Using a light (L) as the reinforced CS and a tone (T) as the conditioned inhibitor, rabbits received conditioned inhibition (CI) training of the nictitating membrane response. In Experiment 1, animals were matched in terms of initial acquisition to L and T, using electric shock to the eye as the UCS to form three groups. Group 100 received 100 CI trials per single daily session, Group 200 received 200 CI trials per single daily session, and Group 100/100 received 200 daily trials in two sessions separated by an interval of approximately 3 h. Each unit of 100 trials consisted of 50 reinforced L trials (L+) and 50 nonreinforced L-T compound trials (LT-). The development of suppressed conditioned responding over the course of 1,300 CI trials and the results of a retardation test (T+) failed to detect differences among these three trials-distribution procedures. Experiment 2 examined the development of CI using the two-session/day procedure with intersession intervals of 3 and 6 h. No differences in CI were apparent over the course of 2,000 trials or in the retardation test. These findings suggest robust CI can be obtained with relatively massed training and that theories of CI might minimize the role of distribution of training in their formulations.
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