Common and Distinctive Features of Verbal and Pictorial Stimuli as Determinants of Psychophysiological Responsivity

The present study focuses on the relation between stimulus features and psychophysiological responsivity by using a modified version of the information detection paradigm. Compound pictorial and verbal stimuli (schematic faces with beard, glasses, and hat, and descriptions of people in terms of occupation, city of residence, a hobby, and a personality trait) were used as the relevant stimuli that subjects were instructed to memorize. Skin conductance responses were measured during the subsequent presentation of a sequence of test stimuli. Each sequence included a critical stimulus that shared from one to four common components with the relevant stimulus in each of two pictorial and two verbal experiments. We hypothesized that the electrodermal responsivity to the critical stimulus would reflect the degree it matches the relevant one. The results indicated that when the critical stimulus was identical to the relevant stimulus, responsivity was maximal. Neutral stimuli (i.e., those that shared no components with the relevant stimulus) produced minimal responsivity, and critical stimuli that only partially matched the relevant one produced intermediate levels of responsivity (in spite of the subjects' awareness of the differences between the critical and the relevant stimuli). The monotonic relation between the degree of match and responsivity supports the proposed model, which assumes that each stimulus in the sequence is being compared with the relevant stimulus by a feature-matching process, and electrodermal responsivity is related to the outcome of this process. In a fifth experiment, we compared geometric and contrast models for similarity and found that the pattern of responsivity violated the minimality and symmetry assumptions of the geometric model. The relation between cognitive processes and psychophysiological responsivity is discussed, as are implications for the application of the guilty knowledge technique for detecting information.