Timing or Counting? Control by Contingency Reversals at Fixed Times or Numbers of Responses

Behavior may come under the control of time or number when such cues predict food availability, but time tends to exert stronger control than does number. We asked how the control of behavior is divided between time and number in a procedure where the likely location of a reinforcer reversed systematically at a particular point in a trial. In Phase 1, we asked whether pigeons would choose to time or count when both time and number of responses could be used to discriminate the occurrence of the reversal. Pigeons preferred to time, even when numbers of events were more reliable predictors of reinforcer availability. In the Phase 2, we asked whether control could be shifted from time to number when number was highly discriminable and time was a highly unreliable predictor of the reversal. In this phase, pigeons continued to favor time over number. These findings suggest divided stimulus control between time and numbers depends both on recent experience with relative reinforcer rates and on factors relating to the animal's longer term history, such as training. This research adds to a growing body of work demonstrating strong control by elapsed time when elapsed time is not the most reliable predictor of reinforcer availability.