ABSTRACT
From the very earliest days of Pavlov's investigations of classical conditioning, it has been known that the conditioning process involves considerably more than the basic finding that a previously indifferent conditioned stimulus (CS) becomes an effective elicitor of learned responses following so me number of appropriately paired presentations with an originally effective unconditioned stimulus (US). N otwithstanding the enormous biological significance of the initial conditioned association, in Pavlov's view it was only the opening movement in a subtle and dynamic interplay of excitatory and inhibitory mechanisms by means of which, " ... a continuous and most exact adaptation of the organism to its environment is effected" (Pavlov, 1927, p. 106).
