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International Academy of Sex Research Presentations

Response Specificity and Construct Validity of the Labial Thermistor as Compared with the Vaginal Photoplethysmograph

Prause, N. 1,2, Payne, K. 3, Heiman, J. 1,2, 1Department of Psychological and Brain Sciences, 1101 E 10 th St., Indiana University, Bloomington, Indiana 47405 USA; 2The Kinsey Institute for Research in Sex, Gender, and Reproduction, 313 Morrison Hall, Indiana University, Bloomington, Indiana, 47405; 3Centre for Psychological Services, University of Ottawa, 11, Marie-Curie Street, 6 th Floor, Ottawa, Ontario (email: nprause@indiana.edu)

The vaginal photoplethysmograph has been the most commonly used measure of female sexual arousal. While its response specificity and construct validity have been empirically supported (Laan, Everaerd, & Evers, 1995; Prause, Cerny, & Janssen, 2005), its relative-unit scale renders it unsuitable for between-participant comparisons in smaller sample sizes.

An alternative measure of female sexual arousal that provides an absolute scale of measurement is the labial thermistor. This device consists of a small metal clasp that is padded on one side and has a small, sensitive thermistor on the other. It is designed to measure temperature changes on the medial area of the inner labium. There are limited data, however, investigating the response specificity and construct validity of the labial thermistor.

In this study, 12 women placed the vaginal photoplethysmograph and labial thermistor, which were recorded simultaneously. Participants attempted to place the instruments themselves first, following instructions from the female experimenter. They then continuously indicated how sexually aroused they felt using a pressure-graded lever during three different videos. The videos were selected (through pilot testing) to evoke general arousal, high sexual arousal, or low sexual arousal. At the conclusion of the study, participants completed a series of exercises to test the robustness of both genital measurement instruments against movement artifacts.

The results offer the first empirical support of the response specificity of the labial thermistor by demonstrating that labial temperature increases during sexual stimuli, but does not increase in response to a generally arousing stimulus. The data also replicate previous work supporting the specificity of the vaginal photoplethysmograph. Furthermore, using within-participant continuous 10 s epoched scales, the labial thermistor was correlated more highly with reported sexual arousal as compared to the vaginal photoplethysmograph. The labial thermistor was particularly difficult for women to place without the experimenter’s assistance. Both instruments frequently failed to return to their baseline levels, although it is unclear if this is an instrumentation problem or a true physiological process. Ongoing research is exploring the (1) ability of the labial thermistor to predict between-participant differences and (2) the utility of a fan to return the labial thermistor to baseline response levels between conditions.


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