Perception

 

John G. Taylor (1999) describes perception as the process of bringing in one or two stimulus events and then constructing they rest of the stimulus events from our knowledge of the environment.  This implies that one of the functions of the brain is to learn an environment and how to respond to it. Remember, we did not evolve to live in our current environment but to live 150,000 years ago. Therefore any explanation of perception must explain perception 150,000 years ago, not perception today.

 

Understanding Sensation and Perception

The brain integrates and reacts to incoming information, including that of light, sound, and pressure. Sensation is the process by which this energy is transformed into neural activity. Thus, our sense organs let the physical world speak to the nervous system in biological terms (Coren, Porac, & Ward, 1984). Perception is the process by which we organize and interpret sensory information.

 

Types of Sensory Systems

In this chapter we are going to cover two-types of sensory systems. The first type is the so called “major” systems or more accurately, the latest to evolve. The second type systems we will cover are the “minor” or the earliest to evolve.  The major systems are vision and hearing. The minor systems are smell, taste, and touch. The first systems to be covered are vision and hearing. These systems evolved recently and processing in the brain of these two systems is essentially the same. The big difference between the major and minor sensory systems is that the minor systems are generally “hard wired”. That is they function very well from birth on and do not require any interaction with the environment. The major systems have “critical periods” within which they require stimulation in order to function properly, if the stimulation is not received, then perception is distorted.

 

S.B. and Vision

When S.B. was born, his eyes were insensitive to light. An operation made this sensitivity possible. Initially, he had sensations, in that neural activity was stimulated by light. But he had no perception (Gregory, 1966). Until age 52, S.B. was unable to see at all. He was, however, active and fearless in his approach to the world: He bicycled; he built things; he always tried to imagine how the objects he touched might look.

 

At 52, S.B. underwent a corneal graft, an operation that enabled him to see for the first time in his life. Initially, he saw only blurs; objects did not take form. But in a few days, he was able to see objects as discrete shapes. Soon he had little difficulty recognizing objects by sight, as long as these were items he had previously touched. For example, he could readily tell time because while blind he had developed the habit of carrying a pocket watch with no crystal; he would feel where the hands were.

 

Other visual tasks proved more difficult. S.B. had considerable trouble perceiving distance--looking down from a window some 30 or 40 feet above the ground, he thought he could lower himself down by his hands. He never learned to read by sight, although he almost immediately recognized capital letters and numbers. Again, the crucial factor seemed to be his previous experience touching these symbols: In the school for the blind that he had attended, prior to learning Braille, he had learned to recognize by touch the shapes of capital letters and numbers.

 

You might think that S.B. was ecstatic about his new eyesight, but this was not the case. Shortly after the operation, he became depressed and less active, and he stayed this way until his death three years later. Depression can be a common reaction among those who gain sight as adults, perhaps because they realize what they have previously missed or perhaps because their new vision does not function optimally (Gazzaniga, 1992). In any event, following their operation some individuals--including S.B.--revert to living in the dark.

 

Types of Processing

We perceive the world using processes. First we learn how to understand what it is we perceive using bottom-up processing. After we have learned what is in the environment and how to perceive it, we switch to top-down processing. We start our using bottom-up processing because it is slow and laborious however it is great at teaching us what we perceive. We then switch to top-down processing because it is fast and it helps us navigate the world quickly.

 

Bottom-up processing happens when we first start to learn the environment. We take in the stimulus and break it down into its basic components. After each component is analyzed, the image is put back together so that we may perceive it as a whole. Bottom-up processing is very accurate but is very slow. It is great for learning an environment, how it operates, and what is in it. Below is a diagram of bottom-up processing:

 

 

After we learn to perceive and understand the environment we switch to top-down processing. Top-down processing involves the brain telling the sensory system what it expects to see and therefore that is what we see. Top-down processing is very fast, but can be very inaccurate.

 

Cells that respond only to specific environmental characteristics like the orientation of lines are called feature detectors, and their function seems to have a “critical period” for development. In other words, stimulation of these cells must occur within a certain time frame of that function is either totally or partially lost forever. Consider again the example of S.B. In one instance, he was shown a woodworking tool in a glass case at a museum. He did not understand what he saw. Then it was taken out of the case. S.B. closed his eyes, touched it, and then exclaimed, "Now I can see!"  Another example is an infant born with cataracts. If the cataracts are not removed within the first 3 months, the child will never be able to distinguish between a sphere and a cube.

 

All of our senses share certain characteristics. Each is stimulated by external energy that produces neural impulses in receptor neurons, in a process known as transduction. These neural impulses give rise to different sensations that are coordinated into perception. Granted that all sensations arrive at the brain via a neural route, and granted that the neurons involved are anatomically identical, what explains the variety of sensations we eventually experience? One answer was proposed by Johannes Müller (1826, 1826b) in his doctrine of specific nerve energies. According to this view, neural messages register as different sensations because they move along specific nerves that terminate in given areas of the brain. The doctrine of specific nerve energies explains, for instance, why we can distinguish sound from odor: Nerves leading from the ears and the nose end in parts of the brain which learn to hear and respond to smells.  

 

This theory can also explain aspects of an unusual sensory phenomenon known as synesthesia, in which stimulation of one type of sensory receptor gives rise to the involuntary experience of another sense (Andrews, 1978; Cytowic & Wood, 1982; Marks, 1975). Here the individual tastes a sound, hears a color, or sees a smell. Synesthesia is not well understood, but some theorists suggest that it is due to unusual connections among neurons (Motluk, 1994).

 

A further explanation is needed, and one popular hypothesis is that the overall pattern of neural excitation and inhibition in the brain produces the specificity of sensations (Kandel, 1981). Synesthesia, from this perspective, is the result of a complex integration of neural messages, perhaps in terms of their emotional associations (Cytowic, 1989). Just where in the brain this integration occurs is unknown, as is exactly how it takes place.

 

Adaptation-Level Theory

Fechner addressed the relationship between stimulus intensity and sensation intensity without reference to context. His focus was only on the stimuli being judged. The stimulus being judged influences magnitude estimates, but adaptation-level theory proposes that scaling is additionally affected by other stimuli surrounding the stimulus being judged. Also critical are residual stimuli, those that have been experienced in the past (Helson, 1964).

 

Background stimuli and residual stimuli create the context or adaptation level, in which scaling occurs. Height is a typical example. We judge people as short or tall not only in terms of their actual heights, but also in terms of other people in the vicinity and in terms of other people we have known. A common experience is to see National Basketball Association point guards like Allen Iverson and Jason Williams as short, even though they are both at least several inches taller than the average American male. They seem short because their peers are so tall.

 

Perception

How do we organize certain sensations so that we perceive the poster that hangs on our wall or others so that we perceive a symphony? The term perception describes the process by which sensations are organized, as well as the product of this organization: an internal representation of some external stimulus. The fundamental task of perception is the recognition of and discrimination between different configurations of stimuli, a process known as pattern perception. Research converges to characterize the process and product as selective, coherent, creative, personal, and cultural. Since we process perceptions by meaning, all of those descriptions seem to follow.

 

Perception Is Selective

Our perception is selective which means that we do not simultaneously attend to all the stimuli occurring around us (Lavie & Tsal, 1994). In a crowded restaurant, you listen carefully to what your friend across the table is saying and not to conversations at other tables. On a bus, you look out the window to see how close you are to your intended stop; you are less likely to notice the clothing or cologne of your fellow passengers. You accord some stimuli more weight than other stimuli. The ease with which you can do this depends on the competing stimuli and attention processes (Kinchla, 1992). .

 

Perception Is Coherent`

To say that our perception is coherent is to say that conscious experiences are psychologically meaningful wholes. Remember S.B., whose story began this section? When he first gained sight, all he saw were blurs. But he quickly came to see the world in terms of discrete (coherent) objects.

 

Perception Is Creative

To say that our perception is creative means that it is not a literal version of reality but rather something we create. Among the raw ingredients of perception are, of course, our sensations, which are determined by external stimuli. However, perception is also determined by the habits, tendencies, and styles we bring to bear on our sensations (Wehner & Stadler, 1994).

 

Perception Is Personal

To say that our perception is personal is to say that we see the world from our own point of view. Most people say we see with our eyes, and hear with our ears. We see and hear with our brain and our brain has determined the meaning of the stimuli that we are processing. Therefore the stimulus has a specific meaning to us but not every one has the same specific meaning.  

 

Form Perception

To recognize an object, we use the principle of the figure-ground relationship. We group stimuli together into a unified form called a figure and distinguish the figure from surrounding stimuli, referred to as the ground. All perception of forms requires the organization of figures against backgrounds. Your perception may flip back and forth rapidly, but at any given moment you can see only one figure against one ground.

 

Psychologists have specified a number of principles that describe how we organize stimuli into coherent forms. These principles were first proposed by the Gestalt psychologists, and so they are called gestalt organizational principles of form perception. They include proximity, similarity, closure, and continuity.

 

Proximity is our tendency to group together stimuli that are near each other. Similarity refers to our tendency to group together stimuli that are similar in size, shape, color, or form. Moving to the right, you see not vertical columns of varied shapes but horizontal rows of dots and dashes, organized by the principle of similarity. According to the principle of closure, when an object has gaps, like the one in the lower left of the figure, you fill them in. What results in this case is a tiger. The tendency to smooth out irregularities also shows continuity, as you can see in the lower right of the figure. Current research into gestalt organizational principles attempts to locate just where they operate in the course of information processing. In contrast to the premise of the original Gestalt psychologists that perception of form takes place all at once and early in information processing, it now appears as if these principles result from several mechanisms operating at differing stages (Peterson & Gibson, 1994a, and 1994b). Consistent with this hypothesis is a case study of a 71-year-old woman with cortical degeneration (Kartsounis & Warrington, 1991). She could discriminate shapes when they were presented alone but not when they were overlapping. Her brain damage selectively affected her perception of forms.

 

Distance Perception

In everyday life, we judge distances all the time, usually with great accuracy. How far away is that approaching truck? How close is that fork wrapped in spaghetti? Explaining how people go about perceiving distance has been a major concern of psychologists (Gibson, 1988).

 

Remember that vision involves the projection of images onto the retina, where they stimulate neurons leading to the brain. These images contain no information about distance or depth. The projections of objects at differing distances might look exactly the same, if the objects are of appropriately different sizes. Why, then, do we have no trouble telling how far away an object is, whether it is under our nose, just beyond our reach, or somewhere over the rainbow? Think one more time of the example of S.B., and remember his difficulty perceiving distances. This might suggest that there is a “critical period” for depth perception.

 

Visual Constancies

Consider the following familiar experiences:

1.  You see a friend at the top of a staircase. As he walks down the stairs, his size remains constant. This becomes intriguing when you appreciate that the light stimulating your retina is constantly changing. In particular, the size of the retinal image constantly changes. Why do you not experience a change in your friend's size?

2.  You are reading this paragraph on a computer screen while slouching in a chair. As you tilt the screen away from you, it still maintains its rectangular shape. Again, this is intriguing. The retinal image changes from rectangular to trapezoidal as the screen tilts. Why do you not experience a change in the shape of the screen?

3.  You have switched to a new laundry detergent, and your pleasure knows no bounds because your clothes have never looked so bright. You walk down the street admiring the brightness of the sleeve of your favorite shirt. You pass beneath a large tree that shades the entire sidewalk, you, and your sleeve. You continue to admire how bright your clothes have become. Yet the intensity of light reflected by your shirt was greatly reduced when you walked under the tree. The amount of light stimulating your retina has changed. Why do you not experience a change in your shirt's brightness?

 

These examples illustrate visual constancies of size, shape, and brightness: the tendencies for visual perceptions to stay constant even as visual sensations change. As physical stimulation changes, our perceptual experiences remain constant. This phenomenon makes the world appear stable even though our moment-to-moment stimulation can fluctuate wildly. We somehow take into account factors besides the size, shape, or intensity of retinal stimulation (Wallach, 1987)?

 

Illusions

Perception psychologists have long been interested in illusions, phenomena in which our perception of an object is at odds with its actual characteristics. For example, the phi phenomenon refers to the fact that stationary objects in different locations are seen to move if they flash at the appropriate interval (about four to five times per second). This phenomenon is responsible for our perception of "motion" pictures as moving, when in fact they are composed of a series of stationary images.

 

Another type of apparent movement is the autokinetic effect, the tendency of a single point of light in a darkened room to appear to move, even when it is stationary. The autokinetic effect is caused by slight movements of our eyes while we fixate on the point of light (Matin & MacKinnon, 1964). We lack a context in which to locate the light, and we are unaware that our eyes are moving. Instead, we attribute the movement to the light itself. Apparent movement illustrates the gestalt truism that the whole (perception) is not the same as its parts (sensations).

 

Illusions give us an idea of how our sensory systems learned the environment and the price we pay for that learning. For example, people raised in a non-straight line environment are never fooled by straight line illusions as those raised in a straight line environment. The opposite is also true.

 

Perceptual Learning

Certain ways of structuring sensations are built into our nervous system (Hubel & Wiesel, 1962, 1979). Some believe that infants come into the world already equipped with certain feature detectors. For instance, Johnson, Dziurawiec, Ellis, and Morton (1991) showed that in the first hour following birth, infants are more likely to track a moving stimulus that looks like a face than they are to track similar but non-face like stimuli. Some believe that this tendency reflects the operation of an evolved mechanism, i.e. the newborn is predisposed to attend to the most important aspect of the environment--the parent--and the parent's attention in turn is drawn to the responsiveness of the infant. However, research indicates that infants prefer complex visual stimuli over relatively simple stimuli. One of the most complex visual stimuli is the human face (Langolois, 1999). Infants also prefer attractive faces to plain faces (Langolois, 1999).

 

But feature detectors are merely components in perception. If these are not used, they lose their capacity. Blakemore and Cooper (1970) raised kittens in such a way that for the first five months of their lives, they saw only vertical (or horizontal) stripes. As adult cats, these animals were unable to perceive horizontal (or vertical) stimuli. They were unresponsive to a stick waved at them unless it was presented in the same orientation with which they had early experience: vertical or horizontal.

 

With age and experience, the individual learns to organize the basic components of perception in more sophisticated ways. Children become increasingly able to recognize patterns (Alberti & Witryol, 1990).  That young children do not perceive patterns as readily as adults explains why lullabies across different cultures have simpler melodies than other songs from the same cultures do (Unyk, Trehub, Trainor, & Schellenberg, 1992). We sing lullabies to infants in order to soothe them. If the melody is too complex, they cannot grasp it, and they (and we) will be sleepless. Speech directed to infants is similarly simple, in terms of rhythm, pattern, and  soft phonemes.

 

Perceptual Sets

The second way in which perception is personal is that psychological states and characteristics influence what and how we perceive. We often perceive what we expect to perceive. A perceptual set (or mental set) is a predisposition to perceive a particular stimulus in a particular context.

 

Perceptual sets can be created in different ways. Perceptual sets may result from habitual experiences, prevailing needs like hunger or thirst, emotions, personality characteristics, or social pressures (Beck, Neeper, Baskin, & Forehand, 1983; Logan & Goetsch, 1993; Palfai & Salovey, 1992; Toner & Gates, 1985).

 

Stereotypes may produce perceptual sets, leading us to see individuals in a stereotyped group only in terms consistent with the stereotype. For example, Gibbons and Kassin (1987) presented artwork to research participants and described the artists as either retarded or nonretarded children. Although the paintings and drawings were identical, those attributed to retarded children were seen as less skilled.

 

A perceptual set is useful to the degree that it leads us to perceive stimulus characteristics that are relevant to the purpose at hand. In such cases, a perceptual set leads to more efficient processing of information (Auerbach & Leventhal, 1973; Macrae, Milne, & Bodenhausen, 1994). For instance, when I am grading a student's test, I attend to the content of what is written and not whether a pen or pencil was used. In other cases, a perceptual set channels information processing in the wrong direction (Dustman et al., 1984). Again, while grading a test, I may be looking only for the typical right answer and so may inadvertently ignore an unusual but equally correct one.

 

Perception Is Cultural

Perception is also influenced by our larger social context. We can thus characterize perception as cultural. Our culture directs our attention to some stimuli rather than others, dictates how we group together configurations of stimuli and distinguish them from one another, and provides concepts with which we interpret stimuli. Accordingly, a round red light is seen as a signal to stop in cultures with automobiles but as something different in cultures without. As pointed out in the discussion of perceptual sets, we are greatly influenced by our expectations. One of the important sources of these expectations is cultural beliefs and practices. To the degree these differ across cultures, then so to do perceptions (Deregowski, 1980; Tajfel, 1969).

 

Susceptibility to Illusions

Researchers have studied the susceptibility to illusions of people in different cultures. Differences exist, and these are interpretable in terms of the characteristic experiences provided by culture. A well-known investigation along these lines was conducted by Segall, Campbell, and Herskovitz (1963, 1966), who studied individuals from 15 different cultures, both European and non-European, in terms of their responses to the Müller-Lyer illusion. In general, Europeans were more susceptible to this visual illusion than non-Europeans, meaning that they tended--incorrectly--to perceive the right line as longer than the left line. In contrast, non-Europeans tended--correctly--to see the two lines as the same length.

 

Segall and his colleagues interpreted this difference in terms of the degree to which individuals were accustomed to a "carpentered" environment: a visual setting dominated by rectangularly shaped buildings. Recall one of the interpretations of the Müller-Lyer illusion: People see the lines as corresponding to outside corners of rooms versus inside corners. European individuals have more experience with rooms like these, and so they are more prone to the illusion.

 

As noted, other interpretations of this illusion are possible. Jahoda (1966), for instance, argued that the documented cultural differences are due to variations in experience with two-dimensional representations of three-dimensional objects. Those in European cultures have a lifelong familiarity with such drawings and have learned to regard certain artistic conventions as distance cues. So, they perceive the Müller-Lyer illusion in these terms. Those without such familiarity do not bring these expectations to bear on the lines. Thus, they do not misinterpret what they see. Mundy-Castle (1966) showed children from non-European cultures these pictures and asked them to answer such questions as:

1.  What do you see?

2.  What is the man doing?

3.  Can the deer see the man?

4.  Which is closer to the man: the elephant or the deer?

Research subjects correctly identified each item in the pictures, but they tended to interpret the pictures in two-dimensional terms, not making use of distance cues. This does not mean that these subjects were insensitive to distance in their everyday lives. Rather, they were unfamiliar with the conventions of European drawings used to signify distance.

 

Binocular Rivalry

Another demonstration of how culturally provided expectations influence perception is a study by Bagby (1957), who investigated the phenomenon of binocular rivalry. In binocular rivalry, different visual stimuli are shown separately to an individual's two eyes. Under appropriate circumstances, one image may dominate the other and be the only one the individual perceives.

 

Bagby's research subjects were from either Mexico or the United States; they were shown pairs of photographic slides for a few seconds, separately to each eye; and they were asked to describe what they saw. One slide depicted a characteristic Mexican scene (a bullfight), the other a characteristic United States scene (a baseball game). Results were clear-cut: The Mexican subjects selectively perceived the familiar Mexican scene, whereas the United States subjects selectively perceived the familiar United States scene.

 

Culture and Sensation

Perception is the psychological interpretation of sensations, and so it is perhaps not surprising that culture can influence perception. The less obviously answered question is whether culture affects sensation. The answer seems to be that it does not. Other than the threshold differences mentioned earlier, the biological characteristics of people's sensory systems are essentially the same. Culture influences attention, of course, but there is little reason to think that it influences sensation.

 

Pain

Let us conclude by discussing pain, another example of an integrative phenomenon. Pain is often described as a sensation and specifically as a cutaneous sense. However, this conceptualization is oversimplified. Stimuli that touch our skin may cause pain, but the sensation of pain is not limited to the stimulation of cutaneous receptors. Pain can and does occur through any sensory receptor. Deafening sounds, blinding lights, and overwhelming tastes produce pain just as readily as damaged skin. Pain from different sensory sources is readily combined in experience in a way that other sensations from different receptors are not (Algom, 1992). For instance, a moderately painful sound coupled with moderately painful pressure can produce a profoundly painful experience, yet it is the pain that is combined, not the sound and the touch.

 

Characterizing painful stimuli in terms of their simple physical properties proves difficult. Although pain usually results from intense stimuli, this generalization is not always true. Compare a pulsating shower with the prick of a pin. The water from the shower produces much more neural activity than the pin, but it is the pin that produces pain, not the shower.

 

In short, pain is a psychological puzzle. We can characterize it: Pain is unpleasant. We can describe its adaptive function: Pain serves as a warning signal that our well-being is threatened. We can note its powerful effect on behavior: Pain is something we try to avoid or escape. But we cannot--in a definitive way--say what pain is. Perhaps the puzzle results from the assumption that pain is just a sensation. Some psychologists argue that pain shares more in common with motives like hunger or thirst than it does with sensations like vision or taste (Price, 1988). Motives are experiences that impel us to behave in certain ways. Pain fits this definition. It has a sensory component--as do hunger and thirst--but this component must be understood within its larger context.

 

There are well-documented differences among cultural groups in their willingness and ability to tolerate intense stimuli (Fabrega, 1989; Ots, 1990; Pugh, 1991; Thomas & Rose, 1991; Villarruel & Ortiz de Montellano, 1992; Zborowski, 1969). For instance, in comparison to women from other ethnic groups, those from Asian cultures report more pain when having their ears pierced. The stereotype of Northern Europeans as stoic seems to have a basis in fact because many of these individuals can tolerate what would seem to be highly painful stimuli without complaint.

 

Similarly, Northern Europeans are less likely than those from most other cultural groups to experience chronic pain disorders (Hes, 1958, 1968). More than those from other cultural groups, European Americans expect to control how they feel (Bates & Rankin-Hill, 1994), whether or not they actually can (Peterson, Maier, & Seligman, 1993). These expectations in turn are associated with a decreased perception of pain (Averill, 1973; Miller, 1979; Thompson, 1981). Taken together, these findings again show how culture affects our experience of stimuli.

 

A contextualized view of pain is contained in gate-control theory (Melzack, 1973). According to this account, the nervous system is limited in the amount of sensory information it can handle at a given time. When too much information is present, cells in the spinal cord act as a gate, blocking some signals from going to the brain, while letting others pass. The brain may send messages to the spinal cord to open or close this hypothesized gate. Most of us have sustained an injury in the course of an engaging activity, like playing a sport, wherein we did not notice the gash in our leg or our chipped tooth until the activity ended. Presumably, the pain gate had been closed.

 

Perhaps people troubled by chronic pain have pain gates that stay open too long, for biological or psychological reasons. Accordingly, psychologists can help if they can devise a way to close the hypothesized gates. Endorphins may be involved in the gating of pain (Basbaum & Fields, 1984). Some psychologists believe that the Chinese practice of acupuncture controls pain because it closes particular gates (Chapman, Wilson, & Gehrig, 1976). Other strategies for controlling pain include drugs, massage, hypnosis, relaxation, and distraction (Caillet, 1993; Hamill & Rowlingson, 1994).

 

Pleasure

It is noteworthy that psychologists have studied pain extensively while paying relatively little attention to pleasure (Glick & Bone, 1990). Regardless, the points just made about pain also clarify pleasure. Pleasure has a sensory component, but it is not limited to any given sensory receptor. We experience pleasure through touch, smell, taste, vision, and so on. Pleasure exerts a powerful influence on our behavior. Finally, it is difficult, if not impossible, to characterize a pleasurable stimulus in terms of its simple physical properties. For example, we may experience hot water as pleasurable when we are taking a shower but as painful when we are merely touching it, even though it is the same temperature (Hermann, Candas, Hoeft, & Garreaud, 1994). Depending on what else is occurring, the identical sensory stimulation can produce pleasure, indifference, pain, or even revulsion.

 

Pleasure may best be regarded as a motive behind behavior. It is influenced by a host of biological, psychological, and social factors. In the modern Western world, for instance, most of us find a kiss to be highly pleasurable. But kissing is not among the cultural practices of all groups. Those in traditional Chinese and Japanese societies did not kiss one another (Ford & Beach, 1951).  

 

Attention

Orientation of Attention

Orientation refers to the positioning of our sense organs to best receive environmental stimulation. Intense stimuli demand our attention. Our prevailing needs and goals also direct our attention. We stare at objects we want to see; we stick our nose over objects we want to smell; we place our ears close to objects we want to hear. These are all examples of overt orientation. Psychologists are also concerned with covert orientation, which occurs when we direct our attention to stimuli without physically moving our sense organs (Posner, 1978): "Don't turn around and stare, but check out who just walked in the room." Covert orientation implies that attention does not occur solely through our senses but also involves top-down processes.

 

Divided Attention

Divided attention describes our ability to attend to different stimuli at the same time. As we learn to perform a task, we need to attend to its details less and less. Performance becomes automatized, and our attention can be deployed elsewhere. Consider driving a car. When you first slid behind the wheel of an automobile, the amount of stimulation overwhelmed you.

 

So many things competed for your attention: steering wheel, brakes, accelerator, turn signal, speedometer, pedestrians, school crossings, and other cars. With experience, you can do all sorts of things while driving, including listening to the radio, carrying on a conversation, and even watching the gas gauge.

 

Selective Attention

Another topic of interest concerns selective attention (Johnston & Dark, 1986). You can tune in some information while tuning out other information. Tuned-in information is front and center in our conscious experience, but what about tuned-out information? One way researchers answer this question is through studies of shadowing. They place headphones on a research subject and deliver one message to the right ear and another message to the left ear. The subject is asked to repeat one of the messages out loud (to shadow the message), under the assumption that he or she will therefore pay more attention to it. The typical finding is that subjects completely shut out the non-shadowed message. When asked later to recall its content, a subject can report nothing. He or she may not even know what language was spoken (Cherry, 1953). Other studies suggest that selective attention is more complex. If the non-shadowed message contains the subject's name, the subject notices it at least some of the time (Moray, 1959; Wood & Cowan, 1995).

 

How does Attention Work?

People can also learn to improve their attention (Pashler, 1992). Specific instructions and practice are helpful, even among the elderly (Kramer, Larish, & Strayer, 1995; Trudeau, Overbury, & Conrod, 1990). Stoffregen and Becklen (1989) showed, for instance, that with practice, people can improve their ability to divide attention between two complex tasks.