The relationship between similarity judgments and psychophysiological responsivity

The relationship between stimulus similarity and psychophysiological responsivity was investigated using the information detection paradigm. The study focused on two major issues: (1) the relationship between the Skin Conductance Response (SCR) to a stimulus and its perceived similarity to a relevant stimulus; (2) the possibility of using a psychophysiological measure (SCR), in addition to similarity judgments, to differentiate between two models of similarity. Tversky's (1977) contrast model, which assumes that similarity between stimuli is determined by their common and distinctive features, was compared to the geometrical model of similarity. Each of 64 subjects chose one out of four geometrical forms. The subjects were then presented with a sequence of ten stimuli with a different degree of similarity to the chosen (relevant) stimulus. SCRs were recorded during stimulus presentation. At the end of the stimulus sequence the subjects judged the similarity between all possible pairs of stimuli. A significant relationship between the perceived similarity and the SCRs was obtained. Both the contrast and the geometrical models were found to be able to account for the pattern of responses, with an advantage to the former. However, this advantage was clear and significant only when judgments were used; the physiological measure was not sufficiently sensitive to discriminate between models that are relatively close. The implications of the relationship between perceived similarity and electrodermal responsivity were discussed.