1. INTRODUCTION Currently, the most widely used method for measuring genital responses in women is the vaginal photoplethysmograph (Sintchak and Geer, 1975). 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. Also, copious movement artifacts are a serious challenge to signal integrity. 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 to measure temperature changes on the other side. We attempted to (1) replicate existing work on the thermistor’s sensitivity to sexual arousal and (2) extend the convergent validity and specificity data on the thermistor by comparing the instruments worn simultaneously during visual stimulation. RESPONSE SPECIFICITY AND CONSTRUCT VALIDITY OF THE LABIAL THERMISTOR AS COMPARED WITH THE VAGINAL PHOTOPLETHYSMOGRAPH Prause, N. 1, 2, Payne, K. 3, and Heiman, J. 1,2 1 Department of Psychological and Brain Sciences, 1101 E Tenth St., Indiana University, Bloomington, Indiana 47405-7007 2 The Kinsey Institute for Research in Sex, Gender, and Reproduction, 303 Morrison Hall, Indiana University, Bloomington, Indiana 47405 3 McGill University, Department of Psychology, 1205 Docteur Penfield Avenue, Montreal, PQ, Canada H3A 1B1 METHODS Following instrument placement, participants viewed 3, 5-minute, counterbalanced films: (1) Maximally sexually arousing, (2) Moderately sexually arousing, or (3) Anxiety- inducing. Sexual arousal was reported continuously using a lever (0-100). Both instruments were analyzed as difference scores from baseline. Baseline was defined as the final 3 minutes of a 10 minute neutral film that preceded each test film. VPA responses were z-scored within participant. Raw difference scores did not change the pattern of results in the VPA, though z-scoring increased the effect sizes. CONCLUSIONS In this study, the labial thermistor was sensitive and specific to sexual arousal, and converged with subjective sexual arousal. While the sensitivity and specificity of the vaginal photoplethysmograph was replicated, its convergence with a measure of subjective sexual arousal was not replicated. The labial thermistor appears to discriminate differing levels of sexual arousal more clearly, but does not distinguish lower levels of sexual arousal and general arousal as well, as the vaginal photoplethysmograph. The two instruments did not correlate with one another. RESULTS Fifteen women between the ages of 18 and 55 (M = 22.9, SD = 9.01) with an average of 12.1 (SD = 25.3) lifetime sexual intercourse partners participated. As expected, the average level of sexual arousal reported differed significantly between conditions (F(2,28) = 8.88, p =.003 [G-G], η 2 p =.39). The sexual film was rated as more sexually arousing than the moderately sexually arousing (F(1,14) = 6.41, p =.024, η 2 p =.31) and the anxiety-inducing (F(1,14) = 13.48, p =.003, η 2 p =.49) films, and the moderately sexually arousing film was rated as more arousing than the anxiety- inducing film (F(1,14) = 5.02, p =.042, η 2 p =.26). Figure 2. Convergent validity The average correlation of each instrument with continuous reports of sexual arousal within each participant during the sexually arousing film were significantly different (t(14) = 2.22, p =.043, d pooled =.21, see Figure 2) with labial temperature (r =.42) correlating more strongly with reports of sexual arousal than vaginal pulse amplitude (r =.06). The pattern of results did not change if analyses were restricted to participants indicating sexual arousal at 10% or higher. The two instruments correlated only -.01. Sensitivity and specificity A 3 (condition) one-way ANOVA indicated that both the vaginal photoplethysmograph (F(2,28) = 5.04, p =.019 [G-G], η 2 p =.27) and the labial thermistor (F(2,28) = 5.75, p =.010 [G- G], η 2 p =.29) response differed by condition (see Figure 3). The vaginal pulse amplitude was lower in response to the anxiety-inducing film as compared to the moderately sexually arousing (F(1,14) = 10.38, p =.006, η 2 p =.43) and sexually arousing (F(1,14) = 6.14, p =.027, η 2 p =.31) films. The temperature was higher for the sexually arousing film as compared to the moderately sexually arousing (F(1,14) = 6.92, p =.019, η 2 p =.33) and anxiety- inducing (F(1,14) = 8.00, p =.013, η 2 p =.36) films. Figure 3.