A temporal intermediate stimulus problem

Pigeons discriminated the serial position of a target duration among a sequence of 3 stimulus durations; the specific duration sequences changed across trials. In different conditions, the target duration was the shortest, intermediate, or longest duration in the sequence. Conditions involved a series of transitions in which new duration sequences were added to the stimulus set, providing an assessment of transfer. Pigeons learned and transferred the discrimination when the target was the shortest or longest duration. When, however, the target was the intermediate duration, the birds had great difficulty learning the task and exhibited little transfer to novel sequences. These findings are similar to those observed with nontemporal stimuli in a classic discrimination task, the intermediate stimulus problem. They provide an extension of work on relational timing to a more complex situation.