CS-US interval as a determinant of the form of Pavlovian appetitive conditioned responses

The effects of variation in temporal and predictive relations between the onset of visual and auditory CSs and delivery of a food UCS on the form of CRs were examined in 4 experiments with 192 male Sprague-Dawley rats. In Exp I, substantially different CRs were evoked by CSs differing in duration and CS-UCS interval in delay conditioning. Using a 2nd-order conditioning technique to assess the associative strength of CSs of different delay intervals, Exp II showed that shorter intervals generated more strength than longer intervals, but the differences in CR form observed in Exp I were not dependent on differences in associative strength. In Exp III, CSs of equal duration but different CS-UCS intervals in trace conditioning evoked CRs similar in form to those observed with delay procedures in Exp I. In Exp IV, the onset of a CS of intermediate CS-UCS interval was made less predictive of UCS delivery by separate nonreinforced short duration presentations of that stimulus. Behavior evoked by the intermediate interval CS was more like that evoked by CSs of longer CS-UCS intervals. These data are discussed in terms of an orienting response hypothesis proposed earlier to account for differences in the nature of CRs evoked by CSs differing in physical characteristics such as modality. (27 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved).