126 undergraduate psychology students were recruited to assess the perceived age of a series of virtual characters (107 female, mean age: 22.3 yr old, SD 2.1).

The sexual stimuli are 3D virtual characters depicting realistic naked human individuals (see figure 1). Five such stimuli are used in the present study. Two adults, a female and a male, both designed to simulate individuals in their twenties, a female child and a male child, both prepubescent and aged between 10 and 12 yrs old, as well as a neutral stimulus, i.e. a textureless virtual character (see figure 1). All human-like characters were designed and developed by a team of professional 3D artists to simulate Caucasian mesomorphic body types according to Tanner's developmental criteria to fit the targeted age categories [stage 5 for the adults and stage 1 for the prepubescent children;[ Tan73 ]]. A modeling software whose rational is based on morphism was used. This software allows a progressive shaping of the characters by fusing together their global topologies as well as their local features.

Figure 1. Virtual characters used as sexual stimuli; from left to right, neutral, male adult, female adult, male child and female child (www.behavrsolution.com)

Each character was projected one after the other for a 90 second period on a giant screen installed in a classroom. They were presented in the following order: Female adult, Female child, Male Child, Male adult and Neutral. Subjects had simply to answer the following question in writing for each character: According to you, how old is the character shown on the screen?

Data are analyzed following a repeated measures multivariate analysis of variance with Sex as Between-subjects factor and Virtual characters as Within-subjects factor. Sex is used to verify how male and female subjects respectively perceived the age of the characters. Pairwise comparisons are used to compare virtual characters to each other as for their perceived age. An alpha level of .05 was used with all statistical tests.

Mean and standard deviation of perceived age for each five virtual characters are shown according to participants' sex at table 1. As a first result, we can note that the Between-subjects factor Sex is not statistically significant (Wilks = .985 ; F(4,121)=.469 ; p = .758), which seems to imply that sex does not influence the perceived age of our virtual characters. As a second result, the effect of the Within-subjects factor Virtual characters is highly significant and shows that the virtual characters are perceived as displaying distinct ages (Wilks = .113 ; F(4,121)=237.796 ; p < .001). Pairwise comparisons results presented at table 2 allow to see that adult characters are indeed perceived as adults (i.e. older than 18 year-old) and significantly older than child characters.

Then, the Female adult character is perceived as slightly younger than the Male adult. In the same way, the Female child is also perceived as younger than the Male child, the latter being seen as slightly older than planned even though he is nevertheless perceived as prepubescent in average.

Ten male SAAC participants were recruited to compose the clinical group (N=10), among which 9 had been formally recognized as guilty of sexual aggression against children and one admitting to have pedophilic interests and using juvenile pornography. These participants come from the Royal Ottawa Forensic programme, the Centre de psychiatrie légale de Montréal and the Centre d'Étude et de Recherche de l'Université de Montréal where they were involved in treatment or pre-sentence assessment. Fifteen non-deviant male subjects were recruited from newspaper ads to compose the ND group. These latter participants do not have a criminal record and assert that they do not have sexual interests toward children. Mean age of the SAAC group is 39.9 year-old (SD 13.6) while ND group's is of 45.5 year-old (SD 11.0); age difference is not statistically significant (t(23)=1.129, p=.271). Subjects of both groups were matched according to their education level and socioeconomic status. Two participants of the SAAC group are under antiandrogenic medication to reduce their libido and seven others are taking antidepressants.

We find in the SAAC group one homosexual participant sexually attracted by male children, the remaining of this group is heterosexual and attracted by female children. The ND group is composed of 4 homosexual, one bisexual and 10 heterosexual participants. Participants were met at the Laboratoire de cyberpsychologie de l'Université du Québec en Outaouais or at the Laboratoire de cyberpsychologie de l'Institut Philippe-Pinel de Montréal.

Once at the laboratory, subjects are briefed about the study and sign a consent form. They sign a consent form in which it is clearly stated that their results would not be used in any correctional or legal process and that they would remain confidential. It is furthermore made clear to them that they can withdraw from the study at anytime.

In order to assess the subjects' erectile potential (i.e. their maximum sexual response), erectile responses are recorded during the viewing of an heterosexual erotic movie for a period of 5-minute at the outset of the experimental trials. Then subjects are briefed and given a five-minute training period during which they are immersed in a realistic apartment furnished with various pieces of furniture. They are then simply asked to pay attention to the 3D animations they are about to be immersed with for five 120 second periods. Virtual characters are presented in the following order: Female adult, Female child, Male child, Male adult, and Neutral. Erectile response has to return to baseline between stimulus presentation. After the experience, subject is debriefed and given $50 to indemnify him.

A repeated measures MANOVA with Groups (ND vs SAAC) as a Between-subjects factor and Virtual characters (female adult, female child, male child, male adult and neutral) as Within-subjects factor is performed. Erectile responses expressed in ipsative z-scores are used as the dependent variable. Independent T-tests are computed in the context of significant multivariate effects. An alpha level of .05 is used for all statistical tests.

Figure 2 shows erectile response profiles according to Groups and Virtual characters factors. Using Wilks' Lambda criterion, the repeated measures MANOVA gives a non significant main effect for the Within-subjects factor (Wilks = .661 ; F(4,20) = 2.561 ; p = .070), even though it is rather close to be so. However, the interaction effect between the latter and the Between-subjects factor Groups is on the other hand statistically significant (Wilks = .489 ; F(4,20) = 5.235 ; p < 0.01). Simple effects for this interaction effect are verified from independent T-tests shown at the table 3. SAAC and ND groups differ significantly as for erectile response when facing Female child and Male adult, with SAAC participants being more sexually aroused by the first stimulus while the reverse is observed for the second one. Female adult and Male child, as well as Neutral stimuli do not statistically distinguish groups between them, even though the expected tendencies are noticed (see figure 2). The fact there are 5 homosexual or bisexual participants out of ten in the ND group, while there is only one in the SAAC group, may help to explain why the Male adult character is more distinguishing than the Female adult one. Increasing sufficiently the number of subjects in each sexual orientation category would possibly allow clearer comparisons on that matter. Also, the reason why Male child character is not distinguishing between groups is most probably attributable to the fact that there is only one participant attracted to prepubescent male child in the SAAC group. When compared to those of the ND group (AVG = -0.419, SD = .456, test value = 1.27; t(14) = 14.349, p =< .001) or even with those of his own group (AVG = -0.261,SD .509, test value = 1.27; t(8) = 9.017, p < .001), the score of this homosexual pedophile subject is highly statistically different, with a higher sexual arousal engendered by the Male child virtual character.

Both groups thus present distinct multivariate profiles according to the virtual characters they were immersed with. Non deviant subjects (ND) show higher sexual arousal when facing virtual characters simulating adult primary and secondary sexual character. On the other hand, subjects known for their sexual attraction to prepubescent victims (SAAC) respond more strongly to virtual stimuli mimicking sexual features belonging to children aged between 10 and 12 year-old.

Figure 2.  Erectile response profiles according to Groups and Virtual characters

However, to more closely fit singular sexual preferences, the inherent malleability of virtual characters can be used in designing made-to-measure virtual sexual stimuli. This method could be either an alternative or a complement to a standardized set of virtual characters validated with a sample of patients coming from specific forensic clinical populations.

Two patients were met at a maximum security psychiatric hospital (Institut Philippe-Pinel de Montréal) by a clinical psychologist specialized in forensic assessment and treatment of sex offenders. This psychologist conducted interviews with and case file reviews of the aforementioned patients in order to draw-up individualized sexual preference profiles. These profiles were then used to inform the design of virtual characters to match the individualized preferences sketched out by the clinical psychologist. The following clinical vignettes give details about these patients and present virtual characters prepared by the clinical psychologist from a high-definition avatar generator software.

Michael, 31 years old, is serving a 2 year sentence for Forcible confinement, Use of weapon and Attempt to commit a criminal act. He is assessed as being a low functioning individual.

The victim of the index offences is a 14 year-old female, unknown to the offender. She was walking home after school. Michael grabbed her by the arm and said "You are coming with me". She resisted and hit him with her school bag, putting an end to Michael's attempt to isolate the victim and sexually assault her. He was arrested a couple of minutes later and police officers found a knife in his pocket. Prior to this incident, Michael reports that he spent hours watching female adolescents in parks or school yards. For many years, he would fantasize about having sex with these young females. Over the years, his fantasies became more intrusive and violent. Michael reports that when he approached the victim, he had planned to kidnap her and force her to intercourse. He planned to use his knife if the victim was to resist. However, he backed off when he encountered real resistance from the victim. In addition, Michael reports being aroused by cross-dressing and SM role plays (where he would insult and/or physically hurt his partner).

When asked to described his sexual preference, Michael talks about teenage girl (13 to 17 years old), with small breasts (A cup. During phallometric testing, he repeatedly responded with greater erection to audio stimuli depicting sex with pre-pubescent girl then to audio stimuli depicting consensual sex between adults. He reports being attracted to domination/humiliation of his partner.

Figure 3.  Virtual characters depicting a female adolescent designed according to the sexual preferences expressed by the patient whose case is described in clinical vignette one (www.behavrsolution.com).

Domingo, is a 33 year-old latino-canadian serving a nine year sentence for Sexual Assault (one count) and Armed Sexual Assault (four counts). All his victims were female, aged 16 to 25 and unknown to the offender. During a period of two months, Domingo cruised around the city in his car, looking for potential victims. He selected the women based on availability and looks (nice firm behind, big breasts and sexy clothing). Domingo followed the victims until they reached a secluded area. He then pushed the victims against a building and forced them to diverse sexual acts (including fondling, kissing, fellatio, and penetration). Although he was charged for Armed Sexual Assault, no weapon was ever used during the offences. However, on four occasions, Domingo pretended to be armed with a knife. Domingo used death threats and physical violence (strangling, punching) during the offenses.

At plethysmographic testing, Domingo presented a deviant profile responding higher to sexual assault with violence scenarios than to consensual heterosexual scenarios.

Figure 4. Virtual characters depicting a female adult designed according to the sexual preferences expressed by the patient whose case is described in clinical vignette two (www.behavrsolution.com).