The penile plethysmograph (PPG) is a machine that measures changes in the circumference of the penis.
A band is fitted around the subject's penis, and the device senses changes in penis size, usually when connected to a computer. It is typically used to determine the level of sexual arousal as the subject watches sexually suggestive or explicit content, such as pornographic photos, movies or audio. It has been used in law enforcement and originally, in Czechoslovakia to determine whether subjects who were claiming they were gay in order to avoid military service.
The device has also been used in psychological experiments. One study demonstrated that experimental subjects could be conditioned to show sexual arousal (as indicated by the device) in response to images of shoes, by initially preceding the shoe images with pictures of nude women. The experimenters inferred that the behaviourist concept of conditioning was likely to be an important influence in sexual fetishes. Use in a research setting has attracted little attention or controversy.
Significant suppliers of PPG machines include Farrall Instruments Inc., Medical Monitoring Systems and Behavioral Technology Inc. The device is known to be used in China, Hong Kong, Norway, Britain, Brazil and Spain.
A roughly equivalent device for women, the vaginal plethysmograph, measures blood through through the walls of the vagina, which increases during sexual arousal.
United States
The device has also been used in many states when evaluating convicted sex offenders. The trial of well known basketball star Kobe Bryant in Colorado has brought this device and its use to more public attention. If Bryant is found guilty of committing a rape, Colorado's tough laws will require his undergoing evaluation with this device.
