The Effect of Extinction Training With Unpaired <scp>US</scp> and <scp>US</scp> Only Presentations on the Contextual Renewal of Human Fear Conditioning

ABSTRACT Past research has shown that contextual renewal of conditional fear can be reduced if unconditional stimuli (USs) are presented unpaired with the conditional stimuli (CSs) during extinction training. The current study examined whether this reduction is a product of strengthened extinction learning from the unpaired presentation of the stimuli that had been paired during acquisition or from habituation to the US. Three groups of participants completed extinction training in a novel context with either: (1) CSs only (CS alone), (2) CSs and unpaired USs (unpaired), or (3) USs only (US alone) presentations. Based on past literature, contextual renewal of electrodermal responses was expected to occur in the CS alone group and renewal of US expectancy in the CS alone and US alone groups. Renewal was absent in electrodermal responses across all groups, limiting interpretation. US expectancy renewal emerged in the CS alone and US alone groups but not in the unpaired group, due to an unexpected increase in US expectancy during CS− in the unpaired extinction phase. This increase, along with parallel changes in affective ratings, suggests that the unpaired group perceived both CS+ and CS− as paired with the US. Taken together, the current findings provided limited support for the effectiveness of unpaired extinction in reducing the return of fear and highlight the role of participants' subjective interpretation of events. US alone extinction showed limited effectiveness, likely due to the high number of US presentations, with some evidence of US habituation.