American Scientist

The Infant's World. Philippe Rochat. x + 262 pp. Harvard University Press, 2001. $29.95.

Philippe Rochat's The Infant's World is a concise, thoughtful book about the psychological transformations that take place during the first year of life. Framed by the author's own studies on the development of motor control, intermodal perception and social cognition, the book also offers a thorough review of much of recent research on infancy.

Rochat, a psychology professor at Emory University, sees infancy as best understood through the intersection of three domains—the self (one's own body), physical objects and other people. These are the three "inseparable pillars" of infant experience, each initially distinct but soon mutually influential as the child becomes fully integrated into his or her environment. In Rochat's view, which is fundamentally ecological, the infant's mind cannot be understood apart from its environment. But deciphering the infant's niche is no easy task, given the striking changes in sensory function, motor control, language and autonomy between infancy and adulthood. True to his title, Rochat brings us convincingly inside the infant's world, where we see an adaptive situation fundamentally different from our own, demanding cognitive solutions far different from a simple unfolding of adultlike capabilities.

Rochat introduces the book with certain "facts" of research on infancy. Long neglected in psychology as a topic of serious inquiry, the study of infants has blossomed in the past quarter-century, thanks to two strikingly simple advances. The first is improvements in video technology that have permitted researchers to record and analyze infant behavior in objective, microscopic detail. The second (decidedly lower-tech) advance has been the devising of conditioning and dishabituation procedures to coax out the surprisingly sophisticated perceptual and reasoning abilities of preverbal, motorically undeveloped children. Descriptions of such experiments appear throughout the book, providing both empirical support for Rochat's theoretical arguments and moments of lighter reading, as one marvels at the ingenious tricks scientists have invented for probing the infant mind.

Another recurring theme is the ontogeny-phylogeny metaphor, which Rochat credits with launching the serious study of infancy following the Darwinian revolution in the mid–19th century. Although evolutionary biologists cringe at its simplicity, there is something quite compelling in the idea that children follow the same mental trajectory during development that our prehuman ancestors likely traversed during the evolution of our species. From an initial state dominated by motor reflexes and sensory preoccupation with the immediate environment, infants progress to simple intentional and planned actions; this is followed, toward the end of the first year, by a capacity for symbolic reasoning and the dawning of self-awareness.

The ontogeny-phylogeny metaphor is also appealing from a neurological point of view, although this is not a focus of Rochat's book. Brain-stem circuits, which control basic vegetative functions and survival reflexes, mature earlier than primary sensory and motor areas of the cerebral cortex, which in turn mature earlier than higher-order, integrative areas in the frontal, parietal and temporal lobes. When Rochat does turn to the neural mechanisms underlying cognitive development, his comments are a bit off base. Excess neurons in the human brain are pruned well before birth—not after, as Rochat repeatedly states. Nor is it the case that human infants "are born sooner and develop at a slower pace compared to youngsters of any other primate or mammalian species." By most neurological measures, a human newborn is about as well developed as other primate neonates and far more mature than the newborns of altricial mammals such as rats, cats and dogs.

Rochat's emphasis on neonatal helplessness is all the more surprising given his own contribution to the revolution in infant cognition. Throughout the past two decades, researchers have dazzled us with their discoveries about the remarkable competency of young infants: Andrew Meltzoff's demonstration of neonatal imitation; Elizabeth Spelke and Renée Baillargeon's discovery of physical reasoning in three-month-olds; Karen Wynn's revelations about numerosity in five-month-olds; and Rochat's own findings about bodily awareness and the appreciation of social causality in very young infants.

These findings, along with many others, are woven together in the three chapters—on the infant's understanding of self, objects and other people—at the core of the book. Rather than review each topic in comprehensive detail, Rochat uses the three domains to support his view that there are two key transformations in infancy: The first comes at two months of age, when infants show the first signs of intentional exploration and a sense of their own power over their physical and social environment. The second transition is at nine months, when infants begin to appreciate intentionality in others, which helps them cross the threshold into symbolic communication. These are the major landmarks, but Rochat does not ignore other ages. The book is filled with interpretive gems that can only come from one who has spent many years closely observing infant minds at work.

The book concludes with two chapters summarizing the key transitions of infancy and the possible mechanisms by which they come about. Oddly, after so cogently convincing us of the revolutions at two and nine months, Rochat confesses some discomfort with the whole concept of developmental stages. He notes that the evidence for sudden steplike progressions in infant competency tends to come from measures of group averages, whereas individual developmental trajectories are typically quite chaotic. Nonetheless, there is something very appealing—and perhaps useful—in the idea of discrete developmental steps, which is unlikely to disappear simply for lack of empirical or neurobiological support.

The strength of the book lies in its three pillars. Other theorists have tended to pick objects or people as the primary foundation of infant cognition. Rochat gives these two categories equal weight and adds a third, often overlooked but equally important, foundation: the self. Privileged, permanent and present even before birth, the child's own body is both the first source and ultimate repository of a growing knowledge of the world.—Lise Eliot, Neuroscience, The Chicago Medical School