Device prompts controversy


Joseph Plaud, Ph.D., a forensic psychologist in Whitinsville, Mass., has worked with the controversial plethysmograph since the late 1980s. (photo by Tom Croke)

By Ami Albernaz

It's been called unfair, invalid, and has nearly been banned, but somehow, it has survived. In trying to predict which sex offenders will re-offend, some mental health professionals argue that it is among the most effective tools available.

The penile plethysmograph is a device intended to gauge arousal levels to visual and audio stimuli, some of it sexually explicit. It was cast briefly in the spotlight during the Kobe Bryant case, and, in Massachusetts, the Father James Porter case. Some who work with the device say that when it is used correctly, the results can be a solid component of sex offender treatment programs or valid evidence in civil commitment trials. Yet some of those same professionals will add that because of widespread problems in administering the test and interpreting results, they should be considered with caution.

The plethysmograph is a mercury-filled silicone loop that fits around the circumference of a subject's penis, and is linked by wire to a laptop computer. During a 90-minute test, images - photos of children in bathing suits, or adults engaging in a sexual act, for instance - are projected, sometimes with audio accompaniment, onto goggles that the subject wears. A weak electrical current is passed through the mercury; when the subject is aroused, the mercury thins, and the current diminishes. The strength of current is translated into digital data, and tracked on the computer.

"When employed validly, under standardized conditions, you get sound results," says Joseph Plaud, Ph.D., a forensic psychologist in Whitinsville, Mass. who has worked with the plethysmograph since the late 1980s. Plethysmography, or PPG, as researchers call it, is one of a battery of psychosexual tests Plaud administers to be used as evidence for civil commitment trials and offender treatment programs.

The plethysmograph first came into use to measure arousal in sex offenders in the 1960s. A crude version had been developed the decade before in Czechoslovakia, where it was used by the military to stop recruits from trying to get out of duty by claiming to be gay. By the early 1990s, though, the test had come under serious scrutiny because of the images of children used - photos of children taken in a nudist colony, for instance. Today, many versions of the test do not use nude photos. Plaud, for instance, has superimposed bathing suits on pictures of nude children.

Partly because there is no standard PPG test - and no standard for interpreting results or training technicians - results are not admitted as evidence in most criminal cases. Likewise, some who use PPG in their work choose only to use it as part of a treatment regimen.

"I don't want results to be misinterpreted, so I like to have the court stuff over with before using PPG," says Keith Courtney, D.O., a Concord, N.H.-based psychiatrist who uses the plethysmograph for pre-treatment and during the treatment of sex offenders. He believes that test results can be valuable in helping offenders understand their patterns of arousal and to manage them.

Potential problems with testing and interpreting results have turned one of the machine's pioneers and early advocates, Richard D. Laws, Ph.D., into an apostate. Although he still believes that the plethysmograph, when administered properly, is valuable as an assessment tool, he believes that some of problems surrounding PPG are irremediable. "People should be extremely cautious in interpreting results," he says.

In a book chapter titled Penile Plethysmography: Will We Ever Get It Right? Laws notes a 1995 survey of 48 PPG assessment centers in the United States and Canada that found that more than three-quarters of technicians had one week or less of training on the equipment, while another 18 percent had no training at all.

Currently, a group within the Oregon-based Association for the Treatment of Sexual Abusers is trying to define standards for administration of the test, Laws says.

Another problem that detractors of PPG have noted is the ease with which results can be faked. Laws says that while it is difficult to fake attraction to a stimulus that elicits no response, it is easier to suppress a reaction. Some who work with the test try to prevent cheating; Plaud, for instance, includes randomly placed flashing lights in his tests. Subjects must press a button each time he sees such a light.

In some instances, a medical condition or medication can compromise test results. Courtney says that Prozac, for instance, is known to suppress arousal. Some stages of diabetes are also associated with low arousal.

"The test is good for what it tells you, but not for what it doesn't tell you," Courtney says. "If a person shows no response, some will say, 'Oh, there must not be a problem.' But that's not the case - we can only say that there wasn't a response."

The most contentious issue concerning PPG, though, is that of its practicality. If someone is shown to have a deviant arousal - an arousal to children, for example - does that necessarily mean he will act on it?

A large meta-analysis in 1998 showed an offender's level of arousal to prepubescent children, as measured by PPG, was a strong indicator of recidivism. While the study restored the respectability of PPG, Courtney points out that the rate at which PPG results predicted recidivism - 32 percent - was fairly low.

"I have a problem with people saying because [the plethysmograph] shows deviant arousal, that a person is going to offend again," Courtney says. Even if impulses cannot be eliminated, he believes, offenders can learn to manage them through treatment.

And in spite of the problems with PPG, Laws says he doesn't expect the test to go away anytime soon. "[PPG] has survived every assault against it," he says. "It doesn't seem to matter to the true believers that it is inconsistent, unreliable, unstandardized, and that there are challenges to its validity."

And while Laws and others are optimistic that PPG might someday be governed by standards, they say it is best to proceed with caution.

"The test shows what it shows," Plaud says. "It doesn't prove or disprove allegations."

Device prompts controversy (January 2005 Issue)

Device prompts controversy
(January 2005 Issue)