Penile responses of rapists and nonrapists to rape stimuli involving physical violence or humiliation

The sexual arousal profile of a subgroup of rapists with a history of low-level physical violence during their offenses was assessed. Twenty subjects participated: 10 rapists and 10 nonrapists. Stimuli consisted of audiotapes with the following five thematic contents: mutually consenting sexual activities; rape involving physical violence; rape involving humiliation; physical aggression without sexual activities; neutral. Penile responses were recorded during stimuli presentation using a mercury-in-rubber strain gauge. Data showed no differences between both groups for the rape stimuli involving physical violence. For the rape stimuli involving humiliation, however, the penile responses of the two groups differed. With those stimuli the average penile response of the rapists was higher than that of the nonrapists. Therefore, for this subgroup of rapists the association between sexual activities and humiliation presents a higher erotic value than the association between sexual activities and physical violence. Implication of these results as to the discriminant validity and classificatory accuracy of phallometry in rapists is discussed.