Animal memory: the contribution of generalization decrement to delayed conditional discrimination retention functions.

Delayed conditional discriminations in which a sample indicates which comparison stimulus is correct have typically been used in working memory research with animals. Following acquisition with no (0-sec) delay between the offset of the sample and the onset of the comparison stimuli, delays of variable duration are introduced. The resulting retention functions are taken as a measure of memory. We suggest that, in addition to memory loss due to the delay, the comparison of matching accuracy at the 0-sec training delay with relatively novel test delays may produce a generalization decrement that varies as a function of increasing delay. We tested this hypothesis by training pigeons with a mixed delay procedure from the start and found that the retention functions for these pigeons were significantly shallower than those for a control group trained with 0-sec delays and tested with longer delays, and, although reduced in magnitude, the differences persisted for as many as 15 sessions. We propose that a measure of animals' working memory can be obtained uninfluenced by a generalization decrement if they have received comparable training with all of the delays that are tested.