Reinforcement-induced within-trial resetting of an internal clock

Rats were trained on a modified peak-interval timing procedure in which three response levers were individually associated with different criterion durations (10, 30 and 90 s) following the onset of a tone stimulus. Delivery of response-dependent reinforcement for each duration was independent of both the responding and the delivery of reinforcement for the other durations, such that the tone stimulus stayed on during food delivery, and no change in the primed reinforcement times occurred. We report here that the delivery of reinforcement at an earlier criterion duration produces a rightward shift in the temporal response functions for later durations by the amount of time that has already elapsed in the trial. This reset in temporal accumulation produces large discrepancies between the programmed and expected (peak) times of reinforcement and suggests that rats are unable to make conditional reinforcement-based discriminations of interval duration. (C) 1999 Elsevier Science B.V. All rights reserved.