Karl H. Pribram Stanford University
Experimental analyses of the learning process have developed into two rather different approaches. One, carried out by biologically oriented scientists, seeks to establish the locus of plasticity, and the nature of the more or less permanent changes which allow an accumulation of experience to alter behavior. The other engages computer-oriented scientists and experimental psychologists using human subjects. It focuses on the nature of processes of retrieval: Questions are asked regarding the span which can handle a store, the types of accessing which make available that which is stored, and the structures of the accessing processes. Both of these approaches are based on a model in which the memory store associates spatio-temporally contiguous experiences and accumulates the residues of such associations which then become accessible when some similar experience addresses the storage locus.
This associative model, while valuable in the analyses of simpler forms of learning such as classical and instrumental (operant) conditioning, may not encompass problems encountered when the learning of cognitive processes is involved. Nor does the associative model, as it is currently conceived, allow for the likely possibility that the memory mechanisms of the brain are content rather than location addressable.
A content addressable cognitive learning process involves coding the residues of experience in such a way that subsequent experience automatically addresses the residue on the basis of similarity rather than on the basis of location. Whereas a location addressable process traverses the same paths during acquisition and retrieval, a content addressable process operates somewhat more independently of specific pathways. Mailing a letter uses a location-addressable mechanism; broadcasting a television program utilizes a degenerate form of content addressability (the content is encoded on a carrier frequency).
The work reported here suggests that the cognitive operations of the primate brain are essentially coding operations which "label" the residues of experience so as to make them readily retrievable. In such a scheme, classification of learning processes ought, at some level, to mirror the classification of retrieval mechanisms. Thus, the evidence from experiments involving the primate forebrain, which makes up the bulk of this chapter, should overlap and be congruent with that obtained from the approaches used in memory research involving humans. But at the same