ABSTRACT
In this chapter I argue that classically conditioned behaviors occurring between the onset of the conditioned stimulus (CS) and the onset of the unconditioned stimulus (US) may be divided into two categories of responses, on the basis of their temporal proximity and their degree of dependence on one or another of these stimuli. Responses of the first category appear as backward-directed (BD): They are primarily elicited by the CS, which is endowed with additional properties as a result of its pairing with the US. BD responses tend to emerge early in the conditioning process and are not highly sensitive to the accurate timing of events. Conceivably, their occurrence is linked to the transfer to the CS, either of the significant value (inducing an enhancement of the orienting reaction to the CS), or of the hedonic or affective value, of the US.
Responses of the second category appear as anticipatory and forward-directed (FD) in nature. FD responses occur late in the conditioning process, and their occurrence is subordinate to specified values of the CS-US intervals. They require cognitive-analytic activities and seem closely linked to the expectancy of the impending US.
An integrative and functional analysis of both types of responses is proposed in which it is suggested that only FD responses subserve a preparatory function for the receipt of the US by the organism.
