SIMULTANEOUS CONDITIONING DEMONSTRATED IN 2ND-ORDER CONDITIONING - EVIDENCE FOR SIMILAR ASSOCIATIVE STRUCTURE IN FORWARD AND SIMULTANEOUS CONDITIONING

A second-order conditioning procedure was used to evaluate the associative consequences of forward versus simultaneous pairings of the first-order CS and US with water-deprived rats as subjects in a conditioned lick suppression task. In Phase 1, a tone was presented in a forward, simultaneous, or explicitly unpaired relationship to shock. In order to assess what was learned in Phase 1, all animals in Phase 2 were exposed to clicks in a forward relationship to the tone. In order to determine the mediational role of the tone in promoting conditioned responding to the clicks, in Phase 3 the first-order tone was extinguished for some animals and not extinguished for others. A test for conditioned lick suppression to the first-order tone found responding to be superior in the subjects that received the tone and shock in a forward arrangement relative to subjects that experienced the tone and shock in a simultaneous arrangement. However, a test for suppression to the second-order clicks revealed substantial and equal fear of the clicks in those groups which were exposed to either forward or simultaneous tone-shock pairings in Phase 1, followed in both cases by forward click-tone pairings in Phase 2. These results indicate that temporal contiguity is a sufficient condition for the establishment of an association; however, a forward temporal relationship between stimuli (e.g., clicks → tone) appears necessary for expression of the association appropriate for anticipation of the US. Phase 3 tone extinction did not attenuate the ability of the second-order clicks to control behavior in either the forward or simultaneous case, which suggests that a representation of the first-order tone played no mediational role in behavior controlled by the second-order clicks. The structures of forward and simultaneous associations are compared. © 1991.