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[Capter 4 - First Section]
The idea that it is possible to gain insight into sexuality, even deviant
sexuality, by investigating the penis is well established in work with sex
offenders. Since the 1960s, a steady stream of
These techniques, collectively known as either phallometry or plethysmography, are basically of two main types.
A different approach is taken when changes in the sexual arousal of women are measured.
Vaginal plethysmography is usually based on changes in vaginal blood volume. The amplitude and rate of blood pulse in the vagina can also be measured (Cooper et al., 1990). Sometimes changes in the temperature of the vagina are measured instead. The use of such devices on women is exceptional and is rarely discussed in professional publications.
There have been attempts to measure men's sexual interest in children under laboratory conditions using other measures.
For example, Attwood and Howell (1971) measured the size of the pupil of the eye in response to pictures.
Slides of nude women produced dilation in nearly all controls but constriction in a group of child abusers. More-or-less the reverse pattern was produced in the response to pictures of underage girls. However, the data were rather more unclear than this suggests. For example, the greatest constriction to the nude women was found for one normal man. No further research on this vein seems to have been carried out. Pupillometry, as it was called, was probably too fraught with technical problems.
All of these procedures are limited to laboratory applications because of the bulkiness of the apparatus. No one has yet even attempted to produce a plethysmographic apparatus so unobtrusive that the day-to-day arousal of the paedophile can be continuously monitored. There is no alarm system that could warn of the genital arousal of a child molester -- electronic tagging of the penis. In the usual context of a hospital assessment, a man is shown or hears material portraying one of several different sorts of sexual and non-sexual content. The age and sex of the people portrayed is varied, as well as aspects such as violence or coercion.
Some studies use slides; some video, some tape-recorded descriptions and some mixtures of slide and tape. The material can be tailored to the sexual proclivities of the individual being assessed, and often the men generate their own fantasies for the research. This flexibility has enormous advantages since what is sexually arousing for one man may have no effect on another.
The following is typical of the fantasy that can be used to accompany slides of pre-pubescent girls:
Some researchers and clinicians encourage the men to fantasize actively about the material, especially when slides alone are being used without any commentary.
It is a mistake to believe that phallometric methods constitute a simple and precise measure of sexual arousal (much as a barometer of passion). Volume and circumference measures can vary considerably.
For example, in one study, the two types of measuring device were attached at the same time in order to compare their relative readings in identical circumstances (Freund, 1981). While the two measures correlate to a degree, penis volume was more effective than circumference at distinguishing between different types of erotic material. The two types of measure can even show opposite trends in research outcomes.
Penis circumference has not been shown to differentiate rapists from normals
although penis volume has (McConaghy, 1991). Similarly, although Quinsey et at. (1975) claimed that molesters of female children were likely to have their maximum penis circumference in response to pictures of nude female children, two other studies failed to demonstrate this (McConaghy, 1991).
There is no standard penis size against which to measure the amount of erection achieved. Penises fluctuate in flaccid size and shape at different times, so the question, "how big is a penis at full erection?" becomes important.
The relative crudity of the measuring devices, partly caused by the variability of placing the apparatus on the shaft of the penis, means that absolute measures of arousal are impossible. Normally, measures are taken when the penis is limp and then when it is as erect as it gets in the laboratory; the man masturbates to full erection (alternatively, his greatest erection to any stimulus is used). In this way it is possible to express the amount of erection to a particular erotic slide as a percentage of the maximum size previously obtained.
In other contexts, Abel et al. (1977) developed a rape index and Avery-Clark and Laws (1984) a dangerous child molester index. Both of these are dependent entirely on the relevant amount of arousal the man has to sexually violent slides compared with more neutral ones.
Some offenders fail to have any erection to the erotic material; about one in ten men is largely unresponsive (Travin et al., 1985b). Many clinicians disregard data from such unresponsive men. Since the apparatus is relatively imprecise, there is a certain amount of variability in the readings which may swamp the effects of the erotic stimuli. Conventionally, cases are disregarded as uninterpretable when the apparent response to the erotic material is less than 10% of the man's maximum erection.
Some researchers apply similar criteria, thus selecting participants who show the largest erections and eliminating those who do not respond much. This can sometimes equate to loading the dice.
There are other problems.
One is the non-linearity of penis size. That is to say, the apparatus does not consistently show a uniform increase in reading for a given increase in circumference or volume of the penis. This, in general, would only be a difficulty for those inclined to regard the data obtained in such assessments as more finely honed than they actually are.
Furthermore, Farrall and Card (1988) point out that in the USA federal and state anti- pornography laws prohibit the possession of or taking of nude pictures of children:
For illustrative purposes, we can take a study of phallometry's ability to differentiate between sexual offenders (Freund and Blanchard, 1989).
Male outpatients (age range 18-55 years) attending the Clarke Institute of Psychiatry's Sexology Clinic in Canada were used. Some had offended against children, others against mature males. About one in eight offenders were excluded
because they had offended against both age groups. Two items (from an unpublished questionnaire) were used to assess whether the offender denied that his strongest erotic feelings were for underage children:
These questions were designed to distinguish between known offenders who admitted abusive thoughts and those who denied such feelings.
In the phallometric assessment, videos of nude people walking slowly towards the camera were shown. The images included physically mature women, early adolescent girls, 8-11-year-old girls, and 5-8-year-old girls as well as males in these four age categories. Landscapes with no erotic significance served as non-erotic control stimuli.
Using data on the relative amounts of erection to adults arid children, and males and females, it was possible to form indices of both age and sex preference. A computer program chose cut-off points on these indices, which optimized the number of offenders against children classified as paedophiles or hebephiles, while at the same time minimizing the number of offenders against adults misclassified as offenders against children. This was done for part of the sample; the criteria developed on this basis were then tested on the rest.
This is, of course, somewhat disappointing. The panoply of physiological apparatus and computers did relatively badly at picking out the paedophiles from among those convicted of such offences but who did not admit to paedophiliac thoughts and fantasies.
only approached 11- to 16-year-old girls had already been excluded from the study.
Of course, such findings place limitations on the use of phallometry in assessing the likelihood of paedophilia in individuals who deny their offending. Very little is known about the tests when applied to non-forensic cases (Freund and Blanchard, 1989). Even if the pattern on the assessment indicates paedophilia, this is not proof that the man has committed any particular offence that he may be charged with. Freund and Blanchard (1989) conclude that the complexity of interpretation of this phallometric data make it inappropriate for simplistic interpretation by casually trained staff:
Travin et al. (1985b) present a rather overly positive account of the use of laboratory assessment.
Table 4.1 gives their data on the physical arousal of three sexual offenders prior to treatment. One was an incest offender against his daughter, the second was a paedophile who offended against the adolescent female age group and the third was a paedophile who offended against girls. The percentages are the average proportions of each man's maximum recorded erection produced by each of five different types of slides. The bigger the percentage, the greater his response. In general, all three offenders were aroused by adolescent females and all but the incest offender by young female children. The incest offender seems aroused by adult females, as was the paedophile who offended against female children. None responded to adult males. The incest offender showed moderate arousal to pictures of adolescent males.
Female adolescent paedophile
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Travin et al. recommend phallometric data as a means of confronting the offender with the actuality of his offending. So, for example, the female incest offender initially acknowledged only fondling his daughter but on confrontation with this data (which show high arousal to adolescent females) he admitted repeated oral sex with his 12-year-old daughter and having sex with an adolescent female outside of the family. The offender against adolescent females initially acknowledged sexually abusing an adolescent female but
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denied other paraphilias until his phallometric data became available, when he admitted abusing several young females and one adolescent male:
"Many offenders flatly deny having a paraphiliac disorder or minimize the extent of the problem ... Confronting the offender with the laboratory results frequently elicits admissions of sexual deviation(s) or more detailed and accurate reports on the frequency and nature of the paraphilia. Resistance is an issue in any therapy, but with sex offenders therapy is unlikely to be beneficial until the offender is willing at least to admit to sexual deviation. Laboratory assessment via the penile transducer is effective in confronting this type of resistance."
(Travin et at., 1985b, p. 617)
There may be an element of wishful thinking in this (McConaghy, 1991). The particular
measurement technique used lacks comparative data from normal, non-offending men.
A study by Quinsey et al. 1975) found that normal men's erections to pictures of
pubescent and younger girls averaged 70% an 50% of their responses to adult
Furthermore, Travin et al.'s offender who admitted offending against an underage male following "confrontation" did not have his highest response to pictures of adolescent males.
Given this, it may not be too tongue-in-cheek to suggest that if "confession" is the object, offenders could be shown fictitious laboratory results in the hope that these might elicit disclosure. The more serious point to this is that such tests are used in some parts of the world in the assessment of sex offence cases to serve law enforcement agencies. The problem associated with phallometry lead Schouten and Simon (1992) to caution clicians about their integrity and the rights of the accused.
Nevertheless, Farrall (1992) presents a detailed and thorough discussion of how to use phallometry. This is positive about the technique and rather underplays the broader implications of the limitations that others highlight.