Differential inhibition using contextual stimuli.

The present experiments examined whether external contextual stimuli can acquire inhibitory properties through a simple differential context-reinforcement procedure. Rats first received discrimination training sessions in which an electric footshock was consistently delivered in one context, but not in a second, different context. In Experiments 1A and 1B, summation and retardation tests were subsequently performed using the non-reinforced context. Each of these tests failed to reveal contextual conditioned inhibition. In Experiment 2, a summation and retardation test were performed using a contextual stimulus that was unique to the non-reinforced context. Weak but significant contextual inhibition was found. It was suggested that contextual stimuli that are unique to the non-reinforced context did acquire inhibitory strength in each experiment, but that in Experiments 1A and 1B, expression of this inhibition during testing had been masked by the concurrent presence of excitation from elements that the non-reinforced context had in common with the reinforced context.