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[Capter 4 - First Section]


[Page 103]

"It is worth remembering that from ancient times Christian theologians, also, regarded the penis as evil and a shameful reminder of our animal natures. The fact that we call them private parts, which must never be exposed in public, adds to our fear and anxiety. The fear persists because, just as men in the Western world believe that the head is the seat of the soul, they are equally deluded in thinking that sexuality exists in the penis. This may explain our longstanding anxiety about its size and the current zeal to find causes of sexual aggression in the frequently measured but highly overrated appendage."
(Greenland, 1988, pp. 377-378)

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
research has described devices measuring changes in penis size and how to interpret these.

These techniques, collectively known as either phallometry or plethysmography, are basically of two main types. 

The first, and earlier, type involves penis volume: a plastic ring is slipped along the penis and an inflatable cuff, made from a condom, is attached (Freund, 1963). 
The other end of the cuff connects with a glass cylinder which fits over the penis. The condom is inflated and changes in the size of the penis are transmitted through variations in air pressure within the condom to a meter (or electrical pen recorder, which makes a graph of the changes during assessment). 

[Page 104]

The alternative procedure deals with changes in penis circumference (Fisher, Gross and Zuck, 1965). 
The penis stretches a flexible "tube" placed around the shaft of the penis, and this movement is converted into electrical signals. (Any device that turns physical changes into electrical information is called a transducer.) The original "strap" contained the liquid metal mercury, which was pushed up a glass tube by expansion of the penis, rather like a barometer that reacts to changes in penis pressure rather than atmospheric pressure. Increasingly, electrical pen recorders were substituted for their added flexibility and ease in recording change.

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. 

(At the time, study of the dilation and constriction of the eye was popular as an indirect measure of attraction and repulsion to various stimuli - e.g. Hess, 1965). 

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. 

[Page 105]

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: 

"I really like little kids. They like me too. They always seem to want to climb on my knee or play horsie with me. I feel so good when I see them come running to me when I go into the room. They want to climb on my lap and wriggle around and cuddle up to me. They're so soft and cute. 
I hope she wants to sit on my lap today. She's the cutest one. It feels so good when I'm there. I just want to touch her a bit. Maybe we can do it in the other room. It feels good when she squirms around. Maybe she'll want to touch it. I could get her to do some things if we played some games. She seems to know all about it so it can't hurt her." 
(Farrall and Card, 1988, p. 268) 

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 

(Baxter, Barbaree and Marshall, 1986; Baxter et at. , 1984; Murphy et al. , 1986) 

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. 

[Page 106]

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: 

"Thus, it is extremely difficult to obtain a set of visual stimulus materials that is both stimulating and legally obtained" (p. 264).

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

[Page 107]

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: 

"1. When lying in bed and sexually aroused, do you imagine or fantasize about intimately touching 

a) boys or girls up to 10 years old, 

b) boys or girls 12-15 years old, 

c) boys or girls in both age ranges, 

d) none of the above? 

2. When lying in bed and sexually aroused, do you imagine or fantasize about intimately touching females 17 and over more often than touching children or teenagers 15 years or younger? 

a) yes 

b) no." 

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. 

Fifty-five per cent of non-admitters were correctly categorized as attracted to children whereas 

95% of the non-paedophile controls were correctly diagnosed as being sexually attracted to adult women. 

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. 
Furthermore, this was after eliminating a number of individuals from the research because of their low levels of erection to the stimuli and because there were signs of deliberate attempts to influence the phallometric test outcome. 
Additionally, since the phallometric test cannot differentiate between those who prefer adult women and those attracted to adolescent girls, men who had 

[Page 108]

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:

"The results of clinical diagnostic phallometric tests should be exclusively available to and interpreted by behavioral sexologists with medical or psychological degrees ... We do not condone the use of diagnostic phallometric tests by narrowly informed technical experts or their application in the same manner in which lie detector procedures are sometimes administered."
(Freund and Blanchard, 1989, pp. 104-105)

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.

[Page 109]

Table 4.1. 
Amounts of erection (average proportions of maximum recorded erections) by offenders to different types of slide 


Female incest

Female adolescent paedophile

Female paedophile

Adult female




Adolescent female




Young female




Adult male




Adolescent male




[Page 108 continued]

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

[Page 109 continued]

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 females! 
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. 

[Page 110]

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.

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