Induced awareness of stimulus differences impedes the generalization of extinction learning with various, highly similar stimuli

Fear extinction procedures serve as a laboratory model for a learning process involved in exposure treatment for anxiety disorders. Clinically, exposure is typically conducted with generalization stimuli (GSs) because originally acquired fear stimuli are inaccessible. Experimental studies, however, show limited generalization of extinction when GSs are used in extinction training (i.e., GS extinction). Stimulus variability may overcome limited extinction generalization. In a first study, we examined whether using multiple, perceptually similar GSs during fear extinction may overcome limited GS extinction generalization. A healthy sample (N = 120) underwent a two-day fear conditioning procedure, with three groups receiving extinction training with a single GS, multiple GSs or the original CS+. Surprisingly, no group differences appeared. Missing awareness of stimuli differences may explain these findings. Hence, in a second study, we aimed to manipulate awareness of stimulus differences between two groups (N = 80), using additional instructions and tasks. Results suggest that enhanced stimulus differentiation was successfully induced, and pivotally influenced extinction learning and generalization. Specifically, greater awareness of stimulus differences resulted in limited GS extinction generalization toward the original CS+. Results highlight a pivotal role of stimulus differentiation, presumably in interaction with attentional and higher-order cognitive processes, for GS extinction learning and its generalization.