Context and renewal of conditioned fear: an experimental evaluation using 20% carbon dioxide-enriched air as an unconditioned stimulus.

This analogue experiment used fear conditioning and extinction procedures to establish and reduce fearful responding and then test for fear renewal following a context change. Healthy undergraduates (N=61) underwent a differential fear conditioning procedure using geometric shapes as conditioned stimuli (CS) and inhalations of 20% CO(2)-enriched air as an aversive unconditioned stimulus (US). Across phases (i.e., habituation, acquisition, extinction, and test), red and green ambient lighting served as contextual stimuli, and electrodermal and evaluative ratings were assessed as indices of conditioned fear. The control group underwent extinction and test phases under identical conditions (i.e., no context changes). The experimental groups either underwent acquisition and test phases in one context and the intervening extinction phase in a different context (A-B-A), or underwent acquisition and extinction phases in one context and the test phase in a novel context (A-A-B). Consistent with expectation, fear renewal was observed when the test context matched the acquisition context. This effect was modest for electrodermal responses, but reasonably robust for evaluative responses. The role of context in the subsequent renewal of fear following exposure-based treatment is discussed.