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Penile plethysmography

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The penile plethysmograph (PPG) is a controversial type of plethysmograph that measures changes in blood flow in the penis in response to audio and/or visual stimuli. It is typically used to determine the level of sexual arousal as the subject is exposed to sexually suggestive content, such as photos, movies or audio. It has been demonstrated by most studies to be the most accurate method of identifying which sexual offenders will go on to commit other sexual crimes against children, although some clinicians disagree with using it at all.

Significant suppliers of PPG machines include Behavioral Technology Inc. and Medical Monitoring Systems. The device is known to be used in Brazil, Britain, Canada, China, Czech Republic, Hong Kong, New Zealand, Norway, Slovak Republic, Spain, and the United States.

Types

There are two types of penile plethysmograph:

  • Volumetric air chamber: When this is placed over the subject's penis, as tumescence increases, the air displaced is measured.
  • Circumferential transducer: This uses a mercury-in-rubber or indium/gallium-in-rubber ring strain gauge and is placed around the shaft of the subject's penis to measure changes in circumference.

The circumferential type is more common, but the volumetric method is more accurate.

Development and uses

The original air device was developed by researcher Kurt Freund in Czechoslovakia during the 1950s. He later wrote, "In the early fifies homosexual interaction was still an indictable offense in Czechoslovakia. I was of course opposed to this measure, but I still thought, as did my colleagues at the psychiatric university hospital in Prague where I was working, that homosexualiy was an experientially acquired neurosis" (p. 223) He then developed phallometry to replace psychoanalytic methods of assessment because "sychoanalysis had turned out to be a failure, virtually unusable as an instrument for individual diagnosis or research....When phallometry began to look promising as a test of erotic sex and age preferences, we started using it mainly as a test of pedophilia, that is determining who has an erotic preference for children over adults" (p. 223-224).

Each different application of phallometry requires its own validation. Phallometry has been shown successfully to distinguish gay men from straight men. It has been shown to distinguish pedophilic men from nonpedophilic men. Phallometry can distinguish men with erotic interests in cross-dressing from non-cross-dressers. There is some evidence that phallometry can distinguish groups of men with a paraphilia involving rape from groups of men without it.

United States

According to Barker and Howell, penile plethysmography (PPG) cannot meet most legal thresholds as a valid or relevant diagnostic tool for the following reasons:

  • No standardization
  • Test results are not sufficiently accurate
  • Results are subject to faking and voluntary control by test subjects
  • High incidence of false negatives and false positives
  • Results are open to interpretation

In State of North Carolina v. Spencer, the court reviewed the literature and case law and concluded that penile plethysmography was scientifically unreliable: "Despite the sophistication of the current equipment technology, a question remains whether the information emitted is a valid and reliable means of assessing sexual preference."

The penile plethysmograph is not intended to be used as a guilt or innocence tool, but rather as a supplemental device to add to a complete psychosexual evaluation. Some of the criticisms of PPG articulated by various criminal courts relate to the blatant misuse of PPG as a tool to determine whether a defendant committed a particular crime.

In recent years, a substantial amount of research data has been gathered and reviewed, and significant steps have been taken toward standardization.

The device has also been used in many states when evaluating convicted sex offenders. The sexual assault trial of basketball player Kobe Bryant in Colorado brought this device and its use to public attention before the case was dropped in 2004, because Colorado law would have required evaluation with this device following conviction.

During the priest sexual abuse scandal, the reliability of the test was questioned by some diocesan officials in Philadelphia, PA. Later, these officials chose to seek therapy at an institution where the plethysmograph was not used. This, even though the officials were made aware of the fact that the test was used by most experts and was believed to be of value in diagnosing sexual disorders. Later, a Grand Jury found that the Archdiocese of Philadelphia's decision to do so "had the effect of diminishing the validity of the evaluations and the liklihood that a priest would be diagnosed as a pedophile or ephebophile."

The Ninth Circuit Court of Appeals recently addressed the procedures required before a supervised release program could include penile plethysmograph testing.

Canada

Courts in Canada came to a similar conclusion as the United States. While the Daubert decision was greeted with harsh criticism from those who feared a flood of "junk science" in courtrooms, the Supreme Court of Canada adopted the Daubert doctrine in R. v. J. (J.L.) 2 S.C.R. 600 with very little fanfare. Interestingly, this statement by the court was contained in a decision which upheld a lower court's decision to exclude testimony by a psychiatrist who had administered several tests on the accused, including a penile plethysmograph.

After developing the device in Czechoslovakia, developer Kurt Freund fled to Canada in the wake of the Prague Spring. Freund then began using the device at the Clarke Institute in Toronto, where much of the research and published data using the device originated.

A roughly equivalent procedure for women, vaginal photoplethysmography, measures blood through the walls of the vagina, which researchers claim increases during sexual arousal.

See also

References

  1. Hanson, R. K., & Bussière, M. T. (1998). Predicting relapse: A meta-analysis of sexual offender recidivism studies. Journal of Consulting and Clinical Psychology, 66, 348–362.
  2. Howes, R. J. (1995). A survey of plethysmographic assessment in North America. Sexual Abuse: A Journal of Research and Treatment, 7, 9-24.
  3. Kuban, M., Barbaree, H. E., & Blanchard, R. (1999). A comparison of volume and circumference phallometry: Response magnitude and method agreement. Archives of Sexual Behavior, 28, 345–359.
  4. Freund, K. (1991). Reflections on the development of the phallometric method of assessing sexual preference. Annals of Sex Research, 4, 221–228.
  5. Adams, H. E., Mostinger, P., McAnulty, R. D., & Moore, A. L. (1992). Voluntary control of penile tumescence among homosexual and heterosexual subjects. Archives of Sexual Behavior, 21, 17–31.
  6. Freund, K. (1963). A laboratory method of diagnosing predominance of homo- and hetero-erotic interest in the male. Behaviour Research and Therapy, 1, 85–93.
  7. Freund, K. (1967). Diagnosing homo- or heterosexuality and erotic age preference by means of a psychophysiological test. Behavioral Research and Therapy, 5, 209–228.
  8. Blanchard, R., Klassen, P., Dickey, R., Kuban, M. E., & Blak, T. (2001). Sensitivity and specificity of the phallometric test for pedophilia in nonadmitting sex offenders. Psychological Assessment, 13, 118–126.
  9. Freund, K., & Blanchard, R. (1989). Phallometric diagnosis of pedophilia. Journal of Consulting and Clinical Psychology, 57, 100–105.
  10. Murphy, W. & Barbaree, H. E. (1994). Assessments of sexual offender by measures of erectile response: Psychometric properties and decision making. Brandon, VT: Safer Society Press.
  11. Buhrich, N., & McConaghy, N. (1977). The discrete syndromes of transvestism and transsexualism. Archives of Sexual Behavior, 6, 483–495.
  12. Freund, K., Seto, M. C., & Kuban, M. (1996). Two types of fetishism. Behaviour Research and Therapy, 34, 687–694.
  13. Seto, M. C., & Kuban, M. (1996). Criterion-related validity of a phallometric test for paraphilic rape and sadism. Behaviour Research and Therapy, 34, 175–183.
  14. Barker and Howell, The Plethysmograph: A Review of Recent Literature, 20 Bull. Am. Acad. of Psychiatry and Law 13 (1992)
  15. North Carolina v. Spencer, 459 S.E.2d 812, 815 (N.C. Ct. App. 1995),
  16. Court of Common Pleas, First Judicial District of PA, County Investigating Grand Jury, 9-17-2003
  17. United States v. Weber, 2006 U.S. App. LEXIS 15111 (9th Cir. 2006).

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