ASSOCIATIVE STRUCTURES UNDERLYING ENHANCED NEGATIVE SUMMATION FOLLOWING OPERATIONAL EXTINCTION OF A PAVLOVIAN INHIBITOR

Two experiments used lick suppression by water-deprived rats to investigate the associative structure underlying the enhancement of negative summation often seen following operational extinction (i.e., X-) of a Pavlovian conditioned inhibitor ( A+ AX-). Our expectation was that one consequence of inhibitory training with Stimulus X was X's accruing excitatory strength through mediation by Stimulus A, and that operational extinction of A attenuated this strength. Experiment 1 determined that, following A+ AX- training, operational extinction of X enhanced negative summation even when the same excitor was used both on the summation test and in inhibitory training (i.e., Stimulus A). This suggests that the enhanced negative summation arises from extinction of a direct X→US excitatory association, which is mediated by A during acquisition but not during subsequent retention. In Experiment 2, the AX compound was extinguished following A+ AX- training. This treatment was intended to maintain the X→A association while extinguishing the X→US association. Stimulus X was then tested in summation with an excitor other than A. Unlike extinction of X alone, extinction of AX caused no increase in the inhibitory potential of X; however, it produced a decrease in the excitatory value of A. Additionally, Experiment 2 found that the effectiveness of further inhibition training was similar to operational extinction of X in increasing X's inhibitory response potential. These results are consistent with the view that X, as a result of the AX- trials of inhibitory training, comes to possess a direct X→US associative link, and that the negative summation potential of an inhibitor is a function of the discrepancy in excitatory associative strengths between the putative inhibitor and the conditioned excitor used in inhibition training. © 1992.