The effect of implicit exposure on fear extinction

Abstract

The current study aimed to examine the effect of implicit exposure on fear extinction learning and return of fear and compared it with that of explicit exposure. Thirty-six participants with no history of psychiatric or neurological illness were recruited to undergo three stages of a fear conditioning experiment, namely acquisition, extinction, and re-extinction. During Acquisition, four geometric shapes served as visual stimuli and two of them were associated with an unpleasant screaming (unconditioned stimulus, US) to become conditioned stimuli (CS+) while the remaining two served as corresponding control stimuli (CS-). During Extinction, participants underwent extinction training in which all CS were presented without the US. One CS+ and one CS- were administered with the use of the continuous flash suppression (CFS), thereby limiting the conscious awareness of these stimuli. The remaining CS+ and CS- were seen with full conscious awareness. During Re-extinction, the US was presented again to evoke the reinstatement of fear, followed by re-extinction in which all the CS were presented without the US. Skin conductance responses (SCR) and subjective aversiveness ratings were recorded at each stage to capture the level of fear responses towards all the CS. The results showed that both subjective ratings and SCR towards CSexp+ and CSimp+ were modulated after extinction, regardless of whether it was presented with the CFS during extinction. No significant reinstatement of fear was demonstrated and the level of ratings and SCR during re-extinction resembled that of extinction. Our findings supported that conscious awareness might not be required for extinction learning to take place. Potential theoretical and clinical implications are discussed.