This article has been cited by other articles in PMC. This study investigated whether this measure can be extended to determine age-specific sexual interest. In two experiments, the pupillary responses of heterosexual adults to images of males and females of different ages were related to self-reported sexual interest, sexual appeal to the stimuli, and a child molestation proclivity scale.
In both experiments, the pupils of male observers dilated to photographs of women but not men, children, or neutral stimuli. Female observers showed pupil dilation to photographs of men and women but not children.
In women, pupillary responses also correlated poorly with sexual appeal ratings of the stimuli. These experiments provide initial evidence that eye-tracking could be used as a measure of sex-specific interest in male observers, and as an age-specific index in male and female observers. Experimental psychology has contributed to this field by developing a number of assessment methods e.
Of these, viewing time, which reflects the duration for which particular content is studied, is now a widely utilized measure of interest in sexually appetitive materials e. In this study, we attempt to replicate those early findings with contemporary eye-tracking equipment to determine if it can be used to assess sexual interests.
This addition might be important for clinical and forensic practice. In relation to sexual interest, viewing time has been used to measure interest in preferred over non-preferred figures. Heterosexual male observers, for example, view women for longer than men Lykins et al.
These viewing patterns also appear to correspond to the sexual content on display Hall et al. Viewing patterns also appear to be age-specific. For example, male and female adult observers fixate on figures of their preferred age year olds more than babies and year olds Hall et al. However, whereas non-paedophilic adult males preferentially fixate on pictures of adults over children, paedophilic males show the reverse pattern Fromberger et al.
Despite these advantages, fixation behavior is an index of sexual interest that is vulnerable to top-down control. This limitation could be overcome by considering only the initial fixation to a stimulus display, which might reflect a covert and automatic orientation response to pre-attentively selected stimuli of sexual interest.
In line with this reasoning, heterosexual adult males tend to direct more initial fixations at women than men 56 vs. However, the difference between these percentage fixations is not indicative of a sensitive measure of involuntary behavior. In this study, we explore an alternative eye-tracking measure that might be more sensitive and not under top-down control. The pupils respond automatically to external stimulation, such as changes in lighting conditions, by increasing dilating or decreasing constricting in size.
A similar pattern is also found as an arousal response to pleasant and unpleasant stimuli Bradley et al.
This dilation has been linked to the activation of the autonomic nervous system Zuckerman, and appears to be impervious to top-down control. These characteristics might make pupillary response an ideal measure for the assessment of sexual interest.
While this is an interesting possibility, the pupillary response to sexual arousal has received little research attention. In an early study, Hess et al. Twenty measurements were obtained for each stimulus by manually measuring pupil diameter at each frame of the video footage.
Despite this elementary approach, a clear pupillary response was found whereby all heterosexual males exhibited larger pupils to pictures of women than men. By contrast, all but one of the homosexual males showed larger pupil responses to pictures of men than women.
Here, observers were presented with semi-nude and clothed images of men and women. Male observers demonstrated more pupil dilation to semi-nude women than any other stimuli. Female observers did not show different pupil responses to semi-naked and clothed stimuli or male and female targets.
However, a subsequent experiment also recorded a pupil dilation effect in female observers that appeared to be related to sexual interest Hamel, In this study, female observers showed increases in pupil size that were directly related to the degree of nudity of pictures of male, but not of female, models. Despite these promising results, there have been no attempts to replicate these findings until recently.
Rieger and Savin-Williams showed hetero-, homo-, and bisexual observers sexually explicit videos, while pupillary responses were recorded with contemporary eye-tracking equipment. This study replicated the clear relationship between sexual orientation and pupil dilation that Hess et al.
However, similar to Scott et al. In a subsequent experiment, Rieger et al. These findings indicate that pupillary response is a useful alternative for measuring sexual interest in male observers.
In addition, the lack of specificity in heterosexual female observers converges with a broad range of assessment methods e. This is an interesting finding because it suggests that pupillary responses to sexual content are also consistent with more established measures in the literature. While few studies have focussed on pupil dilation as a measure of sexual interest for photographs of adults, there has been even less research on pupillary responses to persons of different ages.
Up to now, there have been no documented attempts to replicate these findings. This is surprising considering the potential applied value of such a measurement e. For this purpose, heterosexual male and female observers were presented with images of beach scenes that contained semi-clothed adults and children, while their eye movements and pupil sizes were recorded.
These scenes contained only a single person or no persons in the case of a set of comparison landscape beach scenes. We expected the different person content of these scenes to draw attention depending on the sexual interests of the observers. For example, heterosexual male observers were anticipated to fixate on women more frequently than men see Hewig et al. Of particular interest here was whether these observers would also show an increase in pupil size to images of sexually preferred adults in comparison with sexually non-preferred adults and children.
As a secondary aim, we also sought to examine how pupillary responses to people of sexual interest are affected by image luminance. The pupils constrict in response to light i. If this differentially affects the stimulus categories in the current study, then this could influence the measurement of pupil responses as an index of sexual interest.
In turn, it is possible that the pupillary response to sexual content is clearer when luminance is controlled across different stimulus categories.
To explore this possibility, the original photographs of the beach scenes were compared with alternative versions, in which the mean luminance was equated across the different stimulus categories. This manipulation can decrease image quality by reducing light—dark contrasts.
A third version of these scenes was therefore also included, in which image quality of the original photographs was enhanced with graphics software. Experiment 1 Method Participants A total of 44 students 22 male and 22 female from the School of Psychology at the University of Kent participated in this study in return for a small payment or course credits.
Participants completed the Kinsey scale for the assessment of sexual orientation as part of a pre-screen on our online recruitment system. Only participants who reported to be completely heterosexual i. The mean age of participants was All reported normal or corrected-to-normal vision. Materials The stimuli consisted of natural beach scenes portraying men, women, and children 5 scenes for each of these four categories.
To determine the approximate age of these categories, ten observers 5 males, 5 females estimated the age of the people in the scenes in a pilot study. This revealed a mean age of The age of the children therefore corresponds to stage 1 prepubescent of the Tanner stages of sexual development see Tanner, Additionally, a set of control beach scenes without any person content 5 scenes was included, resulting in a total of 25 scenes.
People were portrayed in swim or leisure wear. All stimuli were purchased from an internet photograph database www. To confirm that these targets were of similar size, their percentage occupancy area in the scenes was calculated.