The effects of fading procedures on discrimination shifts.

Human discrimination learning is frequently characterized as a "two-link process" consisting of an instrumental response and a covert dimensional attention or mediation response. In subsequent conceptual shift problems, reversal shift facilitation is attributed to partial reinforcement of the covert response in the original problem. Unlike standard trial and error learning conditions, a fading design eliminated the partial reinforcement of covert responding and, consistent with the hypothesis, reduced reversal shift facilitation. Although fading procedures facilitate discrimination learning, they may retard subsequent trial and error learning, a cost that warrants further exploration. Trial and error conditions produced the expected reversal facilitation.