An instrumental partial reinforcement effect in the absence of any overt instrumental acquisition training

Rats were placed directly over a food cup or received ordinary runway trials under either partial or consistent food reward, no other acquisition training having been given. Also included was a group that was nonrewarded on all running trials. A gradient occurred in extinction such that type of acquisition training (placed vs run) exercised less influence over performance and schedule of reward (partial vs continuous) exercised more influence over performance both as extinction training progressed and as the goal section was approached. The results suggest that rats make small terminal instrumental reactions on placement trials, reactions which, if strongly conditioned, can support a partial reinforcement effect in the full instrumental reaction, particularly in the goal area.