The Epigenesis of Mind

Essays on Biology and Cognition

Susan Carey, Rochel Gelman, Susan Carey, Rochel Gelman

• Publisher: Psychology Press
• Year: 2014
• Print ISBN: 9780805804386
• eBook ISBN: 9781317784630
• Topic: Psychologie
• Subtopic: Entwicklungspsychologie

Reflecting the focus of a Jean Piaget Symposium entitled Biology and Knowledge: Structural Constraints on Development, this volume presents many of the emergent themes discussed.

Among these themes are:

• Structural constraints on cognitive development and learning come in many shapes and forms and involve appeal to more than one level of analysis.
• To postulate innate knowledge is not to deny that humans can acquire new concepts.
• It is unlikely that there is only one learning mechanism, even if one prefers to work with general as opposed to domain-specific mechanisms.
• The problems of induction with respect to concept acquisition are even harder than originally thought.

II

INNATE KNOWLEDGE AND BEYOND

5	Physical Knowledge in Infancy: Reflections on Piaget’s Theory

Elizabeth S. Spelke

Cornell University

TWO PIAGETIAN THESES

This chapter focuses on two theses that are central to Piaget’s theory of the development of physical knowledge (Piaget, 1954, 1969, 1974). One thesis concerns developmental changes in conceptions of the world. The other thesis concerns the relation of knowledge to perception.

First, Piaget proposed that conceptions of the physical world undergo revolutionary change in infancy and childhood. The most dramatic changes occur in infancy. In Piaget’s view, young infants conceive of physical phenomena as emanating from their own actions. By the close of infancy, in contrast, children conceive the physical world as composed of objects, including themselves, whose behavior is governed by physical laws. For Piaget, this change was as radical as the conceptual changes that occur during scientific revolutions. In particular, Piaget and Inhelder (1969) likened the child’s construction of a world of physical objects to the construction, in 16th-century astronomy, of the heliocentric universe. The conceptual revolution in infancy may be deeper than the Copernican revolution, however, because astronomers throughout history have shared a view of the self in relation to the external world: a view that is not shared, Piaget believed, by infants.

Second, Piaget proposed that children’s conceptions are inextricably tied to their perceptions: Perception and thought are two aspects of a single developing capacity. In particular, the child who cannot conceive the world as composed of law-governed objects also cannot apprehend objects in his or her immediate surroundings: The child perceives a world of ephemeral appearances, not of stable and enduring bodies. Here again, a parallel is apparent between physical reasoning in infancy and in science. For example, the evolution of modern astronomy brought changes in scientists’ perception of the stars and planets: What were once seen as an array of concentric spheres rotating about the center of the earth were later seen as an arrangement of separated bodies in space (e.g., Kuhn, 1959; Toulmin & Goodfield, 1961). Since spheres are enduring parts of the physical world, however, the perceptual changes that infants experience, according to Piaget, are again more fundamental.

Both of Piaget’s theses have received considerable support. Concerning the first thesis, conceptual changes have been documented in the history of science (e.g., Crombie, 1952; Kitcher, 1988; Kuhn, 1962; Wiser & Carey, 1983), in studies of young adults learning science (White, 1988), and in studies of children’s spontaneous reasoning about physical phenomena (Carey, 1988; this volume; Karmiloff-Smith, this volume; Smith, Carey, & Wiser, 1985; Vosniadou & Brewer, 1990), as well as in the experiments of Piaget and his successors (e.g., Bower, 1982; Gopnik, 1988; Harris, 1983). Concerning the second thesis, evidence for a linkage between perception and thought has come from studies in the history of science (e.g., Jacob, 1972; Kuhn, 1962) and from analyses of the apparently rational character of perception (Descartes, 1638; Helmholtz, 1926; Rock, 1983). Piaget’s second thesis is also supported by (and springs from) arguments in philosophy concerning the impossibility of observation in the absence of some conceptual framework (Kant, 1929).

As noted, these theses suggest that the development of knowledge in children is similar to the historical development of knowledge in science and mathematics. Piaget viewed science and mathematics as human enterprises built upon abilities and activities that their practitioners share with ordinary adults and children. If that is true, then insights into the development of science and mathematics may shed light on the development of knowledge in children, and vice versa. Much of Piaget’s life was devoted to exploring this possibility and its consequences: “When I reason in terms of genetic psychology, I always keep in the back of my mind something based on the history of sciences or the history of mathematics, because it is the same process” (Piaget, 1980, p. 151). To deny the parallel between children and scientists is both to forego the possibility of these insights and to reject what appears to be the simplest and most general account of the development of human knowledge.

Despite these considerations, it is now difficult to maintain Piaget’s two theses jointly. Thirty years of research on the perceptual capacities of human infants provides evidence that infants’ perceptions of physical objects do not differ fundamentally from the perceptions of adults (see Banks & Salapatek, 1983; Gibson & Spelke, 1983; Yonas, 1988, for reviews). In particular, young infants do not appear to experience the array of ephemeral appearances described by Piaget but a world of stable, three-dimensional objects (Gibson, 1969; Kellman, 1988; Leslie, 1988; Slater, Mattock, & Brown, 1990; Spelke, 1982). Infants even apprehend the persistence of objects that are fully occluded (Baillargeon, 1987a, 1987b; Baillargeon, Spelke, & Wasserman, 1985). Although infants do not appear to perceive objects under all the conditions that adults do (see Spelke, 1990), the development of object perception would seem to be a process of enrichment, not of revolutionary change. This continuity in object perception is difficult to understand, if children’s perceptions reflect their physical conceptions and if those conceptions differ radically and fundamentally from the conceptions of adults.

A second problem arises from Piaget’s two theses: If infants perceive a radically different world from adults, it is not clear how children ever develop mature physical conceptions (see Kant, 1929; Koffka, 1935). A child whose conceptions led him or her to experience a succession of changing appearances rather than a layout of enduring objects might learn more and more about such appearances: when two appearances coincide, when one appearance follows another, and the like. The child’s perceptions would not lead him or her to believe, however, that the ephemeral character of experience is an illusion. Thus, an inextricable linking of perception to thought appears to lead in a circle, in which the conceptions that determine initial perceptions can only perpetuate themselves. Piaget recognized this circularity: That recognition, I believe, lies behind his argument that true knowledge does not come from perception (e.g., Piaget, 1954; see also Putnam, 1980). He has been criticized, however, for failing to provide an account of conceptual development that avoids this circularity (see Piatelli-Palmarini, 1980).

If the preceding findings and arguments are correct, then at least one of Piaget’s theses must be reconsidered. Many psychologists have proposed to abandon the second thesis and retain the first (Kellman, 1988; Leslie, 1988; Premack, 1990; for the guiding ideas behind this proposal, see Fodor, 1983; and Carey, 1985, 1988). According to this view, physical reasoning changes radically over development in ways that parallel conceptual change in science, but it is largely independent of the processes by which humans perceive objects. Object perception is based primarily on “modular” mechanisms: mechanisms that are largely innate and impervious to intention or belief. Thus, infants perceive objects in fundamentally the same ways as adults (and as scientists), but they reason about objects differently.

In this chapter, I suggest a different view. The processes by which humans perceive objects are inseparable from the processes by which humans reason about objects, just as Piaget believed (although other perceptual processes are distinct from physical reasoning). Physical reasoning and object perception do not, however, undergo revolutionary changes over human development. They develop through a process of enrichment around core principles that are constant. In these respects, the development of knowledge in infants and children may differ from the development of knowledge in science.

These suggestions are prompted by recent research on infants’ inferences about hidden objects and their motions. Before turning to this research, however, I must say more about the nature of early-developing physical knowledge and of the tasks through which it may be revealed. This discussion begins again with Piaget.

SIGNS OF PHYSICAL KNOWLEDGE IN INFANCY

As children, humans gain knowledge of many physical phenomena. For example, children become sensitive to some of the properties and behavior of heat (e.g., Piaget, 1974; Strauss, 1982), fluids (e.g., Piaget & Inhelder, 1962), solid substances (e.g., Smith et al., 1985), light and shadow (e.g., Piaget, 1930, DeVries, 1987), and celestial bodies (e.g., Piaget, 1929; Vosniadou & Brewer, 1990). In infancy, however, studies of physical knowledge have focused primarily on the properties and behavior of middle-sized material bodies, such as cups, rocks, and apples. This domain of knowledge is my focus as well.

Piaget viewed human knowledge of physical objects as the implicit appreciation of physical laws, or constraints, governing objects’ behavior. Although his writings contain no inventory of the constraints that humans come to appreciate, five constraints figure prominently in his experiments: continuity (objects exist continuously and move on connected paths), solidity (objects occupy space uniquely, such that no parts of two distinct objects coincide in space and time), no action at a distance (distinct objects move independently unless they meet in space and time), gravity (objects move downward in the absence of support), and inertia (objects do not change their motion abruptly in the absence of obstacles).¹

In order to study infants’ physical knowledge, Piaget focused on experimental tasks with two characteristics. First, his tasks require deliberate, coordinated action on the part of children. Second, his tasks require that children represent aspects of the world that are not currently manifest to their sensory systems and that they act on such representations to discover aspects of the world that they have never perceived directly. Physical knowledge is revealed, Piaget reasoned, only when children confront problems that cannot be solved by engaging in habitual actions or by responding to perceptible properties of events. The task that best exemplifies both requirements is the invisible displacement object search task, in which an object is moved from view and then undergoes some further, hidden motion. The child’s task is to search for the object by engaging in novel actions on the objects that conceal it. To search successfully, moreover, the child must deduce the object’s location by drawing on knowledge of physical constraints on object motion.

In Piaget’s experiments, 18-month-old infants were found to search for hidden objects by reaching only to positions that are consistent with constraints on object motion. In contrast, younger infants were found to violate all constraints on object motion when they were presented with invisible displacement tasks in which superficial aspects of the situation and habitual actions favored search at an impossible location. These findings suggested that a true appreciation of physical constraints on object motion develops at the end of infancy.

In recent years, Piaget’s conclusions have been questioned, because of the observations on which they depend. Many investigations provide evidence that capacities to act in a coordinated manner are not constant over the infancy period (Diamond, this volume; Wellman, Cross, & Bartsch, 1986). Indeed, Piaget’s own studies (1952) suggest that action capacities undergo extensive changes from birth to 18 months. If that is true, then tasks requiring coordinated search activity are not appropriate means to investigate young infants’ physical reasoning. Rather, studies of young infants require tasks within the infants’ behavioral repertoire. The challenge is to devise tasks that meet this requirement without sacrificing what is essential to Piaget’s experiments: The tasks must not be solvable by engaging in habitual actions or by responding to superficial properties of events.

These requirements were first met, I believe, by experiments by Leslie (e.g., 1984) and Baillargeon (e.g., 1987a). Their experiments investigated infants’ physical knowledge by means of a method that relies on infants’ tendency to look less and less at increasingly familiar events and to look longer at novel events. This method centers on a behavior—looking time—and behavioral patterns—habituation and novelty preference—that are present and functional from birth (Friedman, 1972; Slater, Morison, & Rose, 1984) to adulthood (Spelke, Breinlinger, Macomber, Turner, & Keller, 1990). Thus, the method appears to be appropriate for studies of the cognitive capacities of infants of all ages. To investigate infants’ physical knowledge, Leslie and Baillargeon adapted the method in different ways.

Leslie’s research has focused on infants’ apprehension of causal relationships between objects, in accord with the constraint of no action at a distance. Leslie investigated 6-month-old infants’ sensitivity to this constraint by first habituating separate groups of infants to events in which changes in the motions of two objects coincided or failed to coincide in space and time. Then infants were presented with the mirror reversal of an event. If infants do not perceive causal relations among object motions, Leslie reasoned, then the reversals of both types of events should appear equally novel. If infants perceive causal relations among object motions in accord with the principle of no action at a distance, in contrast, then the reversal of the event in which the objects came into contact should be seen as more novel than the reversals of the other events, because it presented a reversal of causal relations. In the causal event he studied, one object (A) caused a second object (B) to begin moving, and B caused A to stop moving, whereas in the reversal of that event, A caused B to stop moving, and B caused A to begin moving.² Leslie’s experiments provided evidence that infants apprehended the causal relations, in accord with the principle of no action at a distance. Further investigations, using other variants of the preferential looking method, have corroborated this finding (Ball, 1973; Leslie, 1988), although a few negative results have also been obtained (Leslie, 1988; Oakes & Cohen, 1990).

Baillargeon’s research focused on infants’ representations of hidden objects. Her studies (Baillargeon, Spelke, & Wasserman, 1985; Baillargeon, 1987a, 1987b), investigated whether infants represent the existence, location, orientation, shape, and rigidity of an object that stands behind an occluder. The critical events of her experiments presented a stationary object that disappeared behind a moving screen. The screen either stopped moving when it reached the location of the hidden object or it continued moving through that location, revealing empty space where all or part of the object had stood. These events were preceded by a familiarization period in which the screen appeared on an empty stage and moved as in the latter, impossible event.

Looking times to the two critical events were measured and compared. If infants represen...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Dedication
• Table of Contents
• Preface
• Acknowledgments
• I BIOLOGICAL CONTRIBUTIONS TO COGNITION
• II INNATE KNOWLEDGE AND BEYOND
• Author Index
• Subject Index