Abstract
Using a conditioned suppression paradigm, differential conditioning between short (S, 0.7s) and long (L, 4.9s) US was studied in five groups of rats where the mean intervals between transition (S→L, L→S) and between nontransition (S→S, L→L) were varied across groups. Group ITI-S was trained with the short intervals in either case, while Group ITI-L was with the long intervals. Group Medium was trained with the intermediate intervals in either case. Group Trns-S had the short intervals between transition and the long intervals between non-transition. For Group Trns-L, these relations was just reversed. The greater differentiations were obtained in Groups ITI-L and Trns-L which had the long inter-transitional intervals. The figures of the differentiations were quite similar in two groups which had the same inter-transitional intervals despite of their mean intertrial or nontransitional intervals. These results suggest that the inter-transitional interval rather than intertrial interval plays a critical role for the trial-distribution effects in a differential conditioning of US duration.
