Parallel Distributed Processing: Explorations in the Microstructures of Cognition

1. Very rarely, a book is published which not only advances our knowledge of a particular topic, but fundamentally recasts our methods of investigating and thinking about large tracts of the map of learning. Linguists remember 1957 as the publication year of Noam Chomsky's Syntactic structures-a book whose ostensible subjects were the structure of English grammatical rules and the goals of grammatical description, but which can be seen with hindsight as the first shot in an intellectual revolution which ended by radically changing the texture of day-to-day research activity and discourse throughout almost all of linguistics, and in substantial parts of other cognition-related disciplines. In decades to come, perhaps 1986 will be remembered by academics as the year of publication of the pair of volumes reviewed here: they constitute the first large-scale public statement of an intellectual paradigm fully as revolutionary as the generative paradigm ever was (there have been scattered journal articles in the preceding four or five years). I would go further and suggest that, if the promises of this book can be redeemed, the contrast in linguistics and neighboring disciplines between the 1990's and the 1970's will be significantly greater than the contrast between the 1970's and the 1950's. (I need hardly add, of course, that it is one thing to fire an opening salvo, but another to achieve ultimate predominance.) The new paradigm is called Parallel Distributed Processing by the sixteen writers who contributed to this book, many of whom work either at the University of California, San Diego, or at Carnegie-Mellon University in Pittsburgh. Some other researchers (e.g. Feldman 1985) use the term 'connectionism' for the same concept. These two volumes comprise 26 chapters which, among them, (i) explain the over-all nature and aims of PDP/connectionist models, (ii) define a family of specific variants of the general paradigm, and (iii) exemplify it by describing experiments in which PDP models were used to simulate human performance in various cognitive domains. The experiments, inevitably, treat their respective domains in a simplified, schematic way by comparison with the endless complexity found in any real-life cognitive area; but simplification in this case does not mean trivialization. There are also auxiliary chapters on relevant related topics; thus Chap. 9, by M. I. JORDAN, is a tutorial on linear algebra, a branch of mathematics having special significance for the PDP paradigm. (Each chapter is attributed to a particular author or