Effects of intertrial reinforcers on rats' timing behavior

Two experiments were conducted to assess the effects of non-contingent intertrial interval (ITI) reinforcers on rats' discrimination of duration. In the first experiment, rats' discrimination of a 2 vs. 8 s of light was significantly disrupted when reinforcers were presented in the ITI. Disruption was not different on short (2 s) and long (8 s) trials. The second experiment showed that this disruptive effect was not specific to trials preceded by ITI reinforcers; responding on empty ITI trials run in the same session as ITI-reinforcer trials was also disrupted. This disruption however was not as great as on the ITI-reinforcer trials. The results of these experiments show that ITI reinforcers affect timing discriminations in much the same way they affect classical conditioning and delayed matching to sample. However, detailed examination of the results suggests that the deleterious effects of ITI reinforcers in these different paradigms might be produced by different rather than the same mechanism. The results also support the conclusion that pre-trial reinforcement "priming" produces disruption rather than facilitation in complex tasks.