Blocking of the Rabbit's Classically Conditioned Nictitating Membrane Response: Effects of Modifications of Contextual Associative Strength

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The effects of contextual manipulations on the magnitude of discrete cue blocking of the rabbit's nictitating membrane response were investigated in three experiments. Experiment 1 showed that changing or extinguishing the single stimulus training context prior to compound training attenuated the blocking effect. In contrast, extinction of the context following compound conditioning did not attenuate blocking. In Experiment 2, attenuation of blocking was found to be greater following extinction of both the discrete CS and the context, in comparison to extinction of the discrete cue alone. Interpolation of US-alone presentations (context conditioning) between single stimulus training and compound conditioning produced no effects. In Experiment 3, enhanced responding to the blocked stimulus was observed following a retention interval interposed between compound training and testing. However, the blocking effect was preserved if subjects were repeatedly exposed to training context cues during the interval (i.e., context extinction) and tested in the presence of those cues. The results of the present investigation support the conclusion that the CS complex producing the blocking effect is composed of both discrete and contextual components. The observed effects were discussed in terms of associative and comparator models of conditioning.