Dissimulation in phallometric testing of rapists' sexual preferences.

Sexual preferences of 38 rapists were assessed phallometrically with and without a semantic tracking task in a counterbalanced design. Four categories of audiotaped vignettes describing neutral interactions, consenting sex, rape, and nonsexual violence were employed as stimuli. In the semantic tracking task, participants were instructed to press one button when violent events were described in the vignette and another when sexual activities were described. Phallometric assessment with the semantic task better discriminated between rapists and non-sex-offender participants (from an earlier study) than the same assessment without the task. Among four rapists who had previous experience with phallometric testing, there was a very strong correlation between deviance scores and tracking accuracy. Results suggest that the semantic task may improve discriminant validity, particularly among sex offenders who have had previous experience with phallometric assessment.