American Scientist

The Mind's Past. Michael S. Gazzaniga. 216 pp. University of California Press, 1998. $20.

Working scientists who take the time to explain to the general reader what is happening in their field do an invaluable service to science and to the life of the intellect. In the past year, we have benefited from two notable efforts of this kind. First came Steven Pinker's How the Mind Works—lengthy but beautifully written—and now this much shorter, breezily written book by Michael Gazzaniga, a leading researcher and influential editor in cognitive neuroscience. Both books cover a broad range of contemporary research on how the mind works, but Gazzaniga is much more concerned with mind-brain relations than Pinker. Indeed, a central concern of Gazzaniga's is conscious experience and its complex relation to the brain's activity.

Gazzaniga stresses the many findings indicating that most of what the brain does—including most willed action—is done without conscious control. Consciousness is the "awareness we have of our capacities as a species, not the capacities themselves." The capacities themselves depend on myriad different special-purpose circuits, which have evolved as solutions to the many very different information-processing problems that confront the brain, just as the lungs, the kidney, the liver and other distinct organs have evolved as solutions to distinct physiological problems. Consciousness, in Gazzaniga's view, is the product of a few circuits whose function is to interpret our behavior and our emotional responses to environmental challenges. The interpreter represents itself as the source of these responses, but it is not. It is as if the president's press spokesman confounded him or herself with the entire executive branch.

Both Gazzaniga and Pinker debunk the ubiquitous and sociopolitically influential assumption that our brain is a general-purpose organ of intelligence, with almost unlimited plasticity (at least when we are very young). In this view, the brain is a formless neural net—the neurobiological equivalent of the blank slate imagined by the empiricist philosophers. Experience shapes the net into the form that best adapts our behavior to whatever world we happen to find ourselves in. Gazzaniga and Pinker argue that, on the contrary, our brain is a collection of special-purpose organs. Each such organ solves a particular information-processing problem. Its structure has been shaped by natural selection to make it wondrously good at handling that problem and hopelessly ill-suited to handling other problems that have a different informational structure.

In ontogeny, the structures of these organs are largely self-differentiated, to use a term coined by Paul Weiss. Their form arises from a genetically specified developmental program, which produces at least the skeleton of the mature form before the onset of function. Developmental programs presuppose nongenetic (or only indirectly genetic) inputs at every stage of their elaboration. For example, the wiring of the visual projection pathways may depend on endogenous waves of activity that sweep across the retina of the fetus. But, Gazzaniga argues, the important role of these nongenetic inputs to the developmental program should not mislead us into imagining, for example, that the structure of the many different kinds of cortical circuits for processing visual input arise primarily from the formative effect of visual experience acting on an infinitely plastic medium. On the contrary, their basic structure is a consequence of selection pressures from the most enduring features of the world we actually live in, acting over an evolutionary (phylogenetic) rather than an ontogenetic time scale. Together, these myriad special-purpose organs of intelligence enable us to survive in this world, not in some arbitrarily structured world.

The book would have benefited from more extensive editing and fact-checking. It covers a vast range of contemporary and classic research, devoting a few paragraphs or a few pages to succinct descriptions of the work of many well-known researchers in cognitive science and cognitive neuroscience. These breezy capsule presentations are often fine, but sometimes they are incomprehensible (for example, the presentation of Roger Shepard's ideas about stimulus generalization and categorization). Some names are mistaken (Richard Sayfarh for Robert Seyfarth), and the thinking of some classic investigators is mischaracterized. (The ideas imputed to Paul Weiss on function preceding form are the opposite of those he actually held.)

Reading this book is the next best thing to going out for a few beers with Michael Gazzaniga to learn what is happening in cognitive neuroscience. It is the short and easy version of the unusually successful scholarly tome The Cognitive Neurosciences, edited by Gazzaniga, with contributions from most of the leaders in the field. Much of the work in that volume is summarized in this short book, which belongs on the reading list of those who want to know more about cognitive neuroscience.—C. R. Gallistel, Psychology, University of California, Los Angeles