Dissimulation in phallometric testing of rapists' sexual preferences

Sexual preferences of 38 rapists were assessed phallometrically with and wi thout a semantic tracking task in a counterbalanced design. Four categories of audiotaped vignettes describing neutral interactions, consenting sex, r ape, and nonsexual violence were employed as stimuli. In the semantic track ing task, participants were instructed to press one button when violent eve nts were described in the vignette and another when sexual activities were described. Phallometric assessment with the semantic task better discrimina ted between rapists and non-sex-offender participants (from an earlier stud y) than the same assessment without the task. Among four rapists who had pr evious experience with phallometric testing, there was a very strong correl ation between deviance scores and tracking accuracy. Results suggest that t he semantic task may improve discriminant validity, particularly among sex offenders who have had previous experience with phallometric assessment.