Reductionism, Connectionism, and the Plasticity of Human Consciousness

ion. What is important is that the network have a ’teacher’ of some appropriate sort, a teacher who can help to shape the character of its internal representations and the pattern of its environmental responses. We have seen how relatively simple networks can be trained to recognize complex and culturally-imposed auditory features like mine echoes and phonemes. We have seen how they can learn the highly irregular and highly context-sensitive transformation rules that are essential to the task of reading English text. And we have seen how they can be trained to recognize the endlessly variable 3-D structures of external objects from 2-D grey-scale pictures of them. In each case, the network is forced toward acknowledgement of some feature or domain of features selected from the infinity of possible features to which it might respond, and it is not an insuperable problem that the features at issue are complex, subtle, context-sensitive, or stimulus transcendant. With suitable teaching, the network generates an internal representation of them regardless. This does not mean that the features addressed are magical, or super-physical, or beyond the realm of natural science. It just means that the simplest possible definition or representation of them may well be the entire configuration of the successfully trained network! Given a network of any nontrivial size, those representations can be extraordinarily complex, but it is no part of the reductionist’s program to deny this. It therefore should not be a surprise that a human infant comes to recognize and respond to cultural features that resist definition in terms of notions like mass, charge, length, and so forth, because the most dominant ’teacher’ in the local environment is the culture into which the infant is born. The set of weights that constitutes a child’s developing consciousness is continually being shaped by the linguistic, conceptual, and social surround. The developing brain comes to reflect the elements 43 THE PLASTICITY OF HUMAN CONSCIOUSNESS and structure of that surround in great detail. For that is what networks do. What shapes them is the stimuli they typically receive, and the subsequent corrections in their responses to which they are typically subject. Small wonder we become attuned to the categories of the culture that raises us. This may sound like a major concession to the view that the most important factors in the explanation of human behavior are to be found at the cultural rather than at the microphysical level. But to say this would be to miss the point, and to acquiesce in a false dichotomy between ’cultural’ and ’physical’ features. The real distinction is between features that are simple and context free on the one hand, and features that are extraordinarily complex and have many layers of context dependency on the other. The latter are indeed of major importance for explaining human behavior. But neither they, nor our capacity for recognizing them, is forever beyond a naturalistic understanding. For we can already understand, right here and now, how a system of many simple physical elements can come to represent them, and to respond to them, and to undergo dramatic conceptual development in the process. That is the prospect that a computational neuroscience holds out to us, and I think it would be a tragedy if anti-reductionist convictions should frustrate or slow our pursuit of this prospect. Such conservative convictions, to judge from the preceding discussion, may be based on true and important premises about human nature. But they underestimate the capacity of emerging science to provide a highly revealing and naturalistic explanation of those very same premises. And such explanation, after all, is what scientific reduction amounts to.