Second-order conditioning with and without unconditioned stimulus presentation

Examined the effects of presenting various episodes after serial presentation of 2 CS (CS2-CS1 sequences) on 2nd-order conditioning to CS2 in 3 experiments using 88 male Sprague-Dawley rats in an appetitive conditioning situation. In Exp I, presentation of food UCS immediately after CS2-CS1 sequences interfered with 2nd-order conditioning of CS2. In Exp II, postsequence presentation of a "surprising" UCS interfered with 2nd-order conditioning more than did presentation of an "expected" UCS; similarly, less 2nd-order conditioning of CS2 was observed when postsequence nonpresentation of a UCS was surprising than when UCS omission was expected. In Exp III, the interfering effect of UCS presentation on 2nd-order conditioning was smaller when a brief delay was introduced between presentation of the CS2-CS1 sequence and the UCS. (19 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved).