Gibson’s Perceptual Development Theory
Gibson’s Perceptual Development Theory - We tested 36 infants ranging in age from 6 months to 14 months on the visual cliff. Each child was placed upon the center board, and his mother called him to her from the cliff side and the shallow side successively. All of the 27 infants who moved off the board crawled out on the shallow side at least once; only three of them crept off the brink onto the glass suspended above the pattern on the floor. Many of the infants crawled away from the mother when she called to them from the cliff side; others cried when she stood there, because they could not come to her without crossing an apparent chasm. The experiment thus demonstrated that most human infants can discriminate depth as soon as they can crawl.
Biographical Sketch
Eleanor J. Gibson’s studies in psychology began at Smith College, from which she graduated in 1931. She then stayed on as a teaching assistant and married a young faculty member, James Gibson, who also was to become an eminent psychologist. In 1933 she earned her master’s degree with a thesis on learning. Subsequently, she became an instructor at Smith and attended the Gestaltist Kurt Koffka’s lectures regularly. Gibson moved on to Yale, hoping to study animal behavior, but instead studied people. In 1938, she obtained a Ph.D. under Clark Hull, the great learning theorist, at Yale. Gibson, however, did not feel intellectually comfortable in the stimulus–response learning climate of Yale. Her husband’s relocation for military service during World War II temporarily interrupted her career. When the Gibsons went to Cornell, she became a unpaid research associate for 16 years (due to nepotism rules). They then spent their careers developing an ecological approach to perception.
Gibson’s work in the 1950s and 1960s developed the new fields of perceptual learning and perceptual development. At Cornell she studied goats and sheep at the “Behavior Farm.” One study, on maternal–infant bonding in goats, was never completed because the baby goats’ caretaker inadvertently gave some of them away (Caudle, 2003). Gibson then studied babies on “visual cliffs” and children in reading-related situations in the laboratory. She became a professor at Cornell in 1966. Her book Principles of Perceptual Learning and Development (1969), which won the Century psychology prize, was hailed as one of the most influential books on development at that time (Hartup & Yonas, 1971). Her theory provided an alternative to learning theory and Piagetian approaches. In the next decade, she continued her wide-ranging research but turned her attention more and more to how children learn to read. Some of this work is summarized in The Psychology of Reading (1975), coauthored with Harry Levin. She then returned to the area of infancy, to study early perceptual development. Cornell honored her with an appointment as the Susan Linn Sage Professor Emeritus of Psychology, and she thus became the first woman to hold an endowed professorship at Cornell. Years after her “retirement,” she continued her research and writing (e.g., Gibson & Pick, 2000). She died in 2002 at age 92.
Her profession awarded Gibson many honors, including the Gold Medal Award, the Distinguished Scientific Contribution Award, and the G. Stanley Hall Award for Distinguished Contributions in Developmental Psychology from the American Psychological Association; the Howard Crosby Warren Medal from the Society of Experimental Psychologists; and the Distinguished Scientific Contribution Award from the Society for Research in Child Development. In addition, she was awarded the National Medal of Science—the nation’s highest scientific honor—and was elected to the National Academy of Sciences, the American Academy of Arts and Sciences, and the National Academy of Education.
General Orientation to The Theory
Gibson’s theory concerns perception, broadly defined. She asks four questions (Gibson & Pick, 2000): What do children perceive? How do they pick up this information? What actions or interactions take place? What are the consequences for knowledge? The following three sections examine characteristics of the theory that show how Gibson addressed these questions: the ecological approach, the notion that information for erception is specified in stimulation, and the active nature of human perceivers. The final section in this orientation examines her use of experimental methods that simulate natural environments.
Ecological Approach: Affordances
Only a theorist with an ecological perspective would ask Gibson’s four questions because the questions address the function of perception in real settings. People need to perceive objects, spatial layouts such as floors or the ground, and temporal events in order to adapt to the world: to walk around in it, find things in it, play in it, and even survive in it. These stimuli are complex relational units, such as objects and events, not simple sensations of light or sound. Thus, unlike most theories of perception, Gibson’s theory stressed what perceivers do in natural environments.
Gibson’s research and theorizing centered on affordances, a concept introduced by James Gibson (e.g., 1979b). Affordances are what an environment offers or provides for an organism; they are opportunities for action. Humans’ environments “afford” surfaces of support for walking or crawling, objects for grasping, passageways allowing movement, and
barriers preventing movement. Even the social environment offers affordances, for example, a smiling or angry face affords positive or negative interactions. Thus, the person and the environment fit together to form a whole, with a meshing of the person’s activities and the environment’s affordances. The utility of a property of the environment depends on the capacities of the organism. If an infant cannot yet walk, a solid surface does not afford “walking on.” Affordances thus involve a relationship between the organism and its surroundings. Gibson claimed that these affordances are perceived directly: “We do not perceive stimuli or retinal images or sensations or even just things; what we perceive are things that we can eat, or write with, or sit down on, or talk to” (1982, p. 60).
As children acquire new motor skills during development, they discover new affordances. When children start to walk, they learn to perceive whether a surface affords solid support for walking. This affordance is irrelevant for, and unknown to, a younger infant. In one experiment (Gibson et al., 1987), infants were placed on a walkway raised 4 feet from the floor. Their smiling mothers stood 6 feet away at the other end of the walkway. The walkway for one condition was a rigid surface (strong plywood covered with a patterned fabric), which affords locomotion for both crawling and walking. In the other condition, the walkway was a patterned fabric on a water bed, which affords crawling but not walking. The infants who could walk looked at and felt the water bed more than the rigid surface before they either walked on the rigid surface or crawled onto the water bed. The infants who could only crawl showed little, if any, differentiation of the two surfaces; they readily moved onto both of them. Thus, there is a fit between what the environment provides and the child’s actions, goals, and abilities.
Like ethologists (see Chapter 7), Gibson emphasized that the human species has evolved adaptive ways of perceiving the world. Each species is specialized for perceiving complex relations among stimuli specifying critical information in its environment. For example, bats are pretuned to use acoustic information (interpreting feedback from sounds) to help them navigate in dark caves. Birds and primates rely heavily on their visual perception of the spatial layout, prey, and predators, and hands permit humans and other primates to detect whether an object can be grasped and manipulated. Thus, what information an organism extracts from the environment depends on the species. The organism directly perceives affordances because the species has evolved a perceptual system that detects, or can learn to detect, the affordances that increase the likelihood of survival. The environment affords food, mates, and places to hide from predators.
Experience creates new affordances. Thus, within a species, individuals vary in their ability to use potential affordances: “A three-inch-wide beam affords performing backflips for a gymnast, but the affordance is not realizable by others; rock climbers learn to use certain terrains for support that do not appear to others to provide a surface of support” (Gibson & Pick, 2000, p. 17). Children’s evolutionary heritage provides the perceptual equipment and motivation to perceive—or learn to perceive— the particular objects, events, and spatial layouts that they need in that setting. By exploring and playing, children learn the affordances of objects, events, and surfaces.
Information Is Specified in Stimulation
To begin to understand Gibson’s answer to her first question, about what is perceived, we must understand her conception of the role of stimulation in perception. Her description of the active, self-motivated child exploring the stimulus world at first seems quite similar to Piaget’s view of children. The theorists part, however, in their conceptions of how children “know” the world through activity. Piagetian children “construct” their knowledge by forming schemes based on their motor behaviors with objects. Because perception produces static images, it must be corrected by operational knowledge. Similarly, other cognitive and perceptual approaches see perception as an act of enriching a sparse, ambiguous, uninformative retinal image that needs to be enriched by knowledge. For instance, information-processing approaches describe processes that add meaning to the stimulus by relating it to memories and knowledge in the long-term store. They refer to going beyond the information given by making inferences based on knowledge of the world.
In contrast, Gibson believed that stimulation is a rich source of information that specifies objects, events, and surfaces. The developmental issue, then, is how children learn to extract more and more information from that stimulation. As children perceive, they differentiate information, rather than add to it. The assumption that complex information is inherent in stimulation is the most controversial claim in the theory. It is important, therefore, that we consider this claim carefully. Information extends over time and space as people and objects move. That is, stimulation is not static and frozen in space and time. As Gibson commented, “There is no shutter on the retina, no such thing as a static image” (1988, p. 5). Stimulation specifies events, places, and objects.
Thus, if children can extract this information, they perceive events, places, and objects and understand how the affordances fit with their abilities. They do not perceive a single, discrete “stimulus,” such as an object. Rather, from the entire spatiotemporal array, they perceive the information that specifies particular objects. In other words, stimulation is a field of available information about affordances to be differentiated. Stimulation carries many levels of information. At the simplest and most concrete level, a child discriminates objects by one or several distinctive features, or attributes, that differentiate them. Suppose a boy moves near an ocean and for the first time in his life encounters hundreds of shells. He
begins a collection and attempts to identify the shells with the help of a field guide with photographs. Although he is perceptually capable of telling all of the shells apart if he places them side by side, he actually notices only a few distinctive features at first, perhaps only salient differences in color, shape, and size. Only after much playing with the shells and comparing them with each other and with the pictures in the book does he realize that the stimulus class “shells” has a particular set of distinctive features that allows him to determine the appropriate label for each shell. Although size is a salient feature, it is seldom important for differentiating types of shells.
In contrast, slight differences in the shape of the “crown” at the top of the shell or subtle differences in the colored pattern on the shell are quite important. Although this information was in the light stimulating the boy’s eyes from the start, he did not really notice it or abstract it as a defining feature until he had more perceptual experience with the shells.
At a more abstract level of analysis, we can perceive a higher-order structure to light or sound. A good example is the musical pattern we call a melody. We abstract a melody from a succession of notes played on the piano. We recognize this melody as the same melody even if it is transposed to a different key or played at a different tempo or on a saxophone instead of a piano. The pattern is there in stimulation, but we may not have perceived it at first. Thus, perceptual learning is a process of learning to perceive what has always been there. Gibson has noted that her theory might be called a “seek and ye shall find” theory (1977, p. 157). Young children, having limited experience with objects and events in the world, often do not perceive subtle differences in the appearance of objects or patterns (organized light). They must search out these differences.
It is instructive to carry the musical example to perceptual learning. When we hear a new orchestral work, we have a relatively undifferentiated perception of the work after the first hearing. Only after listening to the work several times are we able to extract melodies and their transformations, grasp the overall structure of the piece, and perhaps even differentiate the various instruments of the orchestra. For most people raised in the West, this task is more difficult with Eastern music or modern compositions using the 12-tone scale, which are less familiar than with the first hearing of yet another Haydn symphony. In this musical example, stimulation has remained the same throughout the repeated hearing. What has changed is what information we have extracted.
In the beginning we listened yet did not hear. We gradually perceived more and more of what had always been there. Our perception became both more specific, as we became aware of subtle musical qualities, and more abstract, as we perceived musical patterns. Thus, the information is in the stimulation, but sometimes we must learn to perceive it. Our perception improves not by filling in the raw auditory stimulus by adding words or applying schemes, not by cognitively gluing together the notes, but by listening to the music and directing our attention. We attend to relational information—distinctive features and patterns concerning relationships among the parts—not to bits and pieces of information. In Gibson’s words:
“There is structure in the array, relational information that does not have to be pieced together because, like truth, it is already there. This is the assumption I want to proceed with. I do not want a construction theory, with processors at every stage like an assembly line”
(1977, p. 157).
Information about the self also is important. Children must extract proprioceptive stimulation from their body in movement and detect information about their own effectiveness at making their way around their world. In this way they can perceive the relation between the environment and the self that together specify an affordance. Toddlers must be able to judge whether they can walk down a slope of a particular angle in order to detect whether the perceptual information about the slope specifies the affordance “walkability.”
Humans as Active Perceivers
No parent would be surprised by the claim that children seem to be constantly in motion. Parents might, however, be surprised by the claim that this motion is essential to perceptual development, even in infancy. Gibson often referred to “the perceiver as performer” (Gibson & Rader, 1979). In her view, perception is an event. Children and adults discover, explore, attend, extract information, and differentiate objects, events, and arrays. These are the behaviors of an active organism that does something in order to learn about the world. Gibson held an interactionist view of perception and action. Children act to discover the information, and by discovering information, they can act. They actively extract affordances and by using them discover new affordances. For example, children may perceive the affordances of various types of balls by kicking them, rolling them, and trying to bounce them. By then using them in a game for which they are suited, children discover new affordances, such as passing the ball to teammates. This is Gibson’s answer to her second question, about how information is picked up. Children actively perceive while dong things in their world.
Humans, as a species, are inherently motivated to explore and learn about their world. There are, however, goals and needs specific to each task or situation. A girl putting together a puzzle attends to shape and color because these attributes are information she needs to achieve her goal of completing the puzzle. A baby learning to walk must be very attentive to the position of her body in space and the distance between furniture.
Young soccer players seek a different sort of information. They continually search for and track the ball, perceive the spatial relationship between other players and the ball, and use feedback concerning their attempts to kick the ball (falling down, kicking erratically, and so on). Adult mountain climbers are more attentive to where they place each step than are people taking a leisurely walk (Gibson & Rader, 1979) in these examples, there is a relationship—ideally, a match—between the person’s goals and the information extracted from the environment.
Methodology
Although Gibson’s research, as well as other research stimulated by her theory, followed the experimental procedures of other areas of developmental psychology, it was unusual in one way. It tried to retain ecological validity in the experimental setting. This does not mean that
Gibsonians necessarily observe perceptual activities in their natural settings. It does mean that they attempt to simulate (mimic important features), in the experimental setting, the stimulation, tasks, and goals of the child’s natural environment. We can see the close connection between theory and methods in the materials and procedures Gibsonians select for their experiments. Multimodal stimulation (for example, faces that move and make sounds and objects that can be touched), various kinds of environmental supports for locomotion (for example, solid or nonsolid surfaces), and opportunities for obtaining feedback from exploratory activities (and thus detecting contingencies) are found in both the child’s daily life and in Gibson’s laboratory.
In an early experiment on depth, for instance, Gibson, along with Walk (1960), constructed a “visual cliff,” which simulates a cliff or dropoff in the real world. Gibson was inspired to create this miniature Grand Canyon after visiting the real Grand Canyon with her young child and pondering, with some concern, the child’s ability to perceive it as a drop-off. The visual cliff is a table with a glass top that gives the impression of a solid surface on one-half of the table; on the other half of the table, the floor is visible through the glass. Thus, the apparatus displays information specifying a drop-off. Some of the results were described at the beginning of this chapter. Infants will crawl on the “cliff ” half, but refuse to crawl onto the half of the glass that hangs over the apparent “thin air.” The visual-cliff experiments demonstrated that children perceive depth at an edge at least as early as 6 or 7 months, when they begin to crawl. Research using heart rate indicated that even younger infants differentiate the cliff and noncliff sides (Campos,Langer, & Krowitz, 1970). The visual cliff has been used widely to study depth perception in many species. In fact, early on, Gibson had puzzled over why a newborn goat, when placed on a small, high stand to get it out of the way while its twin was being delivered, knew to stand motionless n this high surface (Caudle, 2003).
Applications
Gibson’s book on reading, mentioned earlier, showed that perceptual learning about letters, correspondences between letters and sounds, and the structure of sentences is essential for learning to read. In addition, her theory suggests that to a great extent children can educate themselves about the world just by moving around in it. A preschool teacher can provide interesting and varied objects and surfaces and let young children learn by exploring that world. Perceptual learning also is essential for children’s safety and health. Being able to judge the slipperiness of surfaces and the lack of support offered by a rickety bridge railing is essential for avoiding serious accidents. Finally, the importance her theory places on learning about the world through activity implies that the “obesity epidemic,” reflecting physical inactivity to a great extent (“couch-potato” parents and “tater-tot” children), may hurt children’s learning and self-regulation (e.g., Davis et al., in press).
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| image source: www.simplypsychology.org |
GIBSON & WALK, 1960, p. 64
On uphill trials [on slopes in a laboratory] infants often attempted hills where they were likely to fall, despite falling on previous trials and in previous sessions. Crawlers usually struggled at the base of impossibly steep slopes for the entire duration of the trial, sometimes getting partway up, then sliding back down. After lengthy frustrated attempts, they tried equally hard moments later at the next impossibly steep slope. Walkers usually adopted a similar strategy, getting a running headstart on two feet and flinging themselves at impossibly steep inclines. Sometimes persistence paid off and infants eventually reached the summit.
On uphill trials [on slopes in a laboratory] infants often attempted hills where they were likely to fall, despite falling on previous trials and in previous sessions. Crawlers usually struggled at the base of impossibly steep slopes for the entire duration of the trial, sometimes getting partway up, then sliding back down. After lengthy frustrated attempts, they tried equally hard moments later at the next impossibly steep slope. Walkers usually adopted a similar strategy, getting a running headstart on two feet and flinging themselves at impossibly steep inclines. Sometimes persistence paid off and infants eventually reached the summit.
ADOLPH & EPPLER, 1999, p. 40
Biographical Sketch
Eleanor J. Gibson’s studies in psychology began at Smith College, from which she graduated in 1931. She then stayed on as a teaching assistant and married a young faculty member, James Gibson, who also was to become an eminent psychologist. In 1933 she earned her master’s degree with a thesis on learning. Subsequently, she became an instructor at Smith and attended the Gestaltist Kurt Koffka’s lectures regularly. Gibson moved on to Yale, hoping to study animal behavior, but instead studied people. In 1938, she obtained a Ph.D. under Clark Hull, the great learning theorist, at Yale. Gibson, however, did not feel intellectually comfortable in the stimulus–response learning climate of Yale. Her husband’s relocation for military service during World War II temporarily interrupted her career. When the Gibsons went to Cornell, she became a unpaid research associate for 16 years (due to nepotism rules). They then spent their careers developing an ecological approach to perception.
Gibson’s work in the 1950s and 1960s developed the new fields of perceptual learning and perceptual development. At Cornell she studied goats and sheep at the “Behavior Farm.” One study, on maternal–infant bonding in goats, was never completed because the baby goats’ caretaker inadvertently gave some of them away (Caudle, 2003). Gibson then studied babies on “visual cliffs” and children in reading-related situations in the laboratory. She became a professor at Cornell in 1966. Her book Principles of Perceptual Learning and Development (1969), which won the Century psychology prize, was hailed as one of the most influential books on development at that time (Hartup & Yonas, 1971). Her theory provided an alternative to learning theory and Piagetian approaches. In the next decade, she continued her wide-ranging research but turned her attention more and more to how children learn to read. Some of this work is summarized in The Psychology of Reading (1975), coauthored with Harry Levin. She then returned to the area of infancy, to study early perceptual development. Cornell honored her with an appointment as the Susan Linn Sage Professor Emeritus of Psychology, and she thus became the first woman to hold an endowed professorship at Cornell. Years after her “retirement,” she continued her research and writing (e.g., Gibson & Pick, 2000). She died in 2002 at age 92.
Her profession awarded Gibson many honors, including the Gold Medal Award, the Distinguished Scientific Contribution Award, and the G. Stanley Hall Award for Distinguished Contributions in Developmental Psychology from the American Psychological Association; the Howard Crosby Warren Medal from the Society of Experimental Psychologists; and the Distinguished Scientific Contribution Award from the Society for Research in Child Development. In addition, she was awarded the National Medal of Science—the nation’s highest scientific honor—and was elected to the National Academy of Sciences, the American Academy of Arts and Sciences, and the National Academy of Education.
General Orientation to The Theory
Gibson’s theory concerns perception, broadly defined. She asks four questions (Gibson & Pick, 2000): What do children perceive? How do they pick up this information? What actions or interactions take place? What are the consequences for knowledge? The following three sections examine characteristics of the theory that show how Gibson addressed these questions: the ecological approach, the notion that information for erception is specified in stimulation, and the active nature of human perceivers. The final section in this orientation examines her use of experimental methods that simulate natural environments.
Ecological Approach: Affordances
Only a theorist with an ecological perspective would ask Gibson’s four questions because the questions address the function of perception in real settings. People need to perceive objects, spatial layouts such as floors or the ground, and temporal events in order to adapt to the world: to walk around in it, find things in it, play in it, and even survive in it. These stimuli are complex relational units, such as objects and events, not simple sensations of light or sound. Thus, unlike most theories of perception, Gibson’s theory stressed what perceivers do in natural environments.
Gibson’s research and theorizing centered on affordances, a concept introduced by James Gibson (e.g., 1979b). Affordances are what an environment offers or provides for an organism; they are opportunities for action. Humans’ environments “afford” surfaces of support for walking or crawling, objects for grasping, passageways allowing movement, and
barriers preventing movement. Even the social environment offers affordances, for example, a smiling or angry face affords positive or negative interactions. Thus, the person and the environment fit together to form a whole, with a meshing of the person’s activities and the environment’s affordances. The utility of a property of the environment depends on the capacities of the organism. If an infant cannot yet walk, a solid surface does not afford “walking on.” Affordances thus involve a relationship between the organism and its surroundings. Gibson claimed that these affordances are perceived directly: “We do not perceive stimuli or retinal images or sensations or even just things; what we perceive are things that we can eat, or write with, or sit down on, or talk to” (1982, p. 60).
As children acquire new motor skills during development, they discover new affordances. When children start to walk, they learn to perceive whether a surface affords solid support for walking. This affordance is irrelevant for, and unknown to, a younger infant. In one experiment (Gibson et al., 1987), infants were placed on a walkway raised 4 feet from the floor. Their smiling mothers stood 6 feet away at the other end of the walkway. The walkway for one condition was a rigid surface (strong plywood covered with a patterned fabric), which affords locomotion for both crawling and walking. In the other condition, the walkway was a patterned fabric on a water bed, which affords crawling but not walking. The infants who could walk looked at and felt the water bed more than the rigid surface before they either walked on the rigid surface or crawled onto the water bed. The infants who could only crawl showed little, if any, differentiation of the two surfaces; they readily moved onto both of them. Thus, there is a fit between what the environment provides and the child’s actions, goals, and abilities.
Like ethologists (see Chapter 7), Gibson emphasized that the human species has evolved adaptive ways of perceiving the world. Each species is specialized for perceiving complex relations among stimuli specifying critical information in its environment. For example, bats are pretuned to use acoustic information (interpreting feedback from sounds) to help them navigate in dark caves. Birds and primates rely heavily on their visual perception of the spatial layout, prey, and predators, and hands permit humans and other primates to detect whether an object can be grasped and manipulated. Thus, what information an organism extracts from the environment depends on the species. The organism directly perceives affordances because the species has evolved a perceptual system that detects, or can learn to detect, the affordances that increase the likelihood of survival. The environment affords food, mates, and places to hide from predators.
Experience creates new affordances. Thus, within a species, individuals vary in their ability to use potential affordances: “A three-inch-wide beam affords performing backflips for a gymnast, but the affordance is not realizable by others; rock climbers learn to use certain terrains for support that do not appear to others to provide a surface of support” (Gibson & Pick, 2000, p. 17). Children’s evolutionary heritage provides the perceptual equipment and motivation to perceive—or learn to perceive— the particular objects, events, and spatial layouts that they need in that setting. By exploring and playing, children learn the affordances of objects, events, and surfaces.
Information Is Specified in Stimulation
To begin to understand Gibson’s answer to her first question, about what is perceived, we must understand her conception of the role of stimulation in perception. Her description of the active, self-motivated child exploring the stimulus world at first seems quite similar to Piaget’s view of children. The theorists part, however, in their conceptions of how children “know” the world through activity. Piagetian children “construct” their knowledge by forming schemes based on their motor behaviors with objects. Because perception produces static images, it must be corrected by operational knowledge. Similarly, other cognitive and perceptual approaches see perception as an act of enriching a sparse, ambiguous, uninformative retinal image that needs to be enriched by knowledge. For instance, information-processing approaches describe processes that add meaning to the stimulus by relating it to memories and knowledge in the long-term store. They refer to going beyond the information given by making inferences based on knowledge of the world.
In contrast, Gibson believed that stimulation is a rich source of information that specifies objects, events, and surfaces. The developmental issue, then, is how children learn to extract more and more information from that stimulation. As children perceive, they differentiate information, rather than add to it. The assumption that complex information is inherent in stimulation is the most controversial claim in the theory. It is important, therefore, that we consider this claim carefully. Information extends over time and space as people and objects move. That is, stimulation is not static and frozen in space and time. As Gibson commented, “There is no shutter on the retina, no such thing as a static image” (1988, p. 5). Stimulation specifies events, places, and objects.
Thus, if children can extract this information, they perceive events, places, and objects and understand how the affordances fit with their abilities. They do not perceive a single, discrete “stimulus,” such as an object. Rather, from the entire spatiotemporal array, they perceive the information that specifies particular objects. In other words, stimulation is a field of available information about affordances to be differentiated. Stimulation carries many levels of information. At the simplest and most concrete level, a child discriminates objects by one or several distinctive features, or attributes, that differentiate them. Suppose a boy moves near an ocean and for the first time in his life encounters hundreds of shells. He
begins a collection and attempts to identify the shells with the help of a field guide with photographs. Although he is perceptually capable of telling all of the shells apart if he places them side by side, he actually notices only a few distinctive features at first, perhaps only salient differences in color, shape, and size. Only after much playing with the shells and comparing them with each other and with the pictures in the book does he realize that the stimulus class “shells” has a particular set of distinctive features that allows him to determine the appropriate label for each shell. Although size is a salient feature, it is seldom important for differentiating types of shells.
In contrast, slight differences in the shape of the “crown” at the top of the shell or subtle differences in the colored pattern on the shell are quite important. Although this information was in the light stimulating the boy’s eyes from the start, he did not really notice it or abstract it as a defining feature until he had more perceptual experience with the shells.
At a more abstract level of analysis, we can perceive a higher-order structure to light or sound. A good example is the musical pattern we call a melody. We abstract a melody from a succession of notes played on the piano. We recognize this melody as the same melody even if it is transposed to a different key or played at a different tempo or on a saxophone instead of a piano. The pattern is there in stimulation, but we may not have perceived it at first. Thus, perceptual learning is a process of learning to perceive what has always been there. Gibson has noted that her theory might be called a “seek and ye shall find” theory (1977, p. 157). Young children, having limited experience with objects and events in the world, often do not perceive subtle differences in the appearance of objects or patterns (organized light). They must search out these differences.
It is instructive to carry the musical example to perceptual learning. When we hear a new orchestral work, we have a relatively undifferentiated perception of the work after the first hearing. Only after listening to the work several times are we able to extract melodies and their transformations, grasp the overall structure of the piece, and perhaps even differentiate the various instruments of the orchestra. For most people raised in the West, this task is more difficult with Eastern music or modern compositions using the 12-tone scale, which are less familiar than with the first hearing of yet another Haydn symphony. In this musical example, stimulation has remained the same throughout the repeated hearing. What has changed is what information we have extracted.
In the beginning we listened yet did not hear. We gradually perceived more and more of what had always been there. Our perception became both more specific, as we became aware of subtle musical qualities, and more abstract, as we perceived musical patterns. Thus, the information is in the stimulation, but sometimes we must learn to perceive it. Our perception improves not by filling in the raw auditory stimulus by adding words or applying schemes, not by cognitively gluing together the notes, but by listening to the music and directing our attention. We attend to relational information—distinctive features and patterns concerning relationships among the parts—not to bits and pieces of information. In Gibson’s words:
“There is structure in the array, relational information that does not have to be pieced together because, like truth, it is already there. This is the assumption I want to proceed with. I do not want a construction theory, with processors at every stage like an assembly line”
(1977, p. 157).
Information about the self also is important. Children must extract proprioceptive stimulation from their body in movement and detect information about their own effectiveness at making their way around their world. In this way they can perceive the relation between the environment and the self that together specify an affordance. Toddlers must be able to judge whether they can walk down a slope of a particular angle in order to detect whether the perceptual information about the slope specifies the affordance “walkability.”
Humans as Active Perceivers
No parent would be surprised by the claim that children seem to be constantly in motion. Parents might, however, be surprised by the claim that this motion is essential to perceptual development, even in infancy. Gibson often referred to “the perceiver as performer” (Gibson & Rader, 1979). In her view, perception is an event. Children and adults discover, explore, attend, extract information, and differentiate objects, events, and arrays. These are the behaviors of an active organism that does something in order to learn about the world. Gibson held an interactionist view of perception and action. Children act to discover the information, and by discovering information, they can act. They actively extract affordances and by using them discover new affordances. For example, children may perceive the affordances of various types of balls by kicking them, rolling them, and trying to bounce them. By then using them in a game for which they are suited, children discover new affordances, such as passing the ball to teammates. This is Gibson’s answer to her second question, about how information is picked up. Children actively perceive while dong things in their world.
Humans, as a species, are inherently motivated to explore and learn about their world. There are, however, goals and needs specific to each task or situation. A girl putting together a puzzle attends to shape and color because these attributes are information she needs to achieve her goal of completing the puzzle. A baby learning to walk must be very attentive to the position of her body in space and the distance between furniture.
Young soccer players seek a different sort of information. They continually search for and track the ball, perceive the spatial relationship between other players and the ball, and use feedback concerning their attempts to kick the ball (falling down, kicking erratically, and so on). Adult mountain climbers are more attentive to where they place each step than are people taking a leisurely walk (Gibson & Rader, 1979) in these examples, there is a relationship—ideally, a match—between the person’s goals and the information extracted from the environment.
Methodology
Although Gibson’s research, as well as other research stimulated by her theory, followed the experimental procedures of other areas of developmental psychology, it was unusual in one way. It tried to retain ecological validity in the experimental setting. This does not mean that
Gibsonians necessarily observe perceptual activities in their natural settings. It does mean that they attempt to simulate (mimic important features), in the experimental setting, the stimulation, tasks, and goals of the child’s natural environment. We can see the close connection between theory and methods in the materials and procedures Gibsonians select for their experiments. Multimodal stimulation (for example, faces that move and make sounds and objects that can be touched), various kinds of environmental supports for locomotion (for example, solid or nonsolid surfaces), and opportunities for obtaining feedback from exploratory activities (and thus detecting contingencies) are found in both the child’s daily life and in Gibson’s laboratory.
In an early experiment on depth, for instance, Gibson, along with Walk (1960), constructed a “visual cliff,” which simulates a cliff or dropoff in the real world. Gibson was inspired to create this miniature Grand Canyon after visiting the real Grand Canyon with her young child and pondering, with some concern, the child’s ability to perceive it as a drop-off. The visual cliff is a table with a glass top that gives the impression of a solid surface on one-half of the table; on the other half of the table, the floor is visible through the glass. Thus, the apparatus displays information specifying a drop-off. Some of the results were described at the beginning of this chapter. Infants will crawl on the “cliff ” half, but refuse to crawl onto the half of the glass that hangs over the apparent “thin air.” The visual-cliff experiments demonstrated that children perceive depth at an edge at least as early as 6 or 7 months, when they begin to crawl. Research using heart rate indicated that even younger infants differentiate the cliff and noncliff sides (Campos,Langer, & Krowitz, 1970). The visual cliff has been used widely to study depth perception in many species. In fact, early on, Gibson had puzzled over why a newborn goat, when placed on a small, high stand to get it out of the way while its twin was being delivered, knew to stand motionless n this high surface (Caudle, 2003).
Applications
Gibson’s book on reading, mentioned earlier, showed that perceptual learning about letters, correspondences between letters and sounds, and the structure of sentences is essential for learning to read. In addition, her theory suggests that to a great extent children can educate themselves about the world just by moving around in it. A preschool teacher can provide interesting and varied objects and surfaces and let young children learn by exploring that world. Perceptual learning also is essential for children’s safety and health. Being able to judge the slipperiness of surfaces and the lack of support offered by a rickety bridge railing is essential for avoiding serious accidents. Finally, the importance her theory places on learning about the world through activity implies that the “obesity epidemic,” reflecting physical inactivity to a great extent (“couch-potato” parents and “tater-tot” children), may hurt children’s learning and self-regulation (e.g., Davis et al., in press).
That article about Gibson’s Perceptual Development Theory.
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