Memory interval distribution effects in pigeons

Pigeons were trained with two concurrent delayed conditional discriminations that involved different distributions of memory intervals, namely 1 and 5 sec in the “short” and 5 and 10 sec in the “long” distribution. Memory for the initial stimulus was much better after 5 sec in the short distribution than in the long one. The memory functions between the intervals within each distribution were essentially flat. These findings were replicated in a second study that involved differential outcomes; this procedure enhanced memory generally within trials so that memory intervals of 1, 9, and 19 sec could be used, with 9 sec serving as the common memory interval. The findings are interpreted on the basis of the subject’s expectation of the likely duration of the upcoming memory interval and the associated delay of reinforcement.