Blocking of Occasion Setting in Feature-Positive Discriminations

In two experiments rats received feature-positive discrimination training in which brief conditioned stimuli (CSs) were paired with food during presentations of an extended feature stimulus, and non-reinforced in its absence. In Experiment 1 a novel feature was trained in compound with a second, pretrained feature. Acquisition of control over responding to the CS by the novel feature was blocked if the pretrained feature had also been trained in a feature-positive discrimination, compared to a group for whom the pretrained feature had been accompanied by uncorrelated presentations of CSs and food. Experiment 2 employed a within-subjects design. It demonstrated that the feature from a feature-positive discrimination with a particular CS, x, blocked acquisition of control by an added, novel feature over responding to x, compared to the control acquired by the same novel feature over a novel, CS y.