The inhibitory effect of pretrial reinforcement on instrumental conditioning.

It has been shown previously that pretrial feeding retards acquisition of an instrumental response. The present experiment tested three hypotheses for this effect: priming, overshadowing and conditioned inhibition. Rats were trained in a runway task with a partial schedule of food reinforcement. Rats that were prefed immediately prior to rewarded trials showed a decrement in acquisition when compared with subjects prefed 180 seconds pretrial. Other subjects prefed immediately prior to nonrewarded trials showed a similar decrement in acquisition, even though the pretrial and goal reinforcers occurred on separate trials. Thus, the adverse effects of prefeeding occurred in the absence of conditions necessary for priming or overshadowing to occur. The results suggest there may be an inhibitory aftereffect of food rewards which can become conditioned to subsequent stimuli.