Preparedness and preattentive associative learning: electrodermal conditioning to masked stimuli

We examined whether electrodermal responses can be conditioned to stimuli that are denied access to conscious awareness because of backward masking. An electric shock unconditioned stimulus (US) followed one of two conditioned stimuli (CS+ and CS- respectively). For the critical group of subjects, the CSs were followed by masking stimuli that effectively precluded their conscious recognition. To test for conditioning, the CSs were presented masked and nonreinforced during acquisition test-trials, or nonmasked and nonreinforced during an extinction series. Comparison groups of subjects had a long interval between the CSs and the mask, allowing conscious perception of the CSs, or were given unpaired presentations of the US and the masked CSs, before a nonmasked extinction phase which was identical to that in the conditioning groups. The data consistently demonstrated conditioning effects to effectively masked CSs, but only if the CS+ was fear-relevant. Thus, nonconscious, automatic conditioning effects were obtained to masked angry faces or to masked presentations of spider or snake pictures. No conditioning effects were discernible with masked neutral CS+ (happy faces, flowers, mushrooms). Subjects instructed to rate their US expectancy in the CS-US interval reliably differentiated between the masked CS+ and the masked CS- although the stimuli proved unrecognizable in a concurrent forced choice recognition task. Thus, the subjects were able to discriminate between the nonrecognized masked CSs in their ratings, perhaps through feedback from the conditioned response.