Experimental research and direct-observation studies of human sexual responses often use measures of sexual arousal. In the early years of sex research, investigators had to rely largely on subjective reports of these responses. However, advances in technology over the last few decades have produced several devices for electronically measuring arousal (see I Figure 2.1).
The penile strain gauge is a flexible loop that looks something like a rubber band with a wire attached. It is actually a thin rubber tube filled with a fine strand of mercury. A tiny electrical current from the attached wire flows through the mercury continuously. The gauge is placed around the base of the penis. As an erection occurs, the rubber tube stretches, and the strand of mercury becomes thinner, changing the flow of the current. These changes are registered by a recording device. The penile strain gauge can measure even the slightest changes in penis size and is so sensitive that it can even record every pulse of blood into the penis. In the interests of privacy a subject can attach the gauge to his own penis. Researchers can also measure male sexual arousal with a penile plethys — mograph or a metal-band gauge, devices that also fit around the penis and reflect small changes in its circumference.
When a woman is sexually aroused, her vaginal walls fill with blood in a manner comparable to the engorgement of a man’s penis. The vaginal photoplethysmograph is a device designed to measure this increased vaginal blood volume. It consists of an acrylic cylinder, about the size and shape of a tampon, that is inserted into the vagina. The cylinder contains a light that is reflected off the vaginal walls and a photocell that is sensitive to the reflected light. When the vaginal walls fill with blood during sexual arousal, less light is reflected to the photocell. These changes in light intensity, continuously recorded by an electronic device, provide a measure of sexual arousal comparable to that provided by the penile strain gauge. Like the male device, the vaginal photoplethys — mograph can be inserted in privacy by the research subject. Another electronic device, the clitoral photoplethysmograph, assesses clitoral blood volume and has recently been shown to be a sensitive tool for measuring genital arousal in women (Gerritsen et al., 2009). In addition, two other devices are used to measure sexual response: The vaginal myograph and the rectal myograph are implements inserted into the vagina or rectum that measure muscular activity in the pelvic area.
a penile strain gauge
Sex Research: Methods and problems