow us to sense the kaleidoscope of sights,

sounds, smells, and tastes that surround us. Our eyes detect light energy and our ears pick up

sound waves. Our skin senses touch, pressure, hot, and cold. Our tongues react to the molecules

of the foods we eat, and our noses detect scents in the air. The human perceptual system is wired

for accuracy, and people are exceedingly good at making use of the wide variety of information

available to them (Stoffregen & Bardy, 2001). [1]

In many ways our senses are quite remarkable. The human eye can detect the equivalent of a

single candle flame burning 30 miles away and can distinguish among more than 300,000

different colors. The human ear can detect sounds as low as 20 hertz (vibrations per second) and

as high as 20,000 hertz, and it can hear the tick of a clock about 20 feet away in a quiet room.

We can taste a teaspoon of sugar dissolved in 2 gallons of water, and we are able to smell one

drop of perfume diffused in a three-room apartment. We can feel the wing of a bee on our cheek

dropped from 1 centimeter above (Galanter, 1962). [2]

Link

To get an idea of the range of sounds that the human ear can sense, try testing your hearing here:

http://test-my-hearing.com

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Although there is much that we do sense, there is even more that we do not. Dogs, bats, whales,

and some rodents all have much better hearing than we do, and many animals have a far richer

sense of smell. Birds are able to see the ultraviolet light that we cannot (see Figure 4.3

"Ultraviolet Light and Bird Vision") and can also sense the pull of the earth’s magnetic field.

Cats have an extremely sensitive and sophisticated sense of touch, and they are able to navigate

in complete darkness using their whiskers. The fact that different organisms have different

sensations is part of their evolutionary adaptation. Each species is adapted to sensing the things

that are most important to them, while being blissfully unaware of the things that don’t matter.

Measuring Sensation

Psychophysics is the branch of psychology that studies the effects of physical stimuli on sensory

perceptions and mental states. The field of psychophysics was founded by the German

psychologist Gustav Fechner (1801–1887), who was the first to study the relationship between

the strength of a stimulus and a person’s ability to detect the stimulus.

The measurement techniques developed by Fechner and his colleagues are designed in part to

help determine the limits of human sensation. One important criterion is the ability to detect very

faint stimuli. The absolute threshold of a sensation is defined as the intensity of a stimulus that

allows an organism to just barely detect it.

In a typical psychophysics experiment, an individual is presented with a series of trials in which

a signal is sometimes presented and sometimes not, or in which two stimuli are presented that are

either the same or different. Imagine, for instance, that you were asked to take a hearing test. On

each of the trials your task is to indicate either ―yes‖ if you heard a sound or ―no‖ if you did not.

The signals are purposefully made to be very faint, making accurate judgments difficult.

The problem for you is that the very faint signals create uncertainty. Because our ears are

constantly sending background information to the brain, you will sometimes think that you heard

a sound when none was there, and you will sometimes fail to detect a sound that is there. Your

task is to determine whether the neural activity that you are experiencing is due to the

background noise alone or is a result of a signal within the noise.

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The responses that you give on the hearing test can be analyzed using signal detection

analysis. Signal detection analysis is a technique used to determine the ability of the perceiver to

separate true signals from background noise (Macmillan & Creelman, 2005; Wickens,

2002). [3]

As you can see in Figure 4.4 "Outcomes of a Signal Detection Analysis", each

judgment trial creates four possible outcomes: A hit occurs when you, as the listener, correctly

say ―yes‖ when there was a sound. A false alarm occurs when you respond ―yes‖ to no signal. In

the other two cases you respond ―no‖—either amiss (saying ―no‖ when there was a signal) or

a correct rejection (saying ―no‖ when there was in fact no signal).

Figure 4.4 Outcomes of a Signal Detection Analysis

Our ability to accurately detect stimuli is measured using a signal detection analysis. Two of the possible decisions

(hits and correct rejections) are accurate; the other two (misses and false alarms) are errors.

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The analysis of the data from a psychophysics experiment creates two measures. One measure,

known as sensitivity, refers to the true ability of the individual to detect the presence or absence

of signals. People who have better hearing will have higher sensitivity than will those with

poorer hearing. The other measure, response bias, refers to a behavioral tendency to respond

―yes‖ to the trials, which is independent of sensitivity.

Imagine for instance that rather than taking a hearing test, you are a soldier on guard duty, and

your job is to detect the very faint sound of the breaking of a branch that indicates that an enemy

is nearby. You can see that in this case making a false alarm by alerting the other soldiers to the

sound might not be as costly as a miss (a failure to report the sound), which could be deadly.

Therefore, you might well adopt a very lenient response bias in which whenever you are at all

unsure, you send a warning signal. In this case your responses may not be very accurate (your

sensitivity may be low because you are making a lot of false alarms) and yet the extreme

response bias can save lives.

Another application of signal detection occurs when medical technicians study body images for

the presence of cancerous tumors. Again, a miss (in which the technician incorrectly determines

that there is no tumor) can be very costly, but false alarms (referring patients who do not have

tumors to further testing) also have costs. The ultimate decisions that the technicians make are

based on the quality of the signal (clarity of the image), their experience and training (the ability

to recognize certain shapes and textures of tumors), and their best guesses about the relative costs

of misses versus false alarms.

Although we have focused to this point on the absolute threshold, a second important criterion

concerns the ability to assess differences between stimuli.

The difference threshold (or just noticeable difference [JND]), refers to the change in a stimulus

that can just barely be detected by the organism.The German physiologist Ernst Weber (1795–

1878) made an important discovery about the JND—namely, that the ability to detect differences

depends not so much on the size of the difference but on the size of the difference in relationship

to the absolute size of the stimulus. Weber’s law maintains that the just noticeable difference of a

stimulus is a constant proportion of the original intensity of the stimulus. As an example, if you

have a cup of coffee that has only a very little bit of sugar in it (say 1 teaspoon), adding another

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teaspoon of sugar will make a big difference in taste. But if you added that same teaspoon to a

cup of coffee that already had 5 teaspoons of sugar in it, then you probably wouldn’t taste the

difference as much (in fact, according to Weber’s law, you would have to add 5 more teaspoons

to make the same difference in taste).

One interesting application of Weber’s law is in our everyday shopping behavior. Our tendency

to perceive cost differences between products is dependent not only on the amount of money we

will spend or save, but also on the amount of money saved relative to the price of the purchase. I

would venture to say that if you were about to buy a soda or candy bar in a convenience store

and the price of the items ranged from $1 to $3, you would think that the $3 item cost ―a lot

more‖ than the $1 item. But now imagine that you were comparing between two music systems,

one that cost $397 and one that cost $399. Probably you would think that the cost of the two

systems was ―about the same,‖ even though buying the cheaper one would still save you $2.

Research Focus: Influence without Awareness

If you study Figure 4.5 "Absolute Threshold", you will see that the absolute threshold is the point where we become

aware of a faint stimulus. After that point, we say that the stimulus is conscious because we can accurately report on

its existence (or its nonexistence) better than 50% of the time. But can subliminal stimuli (events that occur below the

absolute threshold and of which we are not conscious) have an influence on our behavior?

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Figure 4.5Absolute Threshold

As the intensity of a stimulus increases, we are more likely to perceive it. Stimuli below the absolute threshold can

still have at least some influence on us, even though we cannot consciously detect them.

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A variety of research programs have found that subliminal stimuli can influence our judgments

and behavior, at least in the short term (Dijksterhuis, 2010). [4]

But whether the presentation of

subliminal stimuli can influence the products that we buy has been a more controversial topic in

psychology. In one relevant experiment, Karremans, Stroebe, and Claus (2006) [5]

had Dutch

college students view a series of computer trials in which a string of letters such

as BBBBBBBBB or BBBbBBBBB were presented on the screen. To be sure they paid attention to

the display, the students were asked to note whether the strings contained a small b. However,

immediately before each of the letter strings, the researchers presented either the name of a drink

that is popular in Holland (Lipton Ice) or a control string containing the same letters as Lipton

Ice (NpeicTol). These words were presented so quickly (for only about one fiftieth of a second)

that the participants could not see them.

Then the students were asked to indicate their intention to drink Lipton Ice by answering

questions such as ―If you would sit on a terrace now, how likely is it that you would order Lipton

Ice,‖ and also to indicate how thirsty they were at the time. The researchers found that the

students who had been exposed to the ―Lipton Ice‖ words (and particularly those who indicated

that they were already thirsty) were significantly more likely to say that they would drink Lipton

Ice than were those who had been exposed to the control words.

If it were effective, procedures such as this (we can call the technique ―subliminal advertising‖

because it advertises a product outside awareness) would have some major advantages for

advertisers, because it would allow them to promote their products without directly interrupting

the consumers’ activity and without the consumers’ knowing they are being persuaded. People

cannot counterargue with, or attempt to avoid being influenced by, messages received outside

awareness. Due to fears that people may be influenced without their knowing, subliminal

advertising has been legally banned in many countries, including Australia, Great Britain, and

the United States.

Although it has been proven to work in some research, subliminal advertising’s effectiveness is

still uncertain. Charles Trappey (1996) [6]

conducted a meta-analysis in which he combined 23

leading research studies that had tested the influence of subliminal advertising on consumer

choice. The results of his meta-analysis showed that subliminal advertising had a negligible

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effect on consumer choice. And Saegert (1987, p. 107) [7]

concluded that ―marketing should quit

giving subliminal advertising the benefit of the doubt,‖ arguing that the influences of subliminal

stimuli are usually so weak that they are normally overshadowed by the person’s own decision

making about the behavior.

Taken together then, the evidence for the effectiveness of subliminal advertising is weak, and its

effects may be limited to only some people and in only some conditions. You probably don’t

have to worry too much about being subliminally persuaded in your everyday life, even if

subliminal ads are allowed in your country. But even if subliminal advertising is not all that

effective itself, there are plenty of other indirect advertising techniques that are used and that do

work. For instance, many ads for automobiles and alcoholic beverages are subtly sexualized,

which encourages the consumer to indirectly (even if not subliminally) associate these products

with sexuality. And there is the ever more frequent ―product placement‖ techniques, where

images of brands (cars, sodas, electronics, and so forth) are placed on websites and in popular

television shows and movies. Harris, Bargh, & Brownell (2009) [8]

found that being exposed to

food advertising on television significantly increased child and adult snacking behaviors, again

suggesting that the effects of perceived images, even if presented above the absolute threshold,

may nevertheless be very subtle.

Another example of processing that occurs outside our awareness is seen when certain areas of

the visual cortex are damaged, causing blindsight, a condition in which people are unable to

consciously report on visual stimuli but nevertheless are able to accurately answer questions

about what they are seeing. When people with blindsight are asked directly what stimuli look

like, or to determine whether these stimuli are present at all, they cannot do so at better than

chance levels. They report that they cannot see anything. However, when they are asked more

indirect questions, they are able to give correct answers. For example, people with blindsight are

able to correctly determine an object’s location and direction of movement, as well as identify

simple geometrical forms and patterns (Weiskrantz, 1997). [9]

It seems that although conscious

reports of the visual experiences are not possible, there is still a parallel and implicit process at

work, enabling people to perceive certain aspects of the stimuli.

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K E Y T A K E A W A Y S

 Sensation is the process of receiving information from the environment through our sensory organs. Perception is the

process of interpreting and organizing the incoming information in order that we can understand it and react

accordingly.

 Transduction is the conversion of stimuli detected by receptor cells to electrical impulses that are transported to the

brain.

 Although our experiences of the world are rich and complex, humans—like all species—have their own adapted

sensory strengths and sensory limitations.

 Sensation and perception work together in a fluid, continuous process.

 Our judgments in detection tasks are influenced by both the absolute threshold of the signal as well as our current

motivations and experiences. Signal detection analysis is used to differentiate sensitivity from response biases.

 The difference threshold, or just noticeable difference, is the ability to detect the smallest change in a stimulus about

50% of the time. According to Weber’s law, the just noticeable difference increases in proportion to the total intensity

of the stimulus.

 Research has found that stimuli can influence behavior even when they are presented below the absolute threshold

(i.e., subliminally). The effectiveness of subliminal advertising, however, has not been shown to be of large magnitude.

E X E R C I S E S A N D C R I T I C A L T H I N K I N G

1. The accidental shooting of one’s own soldiers (friendly fire) frequently occurs in wars. Based on what you have

learned about sensation, perception, and psychophysics, why do you think soldiers might mistakenly fire on their own

soldiers?

2. If we pick up two letters, one that weighs 1 ounce and one that weighs 2 ounces, we can notice the difference. But if

we pick up two packages, one that weighs 3 pounds 1 ounce and one that weighs 3 pounds 2 ounces, we can’t tell the

difference. Why?

3. Take a moment and lie down quietly in your bedroom. Notice the variety and levels of what you can see, hear, and

feel. Does this experience help you understand the idea of the absolute threshold?

[1] Stoffregen, T. A., & Bardy, B. G. (2001). On specification and the senses. Behavioral and Brain Sciences, 24(2), 195–261.

[2] Galanter, E. (1962). Contemporary Psychophysics. In R. Brown, E. Galanter, E. H. Hess, & G. Mandler (Eds.), New directions in

psychology. New York, NY: Holt, Rinehart and Winston.

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[3] Macmillan, N. A., & Creelman, C. D. (2005). Detection theory: A user’s guide (2nd ed). Mahwah, NJ: Lawrence Erlbaum

Associates; Wickens, T. D. (2002). Elementary signal detection theory. New York, NY: Oxford University Press.

[4] Dijksterhuis, A. (2010). Automaticity and the unconscious. In S. T. Fiske, D. T. Gilbert, & G. Lindzey (Eds.), Handbook of social

psychology (5th ed., Vol. 1, pp. 228–267). Hoboken, NJ: John Wiley & Sons.

[5] Karremans, J. C., Stroebe, W., & Claus, J. (2006). Beyond Vicary’s fantasies: The impact of subliminal priming and brand

choice. Journal of Experimental Social Psychology, 42(6), 792–798.

[6] Trappey, C. (1996). A meta-analysis of consumer choice and subliminal advertising.Psychology and Marketing, 13, 517–530.

[7] Saegert, J. (1987). Why marketing should quit giving subliminal advertising the benefit of the doubt. Psychology and

Marketing, 4(2), 107–120.

[8] Harris, J. L., Bargh, J. A., & Brownell, K. D. (2009). Priming effects of television food advertising on eating behavior. Health

Psychology, 28(4), 404–413.

[9] Weiskrantz, L. (1997). Consciousness lost and found: A neuropsychological exploration.New York, NY: Oxford University

Press.

4.2 Seeing L E A R N I N G O B J E C T I V E S

1. Identify the key structures of the eye and the role they play in vision.

2. Summarize how the eye and the visual cortex work together to sense and perceive the visual stimuli in the

environment, including processing colors, shape, depth, and motion.

Whereas other animals rely primarily on hearing, smell, or touch to understand the world around

them, human beings rely in large part on vision. A large part of our cerebral cortex is devoted to

seeing, and we have substantial visual skills. Seeing begins when light falls on the eyes, initiating

the process of transduction. Once this visual information reaches the visual cortex, it is processed

by a variety of neurons that detect colors, shapes, and motion, and that create meaningful

perceptions out of the incoming stimuli.

The air around us is filled with a sea of electromagnetic energy; pulses of energy waves that can

carry information from place to place. As you can see in Figure 4.6 "The Electromagnetic

Spectrum", electromagnetic waves vary in their wavelength—the distance between one wave

peak and the next wave peak, with the shortest gamma waves being only a fraction of a

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millimeter in length and the longest radio waves being hundreds of kilometers long. Humans are

blind to almost all of this energy—our eyes detect only the range from about 400 to 700

billionths of a meter, the part of the electromagnetic spectrum known as the visible spectrum.

Figure 4.6 The Electromagnetic Spectrum

Only a small fraction of the electromagnetic energy that surrounds us (the visible spectrum) is detectable by the

human eye.

The Sensing Eye and the Perceiving Visual Cortex

As you can see in Figure 4.7 "Anatomy of the Human Eye", light enters the eye through

the cornea, a clear covering that protects the eye and begins to focus the incoming light. The

light then passes through the pupil, a small opening in the center of the eye. The pupil is

surrounded by the iris, the colored part of the eye that controls the size of the pupil by

constricting or dilating in response to light intensity. When we enter a dark movie theater on a

sunny day, for instance, muscles in the iris open the pupil and allow more light to enter.

Complete adaptation to the dark may take up to 20 minutes.

Behind the pupil is the lens, a structure that focuses the incoming light on the retina, the layer of

tissue at the back of the eye that contains photoreceptor cells. As our eyes move from near

objects to distant objects, a process known as visual

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accommodation occurs. Visual accommodation is the process of changing the curvature of the

lens to keep the light entering the eye focused on the retina. Rays from the top of the image strike

the bottom of the retina and vice versa, and rays from the left side of the image strike the right

part of the retina and vice versa, causing the image on the retina to be upside down and

backward. Furthermore, the image projected on the retina is flat, and yet our final perception of

the image will be three dimensional.

Figure 4.7 Anatomy of the Human Eye

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Light enters the eye through the transparent cornea, passing through the pupil at the center of the iris. The lens

adjusts to focus the light on the retina, where it appears upside down and backward. Receptor cells on the retina

send information via the optic nerve to the visual cortex.

Accommodation is not always perfect, and in some cases the light that is hitting the retina is a bit

out of focus. As you can see in Figure 4.8 "Normal, Nearsighted, and Farsighted Eyes", if the

focus is in front of the retina, we say that the person is nearsighted, and when the focus is behind

the retina we say that the person is farsighted. Eyeglasses and contact lenses correct this problem

by adding another lens in front of the eye, and laser eye surgery corrects the problem by

reshaping the eye’s own lens.

Figure 4.8 Normal, Nearsighted, and Farsighted Eyes

For people with normal vision (left), the lens properly focuses incoming light on the retina. For people who are

nearsighted (center), images from far objects focus too far in front of the retina, whereas for people who are

farsighted (right), images from near objects focus too far behind the retina. Eyeglasses solve the problem by adding

a secondary, corrective, lens.

The retina contains layers of neurons specialized to respond to light (see Figure 4.9 "The Retina

With Its Specialized Cells"). As light falls on the retina, it first activates receptor cells known

as rods and cones. The activation of these cells then spreads to the bipolar cells and then to

the ganglion cells, which gather together and converge, like the strands of a rope, forming

the optic nerve. The optic nerve is a collection of millions of ganglion neurons that sends vast

amounts of visual information, via the thalamus, to the brain. Because the retina and the optic

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nerve are active processors and analyzers of visual information, it is not inappropriate to think of

these structures as an extension of the brain itself.

Figure 4.9 The Retina With Its Specialized Cells

When light falls on the retina, it creates a photochemical reaction in the rods and cones at the back of the retina. The

reactions then continue to the bipolar cells, the ganglion cells, and eventually to the optic nerve.

Rods are visual neurons that specialize in detecting black, white, and gray colors. There are

about 120 million rods in each eye. The rods do not provide a lot of detail about the images we

see, but because they are highly sensitive to shorter-waved (darker) and weak light, they help us

see in dim light, for instance, at night. Because the rods are located primarily around the edges of

the retina, they are particularly active in peripheral vision (when you need to see something at

night, try looking away from what you want to see). Cones are visual neurons that are

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specialized in detecting fine detail and colors. The 5 million or so cones in each eye enable us to

see in color, but they operate best in bright light. The cones are located primarily in and around

the fovea, which is the central point of the retina.

To demonstrate the difference between rods and cones in attention to detail, choose a word in

this text and focus on it. Do you notice that the words a few inches to the side seem more

blurred? This is because the word you are focusing on strikes the detail-oriented cones, while the

words surrounding it strike the less-detail-oriented rods, which are located on the periphery.

As you can see in Figure 4.11 "Pathway of Visual Images Through the Thalamus and Into the

Visual Cortex", the sensory information received by the retina is relayed through the thalamus to

corresponding areas in the visual cortex, which is located in the occipital lobe at the back of the

brain. Although the principle of contralateral control might lead you to expect that the left eye

would send information to the right brain hemisphere and vice versa, nature is smarter than that.

In fact, the left and right eyes each send information to both the left and the right hemisphere,

and the visual cortex processes each of the cues separately and in parallel. This is an adaptational

advantage to an organism that loses sight in one eye, because even if only one eye is functional,

both hemispheres will still receive input from it.

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Figure 4.11 Pathway of Visual Images Through the Thalamus and Into the Visual Cortex

The left and right eyes each send information to both the left and the right brain hemisphere.

The visual cortex is made up of specialized neurons that turn the sensations they receive from the

optic nerve into meaningful images. Because there are no photoreceptor cells at the place where

the optic nerve leaves the retina, a hole or blind spot in our vision is created (see Figure 4.12

"Blind Spot Demonstration"). When both of our eyes are open, we don’t experience a problem

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because our eyes are constantly moving, and one eye makes up for what the other eye misses.

But the visual system is also designed to deal with this problem if only one eye is open—the

visual cortex simply fills in the small hole in our vision with similar patterns from the

surrounding areas, and we never notice the difference. The ability of the visual system to cope

with the blind spot is another example of how sensation and perception work together to create

meaningful experience.

Figure 4.12 Blind Spot Demonstration

You can get an idea of the extent of your blind spot (the place where the optic nerve leaves the retina) by trying this

demonstration. Close your left eye and stare with your right eye at the cross in the diagram. You should be able to

see the elephant image to the right (don’t look at it, just notice that it is there). If you can’t see the elephant, move

closer or farther away until you can. Now slowly move so that you are closer to the image while you keep looking at

the cross. At one distance (probably a foot or so), the elephant will completely disappear from view because its

image has fallen on the blind spot.

Perception is created in part through the simultaneous action of thousands of

feature detector neurons—specialized neurons, located in the visual cortex, that respond to the

strength, angles, shapes, edges, and movements of a visual stimulus (Kelsey, 1997; Livingstone

& Hubel, 1988). [2]

The feature detectors work in parallel, each performing a specialized

function. When faced with a red square, for instance, the parallel line feature detectors, the

horizontal line feature detectors, and the red color feature detectors all become activated. This

activation is then passed on to other parts of the visual cortex where other neurons compare the

information supplied by the feature detectors with images stored in memory. Suddenly, in a flash

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of recognition, the many neurons fire together, creating the single image of the red square that

we experience (Rodriguez et al., 1999). [3]

Figure 4.13 The Necker Cube

The Necker cube is an example of how the visual system creates perceptions out of sensations. We do not see a series

of lines, but rather a cube. Which cube we see varies depending on the momentary outcome of perceptual processes

in the visual cortex.

Some feature detectors are tuned to selectively respond to particularly important objects, for

instance, faces, smiles, and other parts of the body (Downing, Jiang, Shuman, & Kanwisher,

2001; Haxby et al., 2001). [4]

When researchers disrupted face recognition areas of the cortex

using the magnetic pulses of transcranial magnetic stimulation (TMS), people were temporarily

unable to recognize faces, and yet they were still able to recognize houses (McKone, Kanwisher,

& Duchaine, 2007; Pitcher, Walsh, Yovel, & Duchaine, 2007). [5]

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Perceiving Color

It has been estimated that the human visual system can detect and discriminate among 7 million

color variations (Geldard, 1972), [6]

but these variations are all created by the combinations of the

three primary colors: red, green, and blue. The shade of a color, known as hue, is conveyed by

the wavelength of the light that enters the eye (we see shorter wavelengths as more blue and

longer wavelengths as more red), and we detect brightness from the intensity or height of the

wave (bigger or more intense waves are perceived as brighter).

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Figure 4.14 Low- and High-Frequency Sine Waves and Low- and High-Intensity Sine Waves and Their

Corresponding Colors

Light waves with shorter frequencies are perceived as more blue than red; light waves with higher intensity are

seen as brighter.

In his important research on color vision, Hermann von Helmholtz (1821–1894) theorized that

color is perceived because the cones in the retina come in three types. One type of cone reacts

primarily to blue light (short wavelengths), another reacts primarily to green light (medium

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wavelengths), and a third reacts primarily to red light (long wavelengths). The visual cortex then

detects and compares the strength of the signals from each of the three types of cones, creating

the experience of color. According to this Young-Helmholtz trichromatic color theory, what

color we see depends on the mix of the signals from the three types of cones. If the brain is

receiving primarily red and blue signals, for instance, it will perceive purple; if it is receiving

primarily red and green signals it will perceive yellow; and if it is receiving messages from all

three types of cones it will perceive white.

The different functions of the three types of cones are apparent in people who

experience color blindness—the inability to detect either green and/or red colors. About 1 in 50

people, mostly men, lack functioning in the red- or green-sensitive cones, leaving them only able

to experience either one or two colors (Figure 4.15).

Figure 4.15

People with normal color vision can see the number 42 in the first image and the number 12 in the second (they are

vague but apparent). However, people who are color blind cannot see the numbers at all.

Source: Courtesy

ofhttp://commons.wikimedia.org/wiki/File:Ishihara_11.PNG andhttp://commons.wikimedia.org/wiki/File:Ishiha

ra_23.PNG.

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The trichromatic color theory cannot explain all of human vision, however. For one, although the

color purple does appear to us as a mixing of red and blue, yellow does not appear to be a mix of

red and green. And people with color blindness, who cannot see either green or red, nevertheless

can still see yellow. An alternative approach to the Young-Helmholtz theory, known as the

opponent-process color theory, proposes that we analyze sensory information not in terms of

three colors but rather in three sets of “opponent colors”: red-green, yellow-blue, and white-

black. Evidence for the opponent-process theory comes from the fact that some neurons in the

retina and in the visual cortex are excited by one color (e.g., red) but inhibited by another color

(e.g., green).

One example of opponent processing occurs in the experience of an afterimage. If you stare at

the flag on the left side of Figure 4.16 "U.S. Flag" for about 30 seconds (the longer you look, the

better the effect), and then move your eyes to the blank area to the right of it, you will see the

afterimage. When we stare at the green stripes, our green receptors habituate and begin to

process less strongly, whereas the red receptors remain at full strength. When we switch our

gaze, we see primarily the red part of the opponent process. Similar processes create blue after

yellow and white after black.

Figure 4.16 U.S. Flag

The presence of an afterimage is best explained by the opponent-process theory of color perception. Stare at the flag

for a few seconds, and then move your gaze to the blank space next to it. Do you see the afterimage?

Source: Photo courtesy of Mike Swanson,http://en.wikipedia.org/wiki/File:US_flag(inverted).svg.

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The tricolor and the opponent-process mechanisms work together to produce color vision. When

light rays enter the eye, the red, blue, and green cones on the retina respond in different degrees,

and send different strength signals of red, blue, and green through the optic nerve. The color

signals are then processed both by the ganglion cells and by the neurons in the visual cortex

(Gegenfurtner & Kiper, 2003). [7]

Perceiving Form

One of the important processes required in vision is the perception of form. German

psychologists in the 1930s and 1940s, including Max Wertheimer (1880–1943), Kurt Koffka

(1886–1941), and Wolfgang Köhler (1887–1967), argued that we create forms out of their

component sensations based on the idea of the gestalt, a meaningfully organized whole. The idea

of the gestalt is that the ―whole is more than the sum of its parts.‖ Some examples of how gestalt

principles lead us to see more than what is actually there are summarized inTable 4.1 "Summary

of Gestalt Principles of Form Perception".

Table 4.1 Summary of Gestalt Principles of Form Perception

Principle Description Example Image

Figure and

ground

We structure

input such that

we always see a

figure (image)

against a ground

(background).

At right, you may see a vase

or you may see two faces,

but in either case, you will

organize the image as a

figure against a ground. Figure 4.1

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Principle Description Example Image

Similarity

Stimuli that are

similar to each

other tend to be

grouped together.

You are more likely to see

three similar columns among

the XYXcharacters at right

than you are to see four

rows.

Figure 4.1

Proximity

We tend to group

nearby figures

together.

Do you see four or eight

images at right? Principles of

proximity suggest that you

might see only four. Figure 4.1

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Principle Description Example Image

Continuity

We tend to

perceive stimuli

in smooth,

continuous ways

rather than in

more

discontinuous

ways.

At right, most people see a

line of dots that moves from

the lower left to the upper

right, rather than a line that

moves from the left and then

suddenly turns down. The

principle of continuity leads

us to see most lines as

following the smoothest

possible path.

Figure 4.1

Closure

We tend to fill in

gaps in an

incomplete image

to create a

complete, whole

Closure leads us to see a

single spherical object at

right rather than a set of

unrelated cones. Figure 4.1

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Principle Description Example Image

object.

Perceiving Depth

Depth perception is the ability to perceive three-dimensional space and to accurately judge

distance. Without depth perception, we would be unable to drive a car, thread a needle, or simply

navigate our way around the supermarket (Howard & Rogers, 2001). [8]

Research has found that

depth perception is in part based on innate capacities and in part learned through experience

(Witherington, 2005). [9]

Psychologists Eleanor Gibson and Richard Walk (1960) [10]

tested the ability to perceive depth in

6- to 14-month-old infants by placing them on a visual cliff,a mechanism that gives the

perception of a dangerous drop-off, in which infants can be safely tested for their perception of

depth (Figure 4.22 "Visual Cliff"). The infants were placed on one side of the ―cliff,‖ while their

mothers called to them from the other side. Gibson and Walk found that most infants either

crawled away from the cliff or remained on the board and cried because they wanted to go to

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their mothers, but the infants perceived a chasm that they instinctively could not cross. Further

research has found that even very young children who cannot yet crawl are fearful of heights

(Campos, Langer, & Krowitz, 1970). [11]

On the other hand, studies have also found that infants

improve their hand-eye coordination as they learn to better grasp objects and as they gain more

experience in crawling, indicating that depth perception is also learned (Adolph, 2000). [12]

Depth perception is the result of our use of depth cues, messages from our bodies and the

external environment that supply us with information about space and distance.

Binocular depth cues are depth cues that are created by retinal image disparity—that is, the

space between our eyes, and thus which require the coordination of both eyes. One outcome of

retinal disparity is that the images projected on each eye are slightly different from each other.

The visual cortex automatically merges the two images into one, enabling us to perceive depth.

Three-dimensional movies make use of retinal disparity by using 3-D glasses that the viewer

wears to create a different image on each eye. The perceptual system quickly, easily, and

unconsciously turns the disparity into 3-D.

An important binocular depth cue is convergence, the inward turning of our eyes that is required

to focus on objects that are less than about 50 feet away from us. The visual cortex uses the size

of the convergence angle between the eyes to judge the object’s distance. You will be able to feel

your eyes converging if you slowly bring a finger closer to your nose while continuing to focus

on it. When you close one eye, you no longer feel the tension—convergence is a binocular depth

cue that requires both eyes to work.

The visual system also uses accommodation to help determine depth. As the lens changes its

curvature to focus on distant or close objects, information relayed from the muscles attached to

the lens helps us determine an object’s distance. Accommodation is only effective at short

viewing distances, however, so while it comes in handy when threading a needle or tying

shoelaces, it is far less effective when driving or playing sports.

Although the best cues to depth occur when both eyes work together, we are able to see depth

even with one eye closed. Monocular depth cues are depth cues that help us perceive depth using

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only one eye (Sekuler & Blake, 2006). [13]

Some of the most important are summarized in Table

4.2 "Monocular Depth Cues That Help Us Judge Depth at a Distance".

Table 4.2 Monocular Depth Cues That Help Us Judge Depth at a Distance

Name Description Example Image

Position

We tend to see objects

higher up in our field

of vision as farther

away.

The fence posts at

right appear farther

away not only

because they become

smaller but also

because they appear

higher up in the

picture.

Relative size

Assuming that the

objects in a scene are

the same size, smaller

objects are perceived

as farther away.

At right, the cars in

the distance appear

smaller than those

nearer to us.

Linear

perspective

Parallel lines appear to

converge at a distance.

We know that the

tracks at right are

parallel. When they

appear closer

together, we

determine they are

farther away.

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Name Description Example Image

Light and

shadow

The eye receives more

reflected light from

objects that are closer

to us. Normally, light

comes from above, so

darker images are in

shadow.

We see the images at

right as extending

and indented

according to their

shadowing. If we

invert the picture, the

images will reverse.

Figure 4.2

Interposition

When one object

overlaps another

object, we view it as

closer.

At right, because the

blue star covers the

pink bar, it is seen as

closer than the yellow

moon.

Aerial

perspective

Objects that appear

hazy, or that are

covered with smog or

dust, appear farther

away.

The artist who

painted the picture on

the right used aerial

perspective to make

the clouds more hazy

and thus appear

farther away.

Perceiving Motion

Many animals, including human beings, have very sophisticated perceptual skills that allow them

to coordinate their own motion with the motion of moving objects in order to create a collision

with that object. Bats and birds use this mechanism to catch up with prey, dogs use it to catch a

Frisbee, and humans use it to catch a moving football. The brain detects motion partly from the

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changing size of an image on the retina (objects that look bigger are usually closer to us) and in

part from the relative brightness of objects.

We also experience motion when objects near each other change their appearance.

The beta effect refers to the perception of motion that occurs when different images are

presented next to each other in succession (see Note 4.43 "Beta Effect and Phi Phenomenon").

The visual cortex fills in the missing part of the motion and we see the object moving. The beta

effect is used in movies to create the experience of motion. A related effect is

thephi phenomenon, in which we perceive a sensation of motion caused by the appearance and

disappearance of objects that are near each other. The phi phenomenon looks like a moving

zone or cloud of background color surrounding the flashing objects. The beta effect and the phi

phenomenon are other examples of the importance of the gestalt—our tendency to ―see more

than the sum of the parts.‖

Beta Effect and Phi Phenomenon

In the beta effect, our eyes detect motion from a series of still images, each with the object in a different place. This is

the fundamental mechanism of motion pictures (movies). In the phi phenomenon, the perception of motion is based

on the momentary hiding of an image.

Phi phenomenon:http://upload.wikimedia.org/wikipedia/commons/6/6e/Lilac-Chaser.gif

Beta effect:http://upload.wikimedia.org/wikipedia/commons/0/09/Phi_phenomenom_no_watermark.gif

K E Y T A K E A W A Y S

 Vision is the process of detecting the electromagnetic energy that surrounds us. Only a small fraction of the

electromagnetic spectrum is visible to humans.

 The visual receptor cells on the retina detect shape, color, motion, and depth.

 Light enters the eye through the transparent cornea and passes through the pupil at the center of the iris. The lens

adjusts to focus the light on the retina, where it appears upside down and backward. Receptor cells on the retina are

excited or inhibited by the light and send information to the visual cortex through the optic nerve.

 The retina has two types of photoreceptor cells: rods, which detect brightness and respond to black and white, and

cones, which respond to red, green, and blue. Color blindness occurs when people lack function in the red- or green-

sensitive cones.

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 Feature detector neurons in the visual cortex help us recognize objects, and some neurons respond selectively to

faces and other body parts.

 The Young-Helmholtz trichromatic color theory proposes that color perception is the result of the signals sent by the

three types of cones, whereas the opponent-process color theory proposes that we perceive color as three sets of

opponent colors: red-green, yellow-blue, and white-black.

 The ability to perceive depth occurs through the result of binocular and monocular depth cues.

 Motion is perceived as a function of the size and brightness of objects. The beta effect and the phi phenomenon are

examples of perceived motion.

E X E R C I S E S A N D C R I T I C A L T H I N K I N G

1. Consider some ways that the processes of visual perception help you engage in an everyday activity, such as driving a

car or riding a bicycle.

2. Imagine for a moment what your life would be like if you couldn’t see. Do you think you would be able to compensate

for your loss of sight by using other senses?

[1] Livingstone M. S. (2000). Is it warm? Is it real? Or just low spatial frequency? Science, 290, 1299.

[2] Kelsey, C.A. (1997). Detection of visual information. In W. R. Hendee & P. N. T. Wells (Eds.), The perception of

visual information (2nd ed.). New York, NY: Springer Verlag; Livingstone, M., & Hubel, D. (1998). Segregation of

form, color, movement, and depth: Anatomy, physiology, and perception. Science, 240, 740–749.

[3] Rodriguez, E., George, N., Lachaux, J.-P., Martinerie, J., Renault, B., & Varela, F. J. (1999). Perception’s shadow:

Long-distance synchronization of human brain activity. Nature, 397(6718), 430–433.

[4] Downing, P. E., Jiang, Y., Shuman, M., & Kanwisher, N. (2001). A cortical area selective for visual processing of

the human body. Science, 293(5539), 2470–2473; Haxby, J. V., Gobbini, M. I., Furey, M. L., Ishai, A., Schouten, J. L.,

& Pietrini, P. (2001). Distributed and overlapping representations of faces and objects in ventral temporal

cortex. Science, 293(5539), 2425–2430.

[5] McKone, E., Kanwisher, N., & Duchaine, B. C. (2007). Can generic expertise explain special processing for

faces? Trends in Cognitive Sciences, 11, 8–15; Pitcher, D., Walsh, V., Yovel, G., & Duchaine, B. (2007). TMS evidence

for the involvement of the right occipital face area in early face processing. Current Biology, 17, 1568–1573.

[6] Geldard, F. A. (1972). The human senses (2nd ed.). New York, NY: John Wiley & Sons.

[7] Gegenfurtner, K. R., & Kiper, D. C. (2003). Color vision. Annual Review of Neuroscience, 26, 181–206.

Saylor URL: http://www.saylor.org/books Saylor.org 35

[8] Howard, I. P., & Rogers, B. J. (2001). Seeing in depth: Basic mechanisms (Vol. 1). Toronto, Ontario, Canada:

Porteous.

[9] Witherington, D. C. (2005). The development of prospective grasping control between 5 and 7 months: A

longitudinal study. Infancy, 7(2), 143–161.

[10] Gibson, E. J., & Walk, R. D. (1960). The “visual cliff.” Scientific American, 202(4), 64–71.

[11] Campos, J. J., Langer, A., & Krowitz, A. (1970). Cardiac responses on the visual cliff in prelocomotor human

infants. Science, 170(3954), 196–197.

[12] Adolph, K. E. (2000). Specificity of learning: Why infants fall over a veritable cliff.Psychological Science, 11(4),

290–295.

[13] Sekuler, R., & Blake, R., (2006). Perception (5th ed.). New York, NY: McGraw-Hill.

4.3 Hearing L E A R N I N G O B J E C T I V E S

1. Draw a picture of the ear and label its key structures and functions, and describe the role they play in hearing.

2. Describe the process of transduction in hearing.

Like vision and all the other senses, hearing begins with transduction. Sound waves that are

collected by our ears are converted into neural impulses, which are sent to the brain where they

are integrated with past experience and interpreted as the sounds we experience. The human ear

is sensitive to a wide range of sounds, ranging from the faint tick of a clock in a nearby room to

the roar of a rock band at a nightclub, and we have the ability to detect very small variations in

sound. But the ear is particularly sensitive to sounds in the same frequency as the human voice.

A mother can pick out her child’s voice from a host of others, and when we pick up the phone

we quickly recognize a familiar voice. In a fraction of a second, our auditory system receives the

sound waves, transmits them to the auditory cortex, compares them to stored knowledge of other

voices, and identifies the identity of the caller.

The Ear

Just as the eye detects light waves, the ear detects sound waves. Vibrating objects (such as the

human vocal chords or guitar strings) cause air molecules to bump into each other and produce

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sound waves, which travel from their source as peaks and valleys much like the ripples that

expand outward when a stone is tossed into a pond. Unlike light waves, which can travel in a

vacuum, sound waves are carried within mediums such as air, water, or metal, and it is the

changes in pressure associated with these mediums that the ear detects.

As with light waves, we detect both the wavelength and the amplitude of sound waves.

The wavelength of the sound wave (known as frequency) is measured in terms of the number of

waves that arrive per second and determines our perception of pitch, the perceived frequency of a

sound. Longer sound waves have lower frequency and produce a lower pitch, whereas shorter

waves have higher frequency and a higher pitch.

The amplitude, or height of the sound wave, determines how much energy it contains and is

perceived as loudness (the degree of sound volume). Larger waves are perceived as louder.

Loudness is measured using the unit of relative loudness known as the decibel. Zero decibels

represent the absolute threshold for human hearing, below which we cannot hear a sound. Each

increase in 10 decibels represents a tenfold increase in the loudness of the sound (see Figure 4.29

"Sounds in Everyday Life"). The sound of a typical conversation (about 60 decibels) is 1,000

times louder than the sound of a faint whisper (30 decibels), whereas the sound of a jackhammer

(130 decibels) is 10 billion times louder than the whisper.

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Figure 4.29 Sounds in Everyday Life

The human ear can comfortably hear sounds up to 80 decibels. Prolonged exposure to sounds above 80 decibels can

cause hearing loss.

Audition begins in the pinna, the external and visible part of the ear, which is shaped like a

funnel to draw in sound waves and guide them into the auditory canal. At the end of the canal,

the sound waves strike the tightly stretched, highly sensitive membrane known as

thetympanic membrane (or eardrum), which vibrates with the waves. The resulting vibrations are

relayed into the middle ear through three tiny bones, known as the ossicles—the hammer (or

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malleus), anvil (or incus), and stirrup (or stapes)—to the cochlea, a snail-shaped liquid-filled

tube in the inner ear. The vibrations cause the oval window, the membrane covering the opening

of the cochlea, to vibrate, disturbing the fluid inside the cochlea.

The movements of the fluid in the cochlea bend the hair cells of the inner ear, much in the same

way that a gust of wind bends over wheat stalks in a field. The movements of the hair cells

trigger nerve impulses in the attached neurons, which are sent to the auditory nerve and then to

the auditory cortex in the brain. The cochlea contains about 16,000 hair cells, each of which

holds a bundle of fibers known as cilia on its tip. The cilia are so sensitive that they can detect a

movement that pushes them the width of a single atom. To put things in perspective, cilia

swaying at the width of an atom is equivalent to the tip of the Eiffel Tower swaying by half an

inch (Corey et al., 2004). [1]

Figure 4.30 The Human Ear

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Sound waves enter the outer ear and are transmitted through the auditory canal to the eardrum. The resulting

vibrations are moved by the three small ossicles into the cochlea, where they are detected by hair cells and sent to

the auditory nerve.

Although loudness is directly determined by the number of hair cells that are vibrating, two

different mechanisms are used to detect pitch. The frequency theory of hearing proposes

that whatever the pitch of a sound wave, nerve impulses of a corresponding frequency will be

sent to the auditory nerve. For example, a tone measuring 600 hertz will be transduced into 600

nerve impulses a second. This theory has a problem with high-pitched sounds, however, because

the neurons cannot fire fast enough. To reach the necessary speed, the neurons work together in a

sort of volley system in which different neurons fire in sequence, allowing us to detect sounds up

to about 4,000 hertz.

Not only is frequency important, but location is critical as well. The cochlea relays information

about the specific area, or place, in the cochlea that is most activated by the incoming sound.

The place theory of hearing proposes that different areas of the cochlea respond to different

frequencies. Higher tones excite areas closest to the opening of the cochlea (near the oval

window). Lower tones excite areas near the narrow tip of the cochlea, at the opposite end. Pitch

is therefore determined in part by the area of the cochlea firing the most frequently.

Just as having two eyes in slightly different positions allows us to perceive depth, so the fact that

the ears are placed on either side of the head enables us to benefit from stereophonic, or three-

dimensional, hearing. If a sound occurs on your left side, the left ear will receive the sound

slightly sooner than the right ear, and the sound it receives will be more intense, allowing you to

quickly determine the location of the sound. Although the distance between our two ears is only

about 6 inches, and sound waves travel at 750 miles an hour, the time and intensity differences

are easily detected (Middlebrooks & Green, 1991). [2]

When a sound is equidistant from both

ears, such as when it is directly in front, behind, beneath or overhead, we have more difficulty

pinpointing its location. It is for this reason that dogs (and people, too) tend to cock their heads

when trying to pinpoint a sound, so that the ears receive slightly different signals.

Hearing Loss

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More than 31 million Americans suffer from some kind of hearing impairment (Kochkin,

2005). [3]

Conductive hearing loss is caused by physical damage to the ear (such as to the

eardrums or ossicles) that reduce the ability of the ear to transfer vibrations from the outer ear to

the inner ear. Sensorineural hearing loss, which is caused by damage to the cilia or to the

auditory nerve, is less common overall but frequently occurs with age (Tennesen, 2007). [4]

The

cilia are extremely fragile, and by the time we are 65 years old, we will have lost 40% of them,

particularly those that respond to high-pitched sounds (Chisolm, Willott, & Lister, 2003). [5]

Prolonged exposure to loud sounds will eventually create sensorineural hearing loss as the cilia

are damaged by the noise. People who constantly operate noisy machinery without using

appropriate ear protection are at high risk of hearing loss, as are people who listen to loud music

on their headphones or who engage in noisy hobbies, such as hunting or motorcycling. Sounds

that are 85 decibels or more can cause damage to your hearing, particularly if you are exposed to

them repeatedly. Sounds of more than 130 decibels are dangerous even if you are exposed to

them infrequently. People who experience tinnitus (a ringing or a buzzing sensation) after being

exposed to loud sounds have very likely experienced some damage to their cilia. Taking

precautions when being exposed to loud sound is important, as cilia do not grow back.

While conductive hearing loss can often be improved through hearing aids that amplify the

sound, they are of little help to sensorineural hearing loss. But if the auditory nerve is still intact,

a cochlear implant may be used. A cochlear implant is a device made up of a series of electrodes

that are placed inside the cochlea. The device serves to bypass the hair cells by stimulating the

auditory nerve cells directly. The latest implants utilize place theory, enabling different spots on

the implant to respond to different levels of pitch. The cochlear implant can help children hear

who would normally be deaf, and if the device is implanted early enough, these children can

frequently learn to speak, often as well as normal children do (Dettman, Pinder, Briggs, Dowell,

& Leigh, 2007; Dorman & Wilson, 2004). [6]

K E Y T A K E A W A Y S

 Sound waves vibrating through mediums such as air, water, or metal are the stimulus energy that is sensed by the ear.

 The hearing system is designed to assess frequency (pitch) and amplitude (loudness).

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 Sound waves enter the outer ear (the pinna) and are sent to the eardrum via the auditory canal. The resulting

vibrations are relayed by the three ossicles, causing the oval window covering the cochlea to vibrate. The vibrations

are detected by the cilia (hair cells) and sent via the auditory nerve to the auditory cortex.

 There are two theories as to how we perceive pitch: The frequency theory of hearing suggests that as a sound wave’s

pitch changes, nerve impulses of a corresponding frequency enter the auditory nerve. The place theory of hearing

suggests that we hear different pitches because different areas of the cochlea respond to higher and lower pitches.

 Conductive hearing loss is caused by physical damage to the ear or eardrum and may be improved by hearing aids or

cochlear implants. Sensorineural hearing loss, caused by damage to the hair cells or auditory nerves in the inner ear,

may be produced by prolonged exposure to sounds of more than 85 decibels.

E X E R C I S E A N D C R I T I C A L T H I N K I N G

1. Given what you have learned about hearing in this chapter, are you engaging in any activities that might cause long-

term hearing loss? If so, how might you change your behavior to reduce the likelihood of suffering damage?

[1] Corey, D. P., García-Añoveros, J., Holt, J. R., Kwan, K. Y., Lin, S.-Y., Vollrath, M. A., Amalfitano, A.,…Zhang, D.-S. (2004). TRPA1

is a candidate for the mechano-sensitive transduction channel of vertebrate hair cells. Nature, 432, 723–730. Retrieved

fromhttp://www.nature.com/nature/journal/v432/n7018/full/nature03066.html

[2] Middlebrooks, J. C., & Green, D. M. (1991). Sound localization by human listeners.Annual Review of Psychology, 42, 135–

159.

[3] Kochkin, S. (2005). MarkeTrak VII: Hearing loss population tops 31 million people.Hearing Review, 12(7) 16–29.

[4] Tennesen, M. (2007, March 10). Gone today, hear tomorrow. New Scientist, 2594, 42–45.

[5] Chisolm, T. H., Willott, J. F., & Lister, J. J. (2003). The aging auditory system: Anatomic and physiologic changes and

implications for rehabilitation. International Journal of Audiology, 42(Suppl. 2), 2S3–2S10.

[6] Dettman, S. J., Pinder, D., Briggs, R. J. S., Dowell, R. C., & Leigh, J. R. (2007). Communication development in children who

receive the cochlear implant younger than 12 months: Risk versus benefits. Ear and Hearing, 28(2, Suppl.), 11S–18S; Dorman,

M. F., & Wilson, B. S. (2004). The design and function of cochlear implants. American Scientist, 92, 436–445.

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4.4 Tasting, Smelling, and Touching L E A R N I N G O B J E C T I V E S

1. Summarize how the senses of taste and olfaction transduce stimuli into perceptions.

2. Describe the process of transduction in the senses of touch and proprioception.

3. Outline the gate control theory of pain. Explain why pain matters and how it may be controlled.

Although vision and hearing are by far the most important, human sensation is rounded out by

four other senses, each of which provides an essential avenue to a better understanding of and

response to the world around us. These other senses are touch, taste, smell, and our sense of body

position and movement (proprioception).

Tasting

Taste is important not only because it allows us to enjoy the food we eat, but even more crucial,

because it leads us toward foods that provide energy (sugar, for instance) and away from foods

that could be harmful. Many children are picky eaters for a reason—they are biologically

predisposed to be very careful about what they eat. Together with the sense of smell, taste helps

us maintain appetite, assess potential dangers (such as the odor of a gas leak or a burning house),

and avoid eating poisonous or spoiled food.

Our ability to taste begins at the taste receptors on the tongue. The tongue detects six different

taste sensations, known respectively as sweet, salty, sour, bitter, piquancy (spicy), and umami

(savory). Umami is a meaty taste associated with meats, cheeses, soy, seaweed, and mushrooms,

and particularly found in monosodium glutamate (MSG), a popular flavor enhancer (Ikeda,

1909/2002; Sugimoto & Ninomiya, 2005). [1]

Our tongues are covered with taste buds, which are designed to sense chemicals in the mouth.

Most taste buds are located in the top outer edges of the tongue, but there are also receptors at the

back of the tongue as well as on the walls of the mouth and at the back of the throat. As we chew

food, it dissolves and enters the taste buds, triggering nerve impulses that are transmitted to the

brain (Northcutt, 2004). [2]

Human tongues are covered with 2,000 to 10,000 taste buds, and each

bud contains between 50 and 100 taste receptor cells. Taste buds are activated very quickly; a

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salty or sweet taste that touches a taste bud for even one tenth of a second will trigger a neural

impulse (Kelling & Halpern, 1983). [3]

On average, taste buds live for about 5 days, after which

new taste buds are created to replace them. As we get older, however, the rate of creation

decreases making us less sensitive to taste. This change helps explain why some foods that seem

so unpleasant in childhood are more enjoyable in adulthood.

The area of the sensory cortex that responds to taste is in a very similar location to the area that

responds to smell, a fact that helps explain why the sense of smell also contributes to our

experience of the things we eat. You may remember having had difficulty tasting food when you

had a bad cold, and if you block your nose and taste slices of raw potato, apple, and parsnip, you

will not be able to taste the differences between them. Our experience of texture in a food (the

way we feel it on our tongues) also influences how we taste it.

Smelling

As we breathe in air through our nostrils, we inhale airborne chemical molecules, which are

detected by the 10 million to 20 million receptor cells embedded in the olfactory membrane of

the upper nasal passage. The olfactory receptor cells are topped with tentacle-like protrusions

that contain receptor proteins. When an odor receptor is stimulated, the membrane sends neural

messages up the olfactory nerve to the brain (see Figure 4.31 "Smell Receptors").

Figure 4.31 Smell Receptors

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There are more than 1,000 types of odor receptor cells in the olfactory membrane.

We have approximately 1,000 types of odor receptor cells (Bensafi et al., 2004), [4]

and it is

estimated that we can detect 10,000 different odors (Malnic, Hirono, Sato, & Buck,

1999). [5]

The receptors come in many different shapes and respond selectively to different

smells. Like a lock and key, different chemical molecules ―fit‖ into different receptor cells, and

odors are detected according to their influence on a combination of receptor cells. Just as the 10

digits from 0 to 9 can combine in many different ways to produce an endless array of phone

numbers, odor molecules bind to different combinations of receptors, and these combinations are

decoded in the olfactory cortex. As you can see in Figure 4.32 "Age Differences in Smell",

women tend to have a more acute sense of smell than men. The sense of smell peaks in early

adulthood and then begins a slow decline. By ages 60 to 70, the sense of smell has become

sharply diminished.

Touching

The sense of touch is essential to human development. Infants thrive when they are cuddled and

attended to, but not if they are deprived of human contact (Baysinger, Plubell, & Harlow, 1973;

Feldman, 2007; Haradon, Bascom, Dragomir, & Scripcaru, 1994). [6]

Touch communicates

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warmth, caring, and support, and is an essential part of the enjoyment we gain from our social

interactions with close others (Field et al., 1997; Kelter, 2009). [7]

The skin, the largest organ in the body, is the sensory organ for touch. The skin contains a

variety of nerve endings, combinations of which respond to particular types of pressures and

temperatures. When you touch different parts of the body, you will find that some areas are more

ticklish, whereas other areas respond more to pain, cold, or heat.

The thousands of nerve endings in the skin respond to four basic sensations:Pressure, hot, cold,

and pain, but only the sensation of pressure has its own specialized receptors. Other sensations

are created by a combination of the other four. For instance:

The experience of a tickle is caused by the stimulation of neighboring pressure receptors.

The experience of heat is caused by the stimulation of hot and cold receptors.

The experience of itching is caused by repeated stimulation of pain receptors.

The experience of wetness is caused by repeated stimulation of cold and pressure receptors.

The skin is important not only in providing information about touch and temperature but also

in proprioception—the ability to sense the position and movement of our body parts.

Proprioception is accomplished by specialized neurons located in the skin, joints, bones, ears,

and tendons, which send messages about the compression and the contraction of muscles

throughout the body. Without this feedback from our bones and muscles, we would be unable to

play sports, walk, or even stand upright.

The ability to keep track of where the body is moving is also provided by thevestibular system, a

set of liquid-filled areas in the inner ear that monitors the head’s position and movement,

maintaining the body’s balance. As you can see in Figure 4.33 "The Vestibular System", the

vestibular system includes the semicircular canals and the vestibular sacs. These sacs connect

the canals with the cochlea. The semicircular canals sense the rotational movements of the body

and the vestibular sacs sense linear accelerations. The vestibular system sends signals to the

neural structures that control eye movement and to the muscles that keep the body upright.

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Figure 4.33 The Vestibular System

The vestibular system includes the semicircular canals (brown) that transduce the rotational movements of the

body and the vestibular sacs (blue) that sense linear accelerations.

Experiencing Pain

We do not enjoy it, but the experience of pain is how the body informs us that we are in danger.

The burn when we touch a hot radiator and the sharp stab when we step on a nail lead us to

change our behavior, preventing further damage to our bodies. People who cannot experience

pain are in serious danger of damage from wounds that others with pain would quickly notice

and attend to.

The gate control theory of pain proposes that pain is determined by the operation of two types of

nerve fibers in the spinal cord. One set of smaller nerve fibers carries pain from the body to the

brain, whereas a second set of larger fibers is designed to stop or start (as a gate would) the flow

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of pain (Melzack & Wall, 1996). [8]

It is for this reason that massaging an area where you feel

pain may help alleviate it—the massage activates the large nerve fibers that block the pain

signals of the small nerve fibers (Wall, 2000). [9]

Experiencing pain is a lot more complicated than simply responding to neural messages,

however. It is also a matter of perception. We feel pain less when we are busy focusing on a

challenging activity (Bantick, Wise, Ploghaus, Clare, Smith, & Tracey, 2002), [10]

which can help

explain why sports players may feel their injuries only after the game. We also feel less pain

when we are distracted by humor (Zweyer, Velker, & Ruch, 2004). [11]

And pain is soothed by

the brain’s release of endorphins, natural hormonal pain killers. The release of endorphins can

explain the euphoria experienced in the running of a marathon (Sternberg, Bailin, Grant, &

Gracely, 1998). [12]

K E Y T A K E A W A Y S

 The ability to taste, smell, and touch are important because they help us avoid harm from environmental toxins.

 The many taste buds on our tongues and inside our mouths allow us to detect six basic taste sensations: sweet, salty,

sour, bitter, piquancy, and umami.

 In olfaction, transduction occurs as airborne chemicals that are inhaled through the nostrils are detected by receptors

in the olfactory membrane. Different chemical molecules fit into different receptor cells, creating different smells.

 On average, women have a better sense of smell than men, and the ability to smell diminishes with age.

 We have a range of different nerve endings embedded in the skin, combinations of which respond to the four basic

sensations of pressure, hot, cold, and pain. But only the sensation of pressure has its own specialized receptors.

 Proprioception is our ability to sense the positions and movements of our body parts. Postural and movement

information is detected by special neurons located in the skin, joints, bones, ears, and tendons, which pick up

messages from the compression and the contraction of muscles throughout the body.

 The vestibular system, composed of structures in the inner ear, monitors the head’s position and movement,

maintaining the body’s balance.

 Gate control theory explains how large and small neurons work together to transmit and regulate the flow of pain to

the brain.

E X E R C I S E S A N D C R I T I C A L T H I N K I N G

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1. Think of the foods that you like to eat the most. Which of the six taste sensations do these foods have, and why do

you think that you like these particular flavors?

2. Why do you think that women might have a better developed sense of smell than do men?

3. Why is experiencing pain a benefit for human beings?

[1] Ikeda, K. (2002). [New seasonings]. Chemical Senses, 27(9), 847–849. Translated andshortened to 75% by Y. Ogiwara & Y.

Ninomiya from the Journal of the Chemical Society of Tokyo, 30, 820–836. (Original work published 1909); Sugimoto, K., &

Ninomiya, Y. (2005). Introductory remarks on umami research: Candidate receptors and signal transduction mechanisms on

umami. Chemical Senses, 30(Suppl. 1), Pi21–i22.

[2] Northcutt, R. G. (2004). Taste buds: Development and evolution. Brain, Behavior and Evolution, 64(3), 198–206.

[3] Kelling, S. T., & Halpern, B. P. (1983). Taste flashes: Reaction times, intensity, and quality. Science, 219, 412–414.

[4] Bensafi, M., Zelano, C., Johnson, B., Mainland, J., Kahn, R., & Sobel, N. (2004). Olfaction: From sniff to percept. In M. S.

Gazzaniga (Ed.), The cognitive neurosciences (3rd ed.). Cambridge, MA: MIT Press.

[5] Malnic, B., Hirono, J., Sato, T., & Buck, L. B. (1999). Combinatorial receptor codes for odors. Cell, 96, 713–723.

[6] Baysinger, C. M., Plubell, P. E., & Harlow, H. F. (1973). A variable-temperature surrogate mother for studying attachment in

infant monkeys. Behavior Research Methods & Instrumentation, 5(3), 269–272; Feldman, R. (2007). Maternal-infant contact and

child development: Insights from the kangaroo intervention. In L. L’Abate (Ed.), Low-cost approaches to promote physical and

mental health: Theory, research, and practice (pp. 323–351). New York, NY: Springer Science + Business Media; Haradon, G.,

Bascom, B., Dragomir, C., & Scripcaru, V. (1994). Sensory functions of institutionalized Romanian infants: A pilot

study. Occupational Therapy International, 1(4), 250–260.

[7] Field, T., Lasko, D., Mundy, P., Henteleff, T., Kabat, S., Talpins, S., & Dowling, M. (1997). Brief report: Autistic children’s

attentiveness and responsivity improve after touch therapy. Journal of Autism and Developmental Disorders, 27(3), 333–338;

Keltner, D. (2009).Born to be good: The science of a meaningful life. New York, NY: Norton.

[8] Melzack, R., & Wall, P. (1996). The challenge of pain. London, England: Penguin.

[9] Wall, P. (2000). Pain: The science of suffering. New York, NY: Columbia University Press.

[10] Bantick, S. J., Wise, R. G., Ploghaus, A., Clare, S., Smith, S. M., & Tracey, I. (2002). Imaging how attention modulates pain in

humans using functional MRI. Brain: A Journal of Neurology, 125(2), 310–319.

[11] Zweyer, K., Velker, B., & Ruch, W. (2004). Do cheerfulness, exhilaration, and humor production moderate pain tolerance? A

FACS study. Humor: International Journal of Humor Research, 17(1-2), 85–119.

Saylor URL: http://www.saylor.org/books Saylor.org 49

[12] Sternberg, W. F., Bailin, D., Grant, M., & Gracely, R. H. (1998). Competition alters the perception of noxious stimuli in male

and female athletes. Pain, 76(1–2), 231–238.

4.5 Accuracy and Inaccuracy in Perception L E A R N I N G O B J E C T I V E S

1. Describe how sensation and perception work together through sensory interaction, selective attention, sensory

adaptation, and perceptual constancy.

2. Give examples of how our expectations may influence our perception, resulting in illusions and potentially inaccurate

judgments.

The eyes, ears, nose, tongue, and skin sense the world around us, and in some cases perform

preliminary information processing on the incoming data. But by and large, we do not experience

sensation—we experience the outcome of perception—the total package that the brain puts

together from the pieces it receives through our senses and that the brain creates for us to

experience. When we look out the window at a view of the countryside, or when we look at the

face of a good friend, we don’t just see a jumble of colors and shapes—we see, instead, an image

of a countryside or an image of a friend (Goodale & Milner, 2006). [1]

How the Perceptual System Interprets the Environment

This meaning-making involves the automatic operation of a variety of essential perceptual

processes. One of these is sensory interaction—the working together of different senses to create

experience. Sensory interaction is involved when taste, smell, and texture combine to create the

flavor we experience in food. It is also involved when we enjoy a movie because of the way the

images and the music work together.

Although you might think that we understand speech only through our sense of hearing, it turns

out that the visual aspect of speech is also important. One example of sensory interaction is

shown in the McGurk effect—an error in perception that occurs when we misperceive sounds

because the audio and visual parts of the speech are mismatched. You can witness the effect

yourself by viewing Note 4.69 "Video Clip: The McGurk Effect".

Video Clip: The McGurk Effect

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The McGurk effect is an error in sound perception that occurs when there is a mismatch between the senses of hearing and

seeing. You can experience it here.

Other examples of sensory interaction include the experience of nausea that can occur when the

sensory information being received from the eyes and the body does not match information from

the vestibular system (Flanagan, May, & Dobie, 2004) [2]

and synesthesia—an experience in

which one sensation (e.g., hearing a sound) creates experiences in another (e.g., vision). Most

people do not experience synesthesia, but those who do link their perceptions in unusual ways,

for instance, by experiencing color when they taste a particular food or by hearing sounds when

they see certain objects (Ramachandran, Hubbard, Robertson, & Sagiv, 2005). [3]

Another important perceptual process is selective attention—the ability to focus on some sensory

inputs while tuning out others. View Note 4.71 "Video Clip: Selective Attention" and count the

number of times the people playing with the ball pass it to each other. You may find that, like

many other people who view it for the first time, you miss something important because you

selectively attend to only one aspect of the video (Simons & Chabris, 1999). [4]

Perhaps the

process of selective attention can help you see why the security guards completely missed the

fact that the Chaser group’s motorcade was a fake—they focused on some aspects of the

situation, such as the color of the cars and the fact that they were there at all, and completely

ignored others (the details of the security information).

Video Clip: Selective Attention

Watch this video and carefully count how many times the people pass the ball to each other.

Selective attention also allows us to focus on a single talker at a party while ignoring other

conversations that are occurring around us (Broadbent, 1958; Cherry, 1953). [5]

Without this

automatic selective attention, we’d be unable to focus on the single conversation we want to

hear. But selective attention is not complete; we also at the same time monitor what’s happening

in the channels we are not focusing on. Perhaps you have had the experience of being at a party

and talking to someone in one part of the room, when suddenly you hear your name being

mentioned by someone in another part of the room. This cocktail party phenomenon shows us

that although selective attention is limiting what we processes, we are nevertheless at the same

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time doing a lot of unconscious monitoring of the world around us—you didn’t know you were

attending to the background sounds of the party, but evidently you were.

A second fundamental process of perception is sensory adaptation—a decreased sensitivity to a

stimulus after prolonged and constant exposure. When you step into a swimming pool, the water

initially feels cold, but after a while you stop noticing it. After prolonged exposure to the same

stimulus, our sensitivity toward it diminishes and we no longer perceive it. The ability to adapt to

the things that don’t change around us is essential to our survival, as it leaves our sensory

receptors free to detect the important and informative changes in our environment and to respond

accordingly. We ignore the sounds that our car makes every day, which leaves us free to pay

attention to the sounds that are different from normal, and thus likely to need our attention. Our

sensory receptors are alert to novelty and are fatigued after constant exposure to the same

stimulus.

If sensory adaptation occurs with all senses, why doesn’t an image fade away after we stare at it

for a period of time? The answer is that, although we are not aware of it, our eyes are constantly

flitting from one angle to the next, making thousands of tiny movements (called saccades) every

minute. This constant eye movement guarantees that the image we are viewing always falls on

fresh receptor cells. What would happen if we could stop the movement of our eyes?

Psychologists have devised a way of testing the sensory adaptation of the eye by attaching an

instrument that ensures a constant image is maintained on the eye’s inner surface. Participants

are fitted with a contact lens that has miniature slide projector attached to it. Because the

projector follows the exact movements of the eye, the same image is always projected,

stimulating the same spot, on the retina. Within a few seconds, interesting things begin to

happen. The image will begin to vanish, then reappear, only to disappear again, either in pieces

or as a whole. Even the eye experiences sensory adaptation (Yarbus, 1967). [6]

One of the major problems in perception is to ensure that we always perceive the same object in

the same way, despite the fact that the sensations that it creates on our receptors changes

dramatically. The ability to perceive a stimulus as constant despite changes in sensation is

known asperceptual constancy. Consider our image of a door as it swings. When it is closed, we

see it as rectangular, but when it is open, we see only its edge and it appears as a line. But we

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never perceive the door as changing shape as it swings—perceptual mechanisms take care of the

problem for us by allowing us to see a constant shape.

The visual system also corrects for color constancy. Imagine that you are wearing blue jeans and

a bright white t-shirt. When you are outdoors, both colors will be at their brightest, but you will

still perceive the white t-shirt as bright and the blue jeans as darker. When you go indoors, the

light shining on the clothes will be significantly dimmer, but you will still perceive the t-shirt as

bright. This is because we put colors in context and see that, compared to its surroundings, the

white t-shirt reflects the most light (McCann, 1992). [7]

In the same way, a green leaf on a cloudy

day may reflect the same wavelength of light as a brown tree branch does on a sunny day.

Nevertheless, we still perceive the leaf as green and the branch as brown.

Illusions

Although our perception is very accurate, it is not perfect. Illusions occur when the perceptual

processes that normally help us correctly perceive the world around us are fooled by a

particular situation so that we see something that does not exist or that is incorrect. Figure 4.34

"Optical Illusions as a Result of Brightness Constancy (Left) and Color Constancy

(Right)" presents two situations in which our normally accurate perceptions of visual constancy

have been fooled.

Figure 4.34 Optical Illusions as a Result of Brightness Constancy (Left) and Color Constancy (Right)

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Look carefully at the snakelike pattern on the left. Are the green strips really brighter than the background? Cover

the white curves and you’ll see they are not. Square A in the right-hand image looks very different from square B,

even though they are exactly the same.

Source: Right image courtesy of Edward H.

Adelson,http://commons.wikimedia.org/wiki/File:Grey_square_optical_illusion.PNG.

Another well-known illusion is the Mueller-Lyer illusion (see Figure 4.35 "The Mueller-Lyre

Illusion"). The line segment in the bottom arrow looks longer to us than the one on the top, even

though they are both actually the same length. It is likely that the illusion is, in part, the result of

the failure of monocular depth cues—the bottom line looks like an edge that is normally farther

away from us, whereas the top one looks like an edge that is normally closer.

Figure 4.35 The Mueller-Lyre Illusion

The Mueller-Lyre illusion makes the line segment at the top of the left picture appear shorter than the one at the

bottom. The illusion is caused, in part, by the monocular distance cue of depth—the bottom line looks like an edge

that is normally farther away from us, whereas the top one looks like an edge that is normally closer.

The moon illusion refers to the fact that the moon is perceived to be about 50% larger when it is

near the horizon than when it is seen overhead, despite the fact that both moons are the same size

and cast the same size retinal image. The monocular depth cues of position and aerial perspective

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(see Figure 4.36 "The Moon Illusion") create the illusion that things that are lower and more

hazy are farther away. The skyline of the horizon (trees, clouds, outlines of buildings) also gives

a cue that the moon is far away, compared to a moon at its zenith. If we look at a horizon moon

through a tube of rolled up paper, taking away the surrounding horizon cues, the moon will

immediately appear smaller.

The Ponzo illusion operates on the same principle. As you can see in Figure 4.37 "The Ponzo

Illusion", the top yellow bar seems longer than the bottom one, but if you measure them you’ll

see that they are exactly the same length. The monocular depth cue of linear perspective leads us

to believe that, given two similar objects, the distant one can only cast the same size retinal

image as the closer object if it is larger. The topmost bar therefore appears longer.

Figure 4.37 The Ponzo Illusion

The Ponzo illusion is caused by a failure of the monocular depth cue of linear perspective: Both bars are the same

size even though the top one looks larger.

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Illusions demonstrate that our perception of the world around us may be influenced by our prior

knowledge. But the fact that some illusions exist in some cases does not mean that the perceptual

system is generally inaccurate—in fact, humans normally become so closely in touch with their

environment that that the physical body and the particular environment that we sense and

perceive becomes embodied—that is, built into and linked with—our cognition, such that the

worlds around us become part of our brain (Calvo & Gamila, 2008). [8]

The close relationship

between people and their environments means that, although illusions can be created in the lab

and under some unique situations, they may be less common with active observers in the real

world (Runeson, 1988). [9]

The Important Role of Expectations in Perception

Our emotions, mind-set, expectations, and the contexts in which our sensations occur all have a

profound influence on perception. People who are warned that they are about to taste something

bad rate what they do taste more negatively than people who are told that the taste won’t be so

bad (Nitschke et al., 2006), [10]

and people perceive a child and adult pair as looking more alike

when they are told that they are parent and child (Bressan & Dal Martello, 2002). [11]

Similarly,

participants who see images of the same baby rate it as stronger and bigger when they are told it

is a boy as opposed to when they are told it is a girl (Stern & Karraker, 1989), [12]

and research

participants who learn that a child is from a lower-class background perceive the child’s scores

on an intelligence test as lower than people who see the same test taken by a child they are told is

from an upper-class background (Darley & Gross, 1983). [13]

Plassmann, O’Doherty, Shiv, and

Rangel (2008) [14]

found that wines were rated more positively and caused greater brain activity

in brain areas associated with pleasure when they were said to cost more than when they were

said to cost less. And even experts can be fooled: Professional referees tended to assign more

penalty cards to soccer teams for videotaped fouls when they were told that the team had a

history of aggressive behavior than when they had no such expectation (Jones, Paull, & Erskine,

2002). [15]

Our perceptions are also influenced by our desires and motivations. When we are hungry, food-

related words tend to grab our attention more than non-food-related words (Mogg, Bradley,

Hyare, & Lee, 1998), [16]

we perceive objects that we can reach as bigger than those that we

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cannot reach (Witt & Proffitt, 2005), [17]

and people who favor a political candidate’s policies

view the candidate’s skin color more positively than do those who oppose the candidate’s

policies (Caruso, Mead, & Balcetis, 2009). [18]

Even our culture influences perception. Chua,

Boland, and Nisbett (2005) [19]

showed American and Asian graduate students different images,

such as an airplane, an animal, or a train, against complex backgrounds. They found that

(consistent with their overall individualistic orientation) the American students tended to focus

more on the foreground image, while Asian students (consistent with their interdependent

orientation) paid more attention to the image’s context. Furthermore, Asian-American students

focused more or less on the context depending on whether their Asian or their American identity

had been activated.

Psychology in Everyday Life: How Understanding Sensation and Perception Can Save Lives

Human factors is the field of psychology that uses psychological knowledge, including the principles of sensation and

perception, to improve the development of technology. Human factors has worked on a variety of projects, ranging

from nuclear reactor control centers and airplane cockpits to cell phones and websites (Proctor & Van Zandt,

2008). [20]

For instance, modern televisions and computer monitors were developed on the basis of the trichromatic

color theory, using three color elements placed close enough together so that the colors are blended by the eye.

Knowledge of the visual system also helped engineers create new kinds of displays, such as those used on notebook

computers and music players, and better understand how using cell phones while driving may contribute to

automobile accidents (Lee & Strayer, 2004). [21]

Human factors also has made substantial contributions to airline safety. About two thirds of accidents on commercial

airplane flights are caused by human error (Nickerson, 1998). [22]

During takeoff, travel, and landing, the pilot

simultaneously communicates with ground control, maneuvers the plane, scans the horizon for other aircraft, and

operates controls. The need for a useable interface that works easily and naturally with the pilot’s visual perception is

essential.

Psychologist Conrad Kraft (1978) [23]

hypothesized that as planes land, with no other distance cues visible, pilots may

be subjected to a type of moon illusion, in which the city lights beyond the runway appear much larger on the retina

than they really are, deceiving the pilot into landing too early. Kraft’s findings caused airlines to institute new flight

safety measures, where copilots must call out the altitude progressively during the descent, which has probably

decreased the number of landing accidents.

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Figure 4.38 presents the design of an airplane instrument panel before and after it was redesigned by human factors

psychologists. On the left is the initial design in which the controls were crowded and cluttered, in no logical

sequence, each control performing one task. The controls were more or less the same in color, and the gauges were

not easy to read. The redesigned digital cockpit (right on Figure 4.38) shows a marked improvement in usability.

More of the controls are color-coded and multifunctional so that there is less clutter on the dashboard. Screens make

use of LCD and 3-D graphics. Text sizes are changeable—increasing readability—and many of the functions have

become automated, freeing up the pilots concentration for more important activities.

Figure 4.38

One important aspect of the redesign was based on the principles of sensory adaptation. Displays that are easy to see

in darker conditions quickly become unreadable when the sun shines directly on them. It takes the pilot a relatively

long time to adapt to the suddenly much brighter display. Furthermore, perceptual contrast is important. The display

cannot be so bright at night that the pilot is unable to see targets in the sky or on the land. Human factors

psychologists used these principles to determine the appropriate stimulus intensity needed on these displays so that

pilots would be able to read them accurately and quickly under a wide range of conditions. The psychologists

accomplished this by developing an automatic control mechanism that senses the ambient light visible through the

front cockpit windows and that detects the light falling on the display surface, and then automatically adjusts the

intensity of the display for the pilot (Silverstein, Krantz, Gomer, Yeh, & Monty, 1990; Silverstein & Merrifield,

1985). [24]

K E Y T A K E A W A Y S

 Sensory interaction occurs when different senses work together, for instance, when taste, smell, and touch together

produce the flavor of food.

 Selective attention allows us to focus on some sensory experiences while tuning out others.

 Sensory adaptation occurs when we become less sensitive to some aspects of our environment, freeing us to focus on

more important changes.

 Perceptual constancy allows us to perceive an object as the same, despite changes in sensation.

 Cognitive illusions are examples of how our expectations can influence our perceptions.

 Our emotions, motivations, desires, and even our culture can influence our perceptions.

E X E R C I S E S A N D C R I T I C A L T H I N K I N G

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1. Consider the role of the security personnel at the APEC meeting who let the Chaser group’s car enter the security

area. List some perceptual processes that might have been at play.

2. Consider some cases where your expectations about what you think you might be going to experience have

influenced your perceptions of what you actually experienced.

[1] Goodale, M., & Milner, D. (2006). One brain—Two visual systems. Psychologist, 19(11), 660–663.

[2] Flanagan, M. B., May, J. G., & Dobie, T. G. (2004). The role of vection, eye movements, and postural instability in the etiology

of motion sickness. Journal of Vestibular Research: Equilibrium and Orientation, 14(4), 335–346.

[3] Ramachandran, V. S., Hubbard, E. M., Robertson, L. C., & Sagiv, N. (2005). The emergence of the human mind: Some clues

from synesthesia. In Synesthesia: Perspectives From Cognitive Neuroscience (pp. 147–190). New York, NY: Oxford University

Press.

[4] Simons, D. J., & Chabris, C. F. (1999). Gorillas in our midst: Sustained inattentional blindness for dynamic events. Perception,

28(9), 1059–1074.

[5] Broadbent, D. E. (1958). Perception and communication. New York, NY: Pergamon; Cherry, E. C. (1953). Some experiments

on the recognition of speech, with one and with two ears. Journal of the Acoustical Society of America, 25, 975–979.

[6] Yarbus, A. L. (1967). Eye movements and vision. New York, NY: Plenum Press.

[7] McCann, J. J. (1992). Rules for color constancy. Ophthalmic and Physiologic Optics, 12(2), 175–177.

[8] Calvo, P., & Gomila, T. (Eds.). (2008). Handbook of cognitive science: An embodied approach. San Diego, CA: Elsevier.

[9] Runeson, S. (1988). The distorted room illusion, equivalent configurations, and the specificity of static optic arrays. Journal

of Experimental Psychology: Human Perception and Performance, 14(2), 295–304.

[10] Nitschke, J. B., Dixon, G. E., Sarinopoulos, I., Short, S. J., Cohen, J. D., Smith, E. E.,…Davidson, R. J. (2006). Altering

expectancy dampens neural response to aversive taste in primary taste cortex. Nature Neuroscience 9, 435–442.

[11] Bressan, P., & Dal Martello, M. F. (2002). Talis pater, talis filius: Perceived resemblance and the belief in genetic

relatedness. Psychological Science, 13, 213–218.

[12] Stern, M., & Karraker, K. H. (1989). Sex stereotyping of infants: A review of gender labeling studies. Sex Roles, 20(9–10),

501–522.

[13] Darley, J. M., & Gross, P. H. (1983). A hypothesis-confirming bias in labeling effects.Journal of Personality and Social

Psychology, 44, 20–33.

[14] Plassmann, H., O’Doherty, J., Shiv, B., & Rangel, A. (2008). Marketing actions can moderate neural representations of

experienced pleasantness. Proceedings of the National Academy of Sciences, 105(3), 1050–1054.

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[15] Jones, M. V., Paull, G. C., & Erskine, J. (2002). The impact of a team’s aggressive reputation on the decisions of association

football referees. Journal of Sports Sciences, 20, 991–1000.

[16] Mogg, K., Bradley, B. P., Hyare, H., & Lee, S. (1998). Selective attention to food related stimuli in hunger. Behavior Research

& Therapy, 36(2), 227–237.

[17] Witt, J. K., & Proffitt, D. R. (2005). See the ball, hit the ball: Apparent ball size is correlated with batting

average. Psychological Science, 16(12), 937–938.

[18] Caruso, E. M., Mead, N. L., & Balcetis, E. (2009). Political partisanship influences perception of biracial candidates’ skin

tone. PNAS Proceedings of the National Academy of Sciences of the United States of America, 106(48), 20168–20173.

[19] Chua, H. F., Boland, J. E., & Nisbett, R. E. (2005). Cultural variation in eye movements during scene perception. Proceedings

of the National Academy of Sciences, 102, 12629–12633.

[20] Proctor, R. W., & Van Zandt, T. (2008). Human factors in simple and complex systems (2nd ed.). Boca Raton, FL: CRC Press.

[21] Lee, J., & Strayer, D. (2004). Preface to the special section on driver distraction.Human Factors, 46(4), 583.

[22] Nickerson, R. S. (1998). Applied experimental psychology. Applied Psychology: An International Review, 47, 155–173.

[23] Kraft, C. (1978). A psychophysical approach to air safety: Simulator studies of visual illusions in night approaches. In H. L.

Pick, H. W. Leibowitz, J. E. Singer, A. Steinschneider, & H. W. Steenson (Eds.), Psychology: From research to practice. New York,

NY: Plenum Press.

[24] Silverstein, L. D., Krantz, J. H., Gomer, F. E., Yeh, Y., & Monty, R. W. (1990). The effects of spatial sampling and luminance

quantization on the image quality of color matrix displays. Journal of the Optical Society of America, Part A, 7, 1955–1968;

Silverstein, L. D., & Merrifield, R. M. (1985). The development and evaluation of color systems for airborne applications: Phase I

Fundamental visual, perceptual, and display systems considerations(Tech. Report DOT/FAA/PM085019). Washington, DC:

Federal Aviation Administration.

4.6 Chapter Summary

Sensation and perception work seamlessly together to allow us to detect both the presence of,

and changes in, the stimuli around us.

The study of sensation and perception is exceedingly important for our everyday lives because

the knowledge generated by psychologists is used in so many ways to help so many people.

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Each sense accomplishes the basic process of transduction—the conversion of stimuli detected

by receptor cells into electrical impulses that are then transported to the brain—in different, but

related, ways.

Psychophysics is the branch of psychology that studies the effects of physical stimuli on sensory

perceptions. Psychophysicists study the absolute threshold of sensation as well as the difference

threshold, or just noticeable difference (JND). Weber’s law maintains that the JND of a stimulus

is a constant proportion of the original intensity of the stimulus.

Most of our cerebral cortex is devoted to seeing, and we have substantial visual skills. The eye is

a specialized system that includes the cornea, pupil, iris, lens, and retina. Neurons, including rods

and cones, react to light landing on the retina and send it to the visual cortex via the optic nerve.

Images are perceived, in part, through the action of feature detector neurons.

The shade of a color, known as hue, is conveyed by the wavelength of the light that enters the

eye. The Young-Helmholtz trichromatic color theory and the opponent-process color theory are

theories of how the brain perceives color.

Depth is perceived using both binocular and monocular depth cues. Monocular depth cues are

based on gestalt principles. The beta effect and the phi phenomenon are important in detecting

motion.

The ear detects both the amplitude (loudness) and frequency (pitch) of sound waves.

Important structures of the ear include the pinna, eardrum, ossicles, cochlea, and the oval

window.

The frequency theory of hearing proposes that as the pitch of a sound wave increases, nerve

impulses of a corresponding frequency are sent to the auditory nerve. The place theory of hearing

proposes that different areas of the cochlea respond to different frequencies.

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Sounds that are 85 decibels or more can cause damage to your hearing, particularly if you are

exposed to them repeatedly. Sounds that exceed 130 decibels are dangerous, even if you are

exposed to them infrequently.

The tongue detects six different taste sensations, known respectively as sweet, salty, sour, bitter,

piquancy (spicy), and umami (savory).

We have approximately 1,000 types of odor receptor cells and it is estimated that we can detect

10,000 different odors.

Thousands of nerve endings in the skin respond to four basic sensations: Pressure, hot, cold, and

pain, but only the sensation of pressure has its own specialized receptors. The ability to keep

track of where the body is moving is provided by the vestibular system.

Perception involves the processes of sensory interaction, selective attention, sensory adaptation,

and perceptual constancy.

Although our perception is very accurate, it is not perfect. Our expectations and emotions color

our perceptions and may result in illusions.