Trial spacing during extinction: the role of context-US associations.

Studies of extinction in Pavlovian preparations can identify conditions that make extinction more enduring and increase the benefits of exposure-based behavior therapy. One such potential condition is the use of spaced extinction trials. Nevertheless, contradictory results of spacing extinction trials are found in the existing literature. Here we examine the strength of the association between the extinction context and the unconditioned stimulus as a variable that reconciles the seemingly contradictory prior reports. To assess the role of this variable, we evaluated the effects of extinction trial spacing as a function of the associative status of the extinction context in three lick suppression experiments with rats. In Experiment 1, the associative status of the extinction context was manipulated by giving extinction treatment in either the same context as acquisition or a different context. In Experiment 2, the associative status of the extinction context was initially high as a result of the acquisition context being used for extinction and then it was manipulated through postacquisition context exposure. In Experiment 3, extinction was administered in a context different from that of acquisition and the associative status of the extinction context was manipulated by delivering unsignaled footshock (i.e., the unconditioned stimuli) in the extinction context between acquisition and extinction. In all three experiments, consistently less conditioned suppression was observed with spaced extinction trials relative to massed extinction trials when the associative value of the extinction context was relatively low. In contrast, massed extinction trials produced less conditioned suppression when the associative status of the extinction context was high. Thus, stimulus control after extinction is influenced by an interaction between the intertrial interval during extinction and the associative status of the extinction context.