The dissociation of discriminative and conditioned reinforcing functions of stimuli with changes in deprivation.

Pigeons were studied in two experiments designed to explore the effects of deprivation level upon responding in each link of a two-link chained schedule. The stimulus associated with the terminal link of the chain can be both a discriminative stimulus (S(D)) for responding in the presence of the stimulus and a conditioned reinforcer (S(r)) for responding in the preceding link. Previous findings have indicated that the S(r) function was more readily weakened by satiation than was the S(D) function, i.e., the rate of responding decreased more rapidly in the initial link of the chain than in the terminal link. The first of the present experiments, in which tests were conducted after a series of sessions, produced different results: rates of responding in the two links declined simultaneously. The second experiment supported the hypothesis that the effects of satiation interact with the duration of maintenance on the satiation procedure: in early sessions the S(r) function was more readily disrupted, but in later sessions the rates of responding in the two links declined simultaneously. Subsequent to this extensive series of identical sessions, the pigeons' deprivation level was altered before a session by pre-feeding the pigeons up to their normal post-session weights. The rates of responding failed to reflect fully this change in deprivation in the first such session, suggesting that the pigeons' behavior had become partially independent of deprivation level.