The effects of presenting additional stimuli resembling the CS+ during extinction on extinction retention and generalisation to novel stimuli.

Recent studies have shown that extinction training including the conditional stimulus (CS+) and stimuli similar to the CS + enhances extinction retention and generalisation to novel stimuli. The aim of the present study was to confirm that these effects are specific to presenting stimuli similar to the CS+ during extinction and not merely an effect of additional trials or additional stimuli unrelated to the CS+. In an experiment conducted in a single session on the same day, participants (134 adults; 70.7% female; 17-40 years of age, M = 20.04, SD = 4.36) completed a habituation phase followed by an acquisition phase using dog images presented with (CS+) and without (CS-) a dog growl paired with a scream unconditional stimulus (US). Participants were randomly allocated to four extinction conditions: Multiple exemplar extinction comprising the CSs and two novel dog images similar to the CS+; Standard extinction control matched for the number of CS+ and CS- presentations; Extended extinction control matched for the total number extinction trials, and Other stimuli extinction control comprising the CSs and two novel stimuli unrelated to the CS+. All participants completed an extinction test with the original CSs followed by a generalisation test with two novel dog images. Multiple, Standard and Other stimuli extinction groups exhibited larger skin conductance responses (SCRs) during extinction to the CSs compared to the Extended extinction group. SCRs to the additional dog images in the Multiple group were larger than SCRs to the additional CSs in the Extended group and the novel images in the Other stimuli group. There were no group differences in responses to the CSs during extinction test. Unlike the other groups, SCRs to the first presentation of the novel generalisation dogs did not differ from those to the last CS trials in extinction in the Multiple group. However, this group difference did not persist beyond the initial generalisation trial. Finally, the Multiple, Extended, and Other stimuli groups exhibited more negative CS evaluations after extinction, extinction test, and generalisation test than the Standard extinction group. The results suggest that extinction with the original CSs and additional stimuli resembling the CS + elevated physiological responses during extinction and reduced physiological responses to novel stimuli similar to the CSs. Further studies are needed including clinical samples and trial-by-trial evaluations of the stimuli presented.