A delay-specific differential outcomes effect in delayed matching to sample.

In delay-specific remembering, accuracy in delayed matching-to-sample tasks is enhanced after single delays or retention intervals relative to performance at other delays. In the differential-outcomes effect (DOE), accuracy is enhanced at all delays when the outcomes of correct choices are quantitatively or qualitatively different, compared to when outcomes are the same. In the present experiments, we aimed to demonstrate a delay-specific DOE by arranging differential outcomes for correct responses at some delays and same outcomes at other delays. In each of two experiments, four pigeons worked in delayed matching-to-sample tasks with delays of 0.5, 5, and 15 s, or 0 s, 3 s, and 12 s mixed within session. Correct choices produced different reward durations (differential outcomes) at one or two delays, or the same reward durations (same outcomes) at the other delays, on a within-session basis. There was evidence of improved accuracy at delays at which differential outcomes were arranged, compared to accuracy at delays at which same outcomes were arranged, that is, a delay-specific DOE. The more usual DOE was confirmed in a third experiment with same outcomes at all delays in one condition and differential outcomes at all delays in another. We discuss implications of a delay-specific DOE for theories of the DOE which attribute the effect to enhanced stimulus control by expectancies of reward outcomes generated at the time of sample presentation.