The effects of a gap and positive and negative concurrent task events on peak time in the peak-interval procedure

The effect of reinforcement history of a concurrent task cue on pigeons' timing behavior was evaluated using a peak interval procedure. Pigeons were trained to peck a side key on a peak interval procedure. Then separate discrimination training established one center-key light cue as an S+ and another as S-. During the test phase, the S+, S-, and gap (brief termination of the timing side-key light) events were presented at three different temporal locations within sessions, and the effect of each cue on responding to the side key on probe trials was assessed. Peak times under the S+ condition exceeded those under the S- and gap conditions in all three locations and peak times under the gap condition occurred later than those under the S- condition. Peak times under the S+ condition exceeded values predicted by stop and reset clock mechanisms; peak times under the gap condition fell between stop and reset predictions; peak times under the S- condition tended to be lower than values predicted by the stop mode. In a subsequent phase, the extinction of the S+ cue resulted in shortened peak times. In a final phase, the reinforcement of the S+ cue again produced substantially later peak times for that cue. The results suggest that the history of reinforcement is a critical determinant of the effect of a concurrent task cue on timing performance. A combination of delay in resumption of timing following the S+ cue presentation, and clock reset at the end of the task cue is suggested as mediating peak shift observed on concurrent task trials.