June 21, 15.50-16.20: Luke Holmes, University of Essex
Pupil Dilation as a Measure of Sexual Arousal
Background: Pupil dilation to explicit sexual stimuli (footage of naked and aroused men or women) appears to be a valid indicator of sexual arousal, because responses reflect sex differences and sexual orientation differences previously described with the (more invasive) measure of genital arousal. However, viewing explicit sexual stimuli can be invasive in itself and limit researchers in recruiting a diverse range of participants. If previous patterns of results were replicated with non-explicit sexual stimuli (footage of dressed men and women), then pupil dilation could be indicative of automatic sexual response in fully non-invasive designs.
Hypotheses: Based on previous literature on both genital arousal and pupil dilation we expect the following patterns, if pupil dilation to non-explicit sexual stimuli is a valid indicator of sexual response: 1. Pupil dilation to explicit sexual stimuli depicting males or females will relate to pupil dilation to corresponding non-explicit sexual stimuli. 2. For both explicit and non-explicit sexual stimuli, the correspondence of pupil dilation to male or female sexual stimuli with self-reported sexual orientation will be stronger in men than women. 3. For both explicit and non-explicit sexual stimuli, the concordance of pupil dilation to sexual stimuli with time spent viewing these stimuli, and self-reported sexual attraction to these stimuli, will be stronger in men than women. 4. For both types of stimuli, the relationships of pupil dilation with self-reported sexual orientation, viewing time, and self-reported sexual attraction to stimuli will be significant, although effects will be stronger for explicit stimuli than non-explicit stimuli.
Method: Participants were 165 men and 160 women of different sexual orientations whose pupil dilation and viewing time were measured with an SR Research infrared eye tracker. Sexually explicit stimuli were 24 videos depicting either a male or a female model masturbating; non-explicit stimuli were 24 videos of a clothed male or female discussing the weather. Videos were 30 seconds long. For the assessment of pupil dilation, participants watched videos before answering three questions regarding their sexual attraction to the depicted person. For the assessment of viewing time, and for each stimulus type (explicit or non-explicit) participants viewed a male stimulus next to a female stimulus, and the time viewing one over the other was recorded. Correlations and linear regression analyses were conducted to test hypotheses.
Results: 1. Dilation patterns to non-explicit stimuli modestly but significantly resembled those to explicit stimuli depicting the same sex or other sex. 2. With explicit stimuli, sexual orientation differences in pupil dilation were significantly larger in men than in women. However, with non-explicit stimuli, this pattern was not confirmed. 3. For both types of stimuli, correlations between pupil dilation, viewing time, and self-reported sexual attraction were significantly stronger in men than women. 4. In general, correlations between pupil dilation and other responses to stimuli were stronger for explicit stimuli than non-explicit stimuli, although they were significant for both types of stimuli.
Conclusions: Pupil dilation patterns to explicit and non-explicit sexual stimuli were modestly related, and most (but not all) predicted sex differences and sexual orientation differences were detected with both types of stimuli. Overall, the present data support the proposal that the assessment of pupil dilation can be combined with non-explicit stimuli for non-invasive studies on sexual attraction and arousal. In several traditional cultures it is impossible to assess genital arousal or to show sexually explicit footage. Thus, the advent of mobile eye trackers, in combination with non-explicit sexual stimuli, shall allow assessing sexual responses in these cultures in a non-offensive manner.
Funding Sources: American Institute of Bisexuality, US Department of Agriculture