Delayed stimulus control: recall for single and relational stimuli.

Researchers taught pigeons two kinds of matching-to-sample tasks. One task used single pictures. The other task used pairs of pictures that had to be treated as a set.

After each match, the birds waited 0, 2, 4, 8, or 16 seconds before they picked the comparison keys. The team then checked how many choices were still correct.

Memory for both kinds of tasks dropped at the same speed as the wait grew longer. But the relational sets started off harder, so accuracy began lower and stayed lower at every delay.

The slope of forgetting did not change. Only the starting point did.

Bernal et al. (1980) saw the same decay curve when pigeons could peck during the delay. Letting the birds move kept scores higher, but the downward slope stayed parallel. Kunz et al. (1982) now shows the slope also stays parallel even when the task itself is harder.

Wilkie et al. (1981) found that extra visual flashes during the wait hurt accuracy. Taken together, the three studies say: delay hurts, extra sights hurt, but task difficulty only sets the launch point, not the fall.

Burgio et al. (1986) later split delay into two parts: time before the choice and time before the food. They showed the first gap matters most. Kunz et al. (1982) fits right in: once the sample is gone, forgetting runs on a clock that task type cannot speed up or slow down.

When you teach conditional discriminations, expect harder relations to start off weaker even though memory decay rates stay the same. Build extra practice trials for tough relations up front. Keep visual clutter away during wait times. And remember: if a learner bombs after a long delay, the fix is usually more pre-training, not a new memory trick.