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Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli

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Pupil dilation to explicit sexual stimuli (footage of naked and aroused men or women) can elicit sex and sexual orientation differences in sexual response. If similar patterns were replicated with non-explicit sexual stimuli (footage of dressed men and women), then pupil dilation could be indicative of automatic sexual response in fully noninvasive designs. We examined this in 325 men and women with varied sexual orientations to determine whether dilation patterns to non-explicit sexual stimuli resembled those to explicit sexual stimuli depicting the same sex or other sex. Sexual orientation differences in pupil dilation to non-explicit sexual stimuli mirrored those to explicit sexual stimuli. However, the relationship of dilation to non-explicit sexual stimuli with dilation to corresponding explicit sexual stimuli was modest, and effect magnitudes were smaller with non-explicit sexual stimuli than explicit sexual stimuli. The prediction that sexual orientation differences in pupil dilation are larger in men than in women was confirmed with explicit sexual stimuli but not with non-explicit sexual stimuli.
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Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
Tuesday M. Watts and Luke Holmes
University of Essex
Ritch C. Savin-Williams
Cornell University
Gerulf Rieger
University of Essex
Author Note
Tuesday Watts and Luke Holmes, Department of Psychology, University of Essex;
Ritch C. Savin-Williams, Department of Human Development, Cornell University;
Gerulf Rieger, Department of Psychology, University of Essex.
This research was supported by the American Institute of Bisexuality, the United
States Department of Agriculture (NYC-321421), and the University of Essex.
Correspondence concerning this article should be addressed to Gerulf Rieger,
Department of Psychology, University of Essex, Colchester C04 3SQ, UK. Email:
gerulf@essex.ac.uk
Word Count: Abstract (149); Main Text (6445)
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Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
Abstract
Pupil dilation to explicit sexual stimuli (footage of naked and aroused men or women)
can elicit sex and sexual orientation differences in sexual response. If similar patterns
were replicated with non-explicit sexual stimuli (footage of dressed men and women),
then pupil dilation could be indicative of automatic sexual response in fully non-invasive
designs. We examined in 325 men and women with varied sexual orientations, whether
dilation patterns to non-explicit sexual stimuli resembled those to explicit sexual stimuli
depicting the same sex or other sex. Sexual orientation differences in pupil dilation to
non-explicit sexual stimuli mirrored those to explicit sexual stimuli. However, the
relationship of dilation to non-explicit sexual stimuli with dilation to corresponding
explicit sexual stimuli was modest, and effect magnitudes were smaller with non-explicit
sexual stimuli than explicit sexual stimuli. The prediction that sexual orientation
differences in pupil dilation are larger in men than in women was confirmed with explicit
sexual stimuli but not with non-explicit sexual stimuli.
Keywords: pupil dilation, sexual arousal, sexual orientation, sex differences
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Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
Sexual orientation is a critical motivational drive that influences humans in
forming romantic and sexual relationships, mating, and reproduction (Rahman & Wilson,
2003). Despite this relevance, various recommendations exist regarding how to assess
sexual orientation in a reliable and valid manner (Chivers, Seto, Lalumière, Laan, &
Grimbos, 2010; Korchmaros, Powell, & Stevens, 2013; Sell, 1997). Although self-report
measures are the most common, because of the stigma associated with nonheterosexual
orientations, self-reports can, in some cases, be ambiguous or distorted if participants are
not able or willing to fully disclose their sexual orientation (Friedman et al., 2004; Herek,
2004; Ragins, Singh, & Cornwell, 2007). Some research has therefore focused on an
automatic correlate of sexual orientation, genital arousal, which is not affected by the
cognitive limitations of self-report (Janssen, Prause, & Geer, 2007; Seto, Lalumière, &
Blanchard, 2000). It has been argued that in certain cases where self-report does not
match genital response, that the latter might, in fact, be the more accurate indicator of
sexual orientation (Bailey, 2009). With measures such as penile strain gauges and vaginal
plethysmographs, effects of sexual orientation on genital response, and sex differences in
these effects of sexual orientation, have been repeatedly described (Bailey, 2009;
Huberman & Chivers, 2015; Rieger et al., 2015a; Suschinsky & Lalumière, 2011).
Yet, a considerable disadvantage of genital arousal measurement is its
invasiveness (Strassberg & Lowe, 1995), which makes many people opt out of such
experiments (Chivers, Rieger, Latty, & Bailey, 2004; Wolchik, Spencer, & Lisi, 1983),
and those who volunteer may not represent the general population. We have therefore
studied an alternative measure of automatic sexual arousal: pupil dilation to sexual
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Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
stimuli (Rieger et al., 2015a). Participants are arguably more likely to take part in
experiments that assesses their eye gaze rather than their genital response.
Pupil dilation to stimuli reflects activation of the autonomic nervous system (Lang
& Bradley, 2010), which affects other automatic and semi-automatic processes such as
genital response, perspiration, digestion, blood pressure, heart rate, and breathing (ten
Donkelaar, Němcová, Lammens, Overeem, & Keyser, 2011). Pupils responding to stimuli
likely indicate attention that is not in the conscious control of participants (Heaver &
Hutton, 2011). For these reasons, pupil dilation has been used as a measure of automatic
responses, for example, in studies on implicit reaction and cognitive load, as well as for
studies on sexual interest (Goldinger & Papesh, 2012; Laeng, Sirois, & Gredebäck,
2012). Pupils tend to dilate more to sexual stimuli depicting an individual’s preferred sex
than to stimuli of the other sex or to non-sexual stimuli (Hess & Polt, 1960; Hess, Seltzer,
& Shlien, 1965; Rieger & Savin-Williams, 2012). In fact, dilation to sexually preferred
stimuli appears to be the strongest pupillary response elicited by stimuli (Laeng et al.,
2012). These findings point to the utility of this measure for research on sexual attraction
and arousal.
In general, pupil dilation patterns to sexual stimuli mirror genital arousal to such
stimuli: with either measure, the link of sexual orientation with sexual responses to the
same sex or other sex is stronger in men than in women (Bailey, 2009; Chivers, Seto, &
Blanchard, 2007; Rieger et al., 2015a; Rieger & Savin-Williams, 2012). This difference is
most obvious when sexual orientation is related to a contrast score of sexual response
(i.e., responses to the same sex minus responses to the other sex). In men, such
relationships tend to be strong in effect. Heterosexual men respond most to the other sex,
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Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
homosexual men respond most to the same sex, and bisexual men show, on a group level,
responses that are in-between those of heterosexual and homosexual men (Bailey, Rieger,
& Rosenthal, 2011; Rieger et al., 2013; Savin-Williams, Rieger, & Rosenthal, 2013). In
women, both pupil dilation and genital arousal patterns are weakly related to their sexual
orientation, largely because heterosexual and bisexual women respond similarly to both
sexes, whereas lesbians are somewhat more aroused to their preferred sex (women) than
the other sex (Chivers et al., 2007; Rieger, Savin-Williams, Chivers, & Bailey, 2015b).
In addition to similar sex differences in the relationship of sexual orientation with
sexual response, pupil dilation and genital arousal patterns show a similarity in a further
sex difference. The correspondence of these measures with each other and with other
responses to sexual stimuli, including subjective arousal, or time spent viewing these
stimuli, is stronger in men than in women (Chivers et al., 2004; Chivers et al., 2010;
Rieger et al., 2015a; Rieger & Savin-Williams, 2012). It is possible that for men, more
than for women, stronger congruencies between various indices of their sexual arousal
aid them in staying sexually oriented towards relevant targets (Rieger et al., 2015a). But
regardless of the ultimate reasons for these differences, distinctions between the sexes
and between sexual orientation groups, as reported with genital arousal measures, can be
replicated with the assessment of pupillary response.
In the research reviewed thus far, highly explicit sexual stimuli have been
employed (for example, two people engaged in sexual intercourse or one person
masturbating). For the assessment of genital arousal, highly explicit sexual stimuli elicit
the strongest responses (McConaghy, 1999), and for similar reason, explicit sexual
stimuli have also been used for assessing pupil dilation (Hess & Polt, 1960; Rieger et al.,
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Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
2015a; Savin-Williams et al., 2013). However, viewing such stimuli can be invasive in
itself and may limit researchers in recruiting a diverse range of participants. Moreover, in
many countries the viewing of explicit sexual stimuli is illegal, restricting research with
such measures to Westernized societies that may not be representative of the global
population (Henrich, Heine, & Norenzayan, 2010). Because non-explicit sexual stimuli,
such as footage of attractive but dressed men and women, are for some participants likely
to be less invasive than explicit sexual stimuli, using such non-explicit sexual stimuli can
be helpful for research on populations where it is inadvisable or unethical because of the
participant’s age, personal values, or cultural context to show explicit sexual stimuli.
As pupils are highly sensitive to attention-triggering stimuli, and this even within
a few seconds of exposure to stimuli (Bradley, Miccoli, Escrig, & Lang, 2008; Laeng et
al., 2012), they might, in fact, not need the same degree of explicit sexual stimulation as
genitals do to show reliable reactions that correspond with a person’s sexual orientation
or sex. Thus, if pupil dilation to non-explicit sexual stimuli relates to dilation to explicit
sexual stimuli, then dilation patterns with the first measure could reflect dilation patterns
with the second measure (and, by extension, reflect previously described genital
responses to explicit sexual stimuli). Support for the possibility that non-explicit sexual
stimuli elicit responses similar to explicit sexual stimuli comes from another measure of
gaze, viewing time. Time spent viewing stimuli depicting swimsuit models yielded
attraction patterns that mirror patterns of genital arousal: on average, men viewed their
preferred sex more strongly than women did, but within women, homosexual women
tended to view their preferred sex more strongly than heterosexual women did (Lippa,
2012). Similar sex and sexual orientation differences were described in another study
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Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
with a viewing time paradigm (Ebsworth & Lalumière, 2012). Moreover, a recent study
suggests that heterosexual men dilated to female models but not to male models in swim
suits, whereas heterosexual women dilated to both sexes (Attard-Johnson, Bindemann, &
Ó Ciardha, 2016). In combination, these studies raise the possibility that predicable sex
and sexual orientation differences are elicited with pupil dilation to non-explicit sexual
stimuli.
It is further possible that any responses elicited with non-explicit sexual stimuli,
such as dressed men and women, will not be as strong as responses elicited with explicit
sexual stimuli. Sex differences in viewing time and gaze fixation are stronger with
explicit sexual stimuli than with non-explicit sexual stimuli, although sex differences can
still be elicited with non-explicit sexual stimuli (Aboyoun & Dabbs, 1998; Ebsworth &
Lalumière, 2012; Lykins, Meana, & Kambe, 2006; Lykins, Meana, & Strauss, 2008).
Similarly, sex and sexual orientation differences in pupil dilation may be stronger with
explicit than non-explicit sexual stimuli.
Based on the reviewed literature, the following predictions were tested:
Prediction 1
Pupil dilation to explicit sexual stimuli depicting males or females will relate to
pupil dilation to corresponding non-explicit sexual stimuli.
Prediction 2
For both explicit and non-explicit sexual stimuli, the correspondence of pupil
dilation to male or female sexual stimuli with self-reported sexual orientation will be
stronger in men than women.
Prediction 3
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Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
For both explicit and non-explicit sexual stimuli, the concordance of pupil dilation
to sexual stimuli with time spent viewing these stimuli and self-reported sexual attraction
to these stimuli will be stronger in men than women.
Prediction 4
For both explicit and non-explicit sexual stimuli, the relationships of pupil dilation
with self-reported sexual orientation, viewing time of stimuli, and self-reported sexual
attraction to these stimuli will be significant, although stronger for explicit than non-
explicit sexual stimuli.
Method
Participants
The recruitment period was from October 2010 to June 2011. Advertisements were
placed on several websites at a Northeast university in the USA. In addition,
advertisements for bisexual men were placed at local web forums where men sought
sexual encounters with either men, women, or both. The method is efficient for recruiting
bisexual-identified men, who are less common than other men (Rosenthal, Sylva, Safron,
& Bailey, 2012). The 165 recruited men self-identified as “exclusively straight” (n = 31),
“mostly straight” (n = 24), “bisexual leaning straight” (n = 15), “bisexual” (n = 10),
“bisexual leaning gay” (n = 21), “mostly gay” (n = 33), and “exclusively gay” (n = 31).
The 160 recruited women self-identified as “exclusively straight” (n = 34), “mostly
straight” (n = 27), “bisexual leaning straight” (n = 11), “bisexual” (n = 17), “bisexual
leaning lesbian” (n = 16), “mostly lesbian” (n = 32), and “exclusively lesbian” (n = 23).
The average age (SD) was 23.36 (6.62) years in men and 27.70 (6.78) years in women.
The most common ethnicity was Caucasian in men (64%) and women (69%). Mixed
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Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
ethnicities were second most common across men and women (10%), followed by Asian,
African-American, Hispanic, and Native-American. For these participants, results for
pupil dilation patterns to explicit sexual stimuli have been previously published (Rieger
& Savin-Williams, 2012), but findings for non-explicit sexual stimuli and a comparison
of pupil dilation patterns to the two types of stimuli have not been reported.
Measures
Sexual orientation. Participants reported their aforementioned sexual orientation
identities, in addition to their sexual attractions, sexual fantasies, and sexual infatuations
(i.e., passions for men or women) on Kinsey-type scales (Kinsey, Pomeroy, & Martin,
1948). For example, for sexual attraction, participants endorsed one of seven statements
ranging from “ 0 = exclusively attracted to the females”, to “3 = equal attraction to
females and males,” to “6 = exclusively attracted to males.” The four measures were
correlated in men (all p’s <. 0001, all r’s > .95, .92 < CI’s > .99) and women (all p’s <.
0001, all r’s > .92, .89 < CI’s > .96), and averaged within participants. An average score
of 0 represented an exclusively heterosexual orientation and an average score of 6 an
exclusively homosexual orientation.
Stimuli. Each stimulus was a 30-second video of similar luminance. Twelve
sexually explicit male stimuli and 12 sexually explicit female stimuli depicted a full body
shot of either a naked male or female model, alone in a room, sexually aroused, and
masturbating. These stimuli were selected from a pool of 200 videos drawn from sites on
the Internet. In a pilot study, heterosexual and homosexual men and women rated these
videos on the models’ sexual appeal, and those stimuli that were rated highest across all
groups were used for this study.
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Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
The 12 non-explicit male and 12 non-explicit female stimuli depicted men and
women who were casually dressed, in full view, and seated in a chair discussing winters
in North America. Their answers were given to the interviewer who was standing behind
the camera. These men and women were originally interviewed at a Midwestern
university in the USA. In total there were 185 non-explicit sexual stimuli whose
attractiveness has been previously assessed (Rieger et al., 2011), and the most attractive
men and women were used in the present study. The average age (SD) was 21.67 (1.72)
years and 22.83 (3.83) years, respectively. The most common ethnicity was Caucasian
with 67% and 58%, respectively.
Two 1-minute videos of landscapes, taken from nature documentaries, were used as
neutral stimuli.
Pupil data. An SR Research Remote infrared gaze tracker recorded participants’
eyes. The gaze tracker collected data every two milliseconds with a 16 mm lens focused
on participants’ preferred eye. Participants’ heads rested on a mount 500 mm from the
lens, and the head’s exact position was automatically recorded by measuring the distance
in mm from the lens to a reference point affixed to the forehead. The program EyeLink
computed pupil area as the number of the tracker’s camera pixels occluded by the
infrared light reflected by the pupil. If pupils dilated while viewing stimuli, more pixels
were occluded.
Viewing time. Viewing time was captured with the SR Research gaze tracker, and
calculated as the percentage of time looking at a male or female sexual stimulus.
Procedure
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Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
After giving written informed consent, participants took seat in a dimly lit room
facing the gaze tracker underneath a monitor with a screen resolution of 1024 by 768
pixels. Stimuli were presented in two modules, the first of which was used for recording
pupil dilation data. Participants watched a neutral stimulus, followed, in random order, by
the sexual stimuli. Participants randomly watched either all the explicit sexual stimuli
first or all the non-explicit sexual stimuli first. After each stimulus, participants answered
three questions in random order, regarding how sexually attractive they found the person,
how sexually appealing they found the person, and how much they would like to date the
person. These questions were displayed across the screen and participants used a mouse
to give their answers. Participants responded to each question with a 7-point scale
ranging from “not at all” to “average,” to “very much.” Immediately after they answered
the last question, the next stimulus was presented.
The second module started with another neutral stimulus. Then, two stimuli were
presented simultaneously. Half of these paired stimuli showed the male to the right of the
female; the other half showed the male to the left of the female. Participants were free to
choose how much time they wanted to spend on viewing either of the paired stimuli.
Participants watched either all paired explicit sexual stimuli first, or all paired non-
explicit sexual stimuli first. For each type of stimulus, paired stimuli were shown in
random order. This module was chosen for the collection of data regarding time spent
viewing male or female stimuli. After each stimulus pair, participants answered three
questions that were, in random order, displayed across the screen. They responded to
which of the two people they found more sexually attractive, more sexually appealing,
and would more like to date. Answers were given on 7-point scales ranging from “very
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Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
much the left,” to “equal,” to “very much the right.” Because a male stimulus could be
either to the left or right of a female stimulus, we considered it would be easier for
participants to indicate on which side the more attractive model was, rather than stating
that they were more attracted to the “male” or “female.”
For each module, participants eye movements were continuously monitored in a
control room with a screen that showed the stimuli participants were viewing, with the
position of their pupil superimposed on it. In the rare cases that participants looked away
from the screen, they were instructed through an intercom that they should watch every
video carefully, no matter if they liked the content or not. Other than that participants
were free to view any part of the screen as they wished.
After the experiment, participants completed a survey with demographic
information and sexual orientation and received payment. The procedure took
approximately 45 minutes.
Data Reduction
For each participant and for each stimulus, pupil size data were averaged by
dividing the total of occluded camera pixels across data points by the number of data
points (which were collected every two milliseconds). Similarly, for each participant and
stimulus, we calculated average head distance by dividing the total of head distance (in
mm) across data points by the number of data points. Averaged pupil size was multiplied
with averaged head distance for each stimulus, to account for some head movements
between stimuli. For further standardization of data, we followed procedures that yield
predicted sex and sexual orientation differences in pupil dilation data (Rieger et al.,
2015a), and that mirror recommendations for analyzing genital arousal responses (Harris,
12
Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
Rice, Quinsey, Chaplin, & Earls, 1992). Because pupils vary in size and level of dilation,
we computed within each participant z-scores of pupillary response to each stimulus. We
then calculated, for each participant, five mean values, one each for average pupil dilation
to explicit male sexual stimuli, explicit female sexual stimuli, non-explicit male sexual
stimuli, non-explicit female sexual stimuli, and neutral stimuli. For analyses of pupil
dilation to explicit and non-explicit sexual stimuli, responses to neutral stimuli were
subtracted. Hence, these variables indicated changes of pupil dilation to sexual stimuli as
compared to neutral.
For viewing time, a score of 50% indicated equal time spent viewing the same sex
and other sex, larger values indicated higher percentage of time viewing the same sex
than the other sex, and lower values indicated the opposite. These percentages were
reliable across paired explicit sexual stimuli and across paired non-explicit sexual stimuli
(Cronbach’s
> .92 in both sexes). They were averaged within participants and
separately for each stimulus type (i.e., explicit and non-explicit sexual stimuli).
For both explicit and non-explicit sexual stimuli, participants’ three ratings were
reliable within each stimulus, across all male stimuli, across all female stimuli, and across
all paired male-female stimuli, (all r’s > .88; all Cronbach’s
’s > .93). For each
participant and each stimulus type, an average was computed across ratings. For both
explicit and non-explicit sexual stimuli collected during the first module, these averages
represented self-reported sexual attraction to stimuli of the same sex, sexual attraction to
stimuli of the other sex, and, from the second module, a contrast of sexual attraction to
the same sex over the other sex.
Results
13
Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
Prediction 1
The first prediction states that pupil dilation to explicit sexual stimuli relates to
pupil dilation to corresponding non-explicit sexual stimuli. In men, there were small to
modest correlations between pupil dilation to explicit and matching non-explicit sexual
stimuli. This was the case for the correlation between responses to explicit and non-
explicit sexual stimuli of the same sex, p = .03, r = .18, 95% CI [.02, .32], the correlation
between responses to explicit and non-explicit sexual stimuli of the other sex, p < .0001,
r = .40, 95% CI [.26, .52], and the correlation of a contrast for explicit sexual stimuli
(responses to the same sex minus the other sex) with such contrast for non-explicit sexual
stimuli, p < .0001, r = .31, 95% CI [.17, .44]. (From here on we omit the phrase “95%
CI.” Instead, we simply report numbers is squared brackets to the right of an effect size in
order to represent its 95% confidence intervals). In women, these correlations were
similar in magnitude, p < .0001, r = .35 [.21, .48], p = .02, r = .16 [.01, .31], and p = .001,
r = .25 [.11, .39], respectively. Hence, dilation to sexual stimuli somewhat resembled
dilation to non-sexual stimuli. These correlations pointed to the possibility that each of
these measures – dilation to explicit and non-explicit sexual stimuli – had similar
relations with sexual orientation.
Prediction 2
The second prediction states that the correspondence of pupil dilation to same-sex
or other-sex stimuli with self-reported sexual orientation is stronger in men than women.
We tested this prediction separately for explicit and non-explicit sexual stimuli.
Explicit Sexual Stimuli. In both men and women, pupil dilation to explicit sexual
stimuli of the same sex correlated strongly and negatively with dilation to explicit sexual
14
Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
stimuli of the other sex, p < .0001, r = -.82 [-.87, -.76], and p < .0001, r = -.77 [-.82,
-.69], respectively. We therefore computed a contrast score. Positive numbers resembled
more dilation to the same sex than other sex, negative numbers resembled more dilation
to the other sex than same sex, and zero indicating equal dilation to both sexes. We
regressed this contrast onto self-reported sexual orientation. Independent variables
included both the linear and quadratic function of sexual orientation because these
relations can be, to some degree, curvilinear (Rieger et al., 2013; Rieger et al., 2015b).
Figure 1A shows that for men, the linear relationship (but not the curvilinear
relationship) of pupil dilation to the same sex or other sex with sexual orientation was
significant, p < .0001,
= .54 [.40, .67]. (The effect size
is the standardized regression
coefficient that can be interpreted similarly to a correlation coefficient.) Heterosexual
men dilated most to the other sex, bisexual men dilated approximately equally to both
sexes, and homosexual men dilated most to the same sex.
In women, pupil dilation to the same or other sex also related to their sexual
orientation in a linear fashion, p < .0001,
= .44 [.31, .59]. This linear relationship was
qualified by quadratic effect, although not significantly so, p = .08,
= .13 [-.08, .34]. In
Figure 1B, this quadratic effect can be explained by the position of the coefficient’s 95%
confidence intervals relative to a dilation contrast score of zero (which stands for equal
dilation). Exclusively heterosexual women dilated more to the other sex than to the same
sex; however, in comparison, exclusively homosexual women dilated more strongly to
the same sex than the other sex.
Figure 1
15
Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
A multiple regression analysis tested for sex differences in the above findings. Pupil
dilation to the same sex or other sex was predicted by the linear and curvilinear effects of
sexual orientation, by participants’ sex, and the interactions of the linear and curvilinear
effects of sexual orientation with sex. These interactions examined whether the sexes
differed in these linear and curvilinear effects. Results indicated no significant sex
difference for the linear relation of pupil dilation with sexual orientation, p = .35,
= -.04
[-.14, .06]. In magnitude, the sex difference for the curvilinear relationship was stronger
than for the linear relationship, but it, too, was not significant, p = .08,
= .16 [-.01, .28].
If anything, the curvilinear relationship of pupil dilation patterns with sexual orientation
was more common in women than men (Figure 1).
Figure 1 illustrates a further sex difference for exclusively heterosexual men and
women (Kinsey Score of 0). These heterosexual men dilated more strongly to the other
sex than the same sex, compared with heterosexual women. An independent-sample t-
test, comparing these men and women for dilation to the other sex over the same sex,
suggested a significant sex difference in effect, p = .0001, Cohen’s d = 1.07 [.81, 1.31].
Non-Explicit Sexual Stimuli. We repeated aforementioned analyses with non-
explicit sexual stimuli. For men, pupil dilation to the same sex correlated significantly
and negatively with dilation to the other sex, p = .009, r = -.20 [-.35, -.05]. For women,
this correlation was similar in magnitude, but it was not significant, p = .09, r = -.14 [-.28,
.02]. A multiple regression analysis indicated that across men and women this
relationship was significant and negative, p = .002,
= -.17 [-.29, -.06], and that men and
women did not significantly differ in effect, p = .54,
= -.03 [-.15, .30].
16
Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
These effects were much weaker than in the previous analyses on explicit sexual
stimuli. For comparison with the contrast score calculated for explicit sexual stimuli
(Figure 1), we computed a corresponding contrast for non-explicit sexual stimuli by
subtracting dilation to the other sex from dilation to the same sex. This contrast correlated
slightly better with self-reported sexual orientation than either of its components
(compare Figure 2 with Table 2). Moreover, this relation of pupil dilation to the same sex
or other sex with sexual orientation was linear and significant in both men and women; p
< .0001,
= .46 [.32, .61], and p < .0001,
= .41 [27. 56], respectively. Heterosexual
men and women dilated somewhat more to the other sex than the same sex, bisexual
participants showed equal dilation, and homosexual men and women dilated more to the
same sex than other sex. The curvilinear effects of sexual orientation on pupil dilation
were not significant (Figure 2).
Figure 2
A multiple regression analysis did not confirm that the sexes differed significantly
in the above effects, neither for the linear relation of pupil dilation with sexual
orientation, p = .63,
= -.03 [-.13, .08], nor for the curvilinear relationship of pupil
dilation with sexual orientation, p = .88,
= .01 [-.15, .17]. Furthermore, exclusively
heterosexual men did not show significantly more pupil dilation to the other sex than the
same sex, compared with exclusively heterosexual women, p = .25, Cohen’s d = .31
[.06, .55]. Thus, the correspondence of dilation patterns to non-explicit sexual stimuli
with sexual orientation, as illustrated in Figure 2, was similar across men and women.
Prediction 3
17
Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
We predicted that for both explicit and non-explicit sexual stimuli, pupil dilation
would relate to time spent viewing stimuli and self-reported sexual attraction to stimuli.
Furthermore, these correspondences would be stronger in men than women.
Explicit sexual stimuli. Table 1 shows the correlations across pupil dilation to the
same sex and other sex, viewing time of same-sex or other-sex stimuli, self-reported
sexual attraction towards stimuli, and of self-reported sexual orientation. Overall, these
correlations were modest to strong in effect, suggesting that pupil dilation is a reliable
indicator of sexual attraction, viewing time, and sexual orientation. All correlations were
significant, with the exception of the correlation between self-reported sexual attraction
to same-sex stimuli and other sex-stimuli for women.
Table 1
The average absolute correlation was .64 and .53 in men and women, respectively.
We then computed the difference between men and women for each correlation (within
pairs of variables) and tested the average of these difference scores against 0 by
conducting a repeated-measures t-test. The sex difference was significant, p < .0001,
Cohen’s d = 1.96 [1.66, 2.27]. (In the case of these repeated-measures t-tests, d was
calculated by dividing the average of correlation difference scores by its standard
deviation). In a second step, we excluded all correlations with sexual orientation (Table 1)
from these calculations, because sexual orientation was, unlike the other variables, not a
measure of immediate responses to stimuli. The average absolute correlations remained
similar to the above, with .60 in men and .49 in women. This sex difference was also
significant, p < .0001, Cohen’s d = 1.78 [1.42, 2.14].
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Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
Non-Explicit sexual stimuli. Table 2 shows correlations as discussed in the last
section, but in this case for non-explicit sexual stimuli. In contrast to correlations for
explicit sexual stimuli (Table 1) correlations for non-explicit sexual stimuli varied more
strongly in magnitude. Still, the majority of these correlations were significant.
Exceptions were the correlation between self-reported sexual attraction to same-sex
stimuli and other sex-stimuli for men, and the three correlations between pupil dilation to
the other sex, self-reported sexual attraction to the same sex, and self-reported sexual
attraction to the other sex for women.
Table 2
For non-explicit sexual stimuli, the average absolute correlation was .47 in men and
.41 in women. This difference was weaker than in analyses for explicit sexual stimuli, but
still significant, p = .009, Cohen’s d = 0.62 [0.25, 0.96]. Once correlations with sexual
orientation (Table 2) were excluded from these calculations, then the respective average
absolute correlations were .41 and .34; this difference was still significant, p = .03,
Cohen’s d = 0.68 [0.32, 1.04].
Prediction 4
We predicted that the relationships of pupil dilation patterns with sexual orientation,
viewing time, and self-reported attraction to stimuli would be significant with both
explicit and non-explicit sexual stimuli, but that these effects would be stronger for
explicit sexual stimuli than non-explicit sexual stimuli. For the relationship of pupil
dilation with sexual orientation, we compared effects for explicit and non-explicit sexual
stimuli as depicted in Figures 1 and 2. For the relationship of pupil dilation with viewing
19
Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
time and self-reported attraction to stimuli, we compared effects for explicit and non-
explicit sexual stimuli as shown in Tables 1 and 2.
Figures 1 and 2 illustrate that the linear relationship of pupil dilation to the same sex
or other sex with self-reported sexual orientation was somewhat smaller for non-explicit
sexual stimuli than explicit sexual stimuli. Repeated measures regression analyses
indicated that this difference in effect was significant in men, p = .046,
= .16 [.00, .31],
and not significant in women, p = .14,
= .12 [-.04, .27]. We then conducted a multiple
regression analysis. The dependent variable was the difference between explicit and non-
explicit sexual stimuli with respect to dilation to the same sex or other sex. Independent
variables were the participants’ sexual orientation, sex, and their interaction. The non-
significant interaction suggested that there was no reliable sex difference in effect, p = .
72,
= -.02 [-.13, .09], and across all men and women, pupil dilation to the same sex over
other sex was more strongly related to sexual orientation with explicit sexual stimuli than
non-explicit sexual stimuli, p = .01,
= .14 [.03, .25].
Figures 1 and 2 further illustrate that the most diminished response to non-explicit
sexual stimuli (compared with explicit sexual stimuli) was for exclusively heterosexual
men. We tested with an additional regression analysis whether the diminished effect was
more substantial for exclusively heterosexual men than for other participants. Although
this difference in effect was not significant, p = .27,
= .14 [-.06, .27], it may still be
meaningful, as we will discuss below.
Tables 1 and 2 show that, in general, correlations of pupil dilation with all viewing
time, self-reported sexual attraction, and self-reported sexual orientation were stronger in
magnitude with explicit sexual stimuli than with non-explicit sexual stimuli. For both
20
Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
men and women, we computed the difference in absolute correlations between explicit
and non-explicit sexual stimuli (within pairs of variables) and tested these difference
scores against 0 with a repeated-measures t-test. In men, these correlations with explicit
sexual stimuli were significantly stronger than correlations with non-explicit sexual
stimuli, p < .0001, Cohen’s d = 1.52 [1.22, 1.82]. A similar difference was found in
women, p = .001, Cohen’s d = 0.79 [0.48, 1.09]. When correlations with sexual
orientation were excluded, the average absolute correlation was also stronger with
explicit sexual stimuli than non-explicit sexual stimuli, both for men, p < .0001, Cohen’s
d = 1.42 [1.06, 1.78], and for women, p = .004, Cohen’s d = 0.92 [0.56, 1.23].
Discussion
Findings of the present study suggest that a) pupil dilation to explicit and non-
explicit sexual stimuli was related, although this relationship was modest at best, b)
sexual orientation differences were found with both types of stimuli, however, some sex
differences were only detected with explicit but not with non-explicit sexual stimuli, and
c) pupil dilation patterns were weaker with non-explicit sexual stimuli than explicit
sexual stimuli.
Explicit and Non-Explicit Sexual Stimuli
Prediction 1 was confirmed in the sense that significant links in responses to
explicit sexual stimuli and corresponding non-explicit sexual stimuli were found in the
data. Yet, these links were weak to modest in magnitude, suggesting that pupil dilation to
non-explicit sexual stimuli can only to a limited degree be interpreted as a reflection of
pupil dilation to explicit sexual stimuli. This suggests that either type of sexual stimulus
(explicit or non-explicit) can relate to any other variable (such as sex or sexual
orientation) in somewhat different manners. This discrepancy could, in part, explain why
21
Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
sex differences in the relation of sexual orientation with pupil dilation to explicit sexual
stimuli were not reflected in corresponding sex differences with non-explicit sexual
stimuli.
To be certain, Predictions 2 and 3, regarding sex differences in the correspondences
of pupil dilation with sexual orientation, viewing time, and self-reported attraction to
stimuli were broadly confirmed: overall, these effects were stronger for men than for
women (Figures 1 & 2, Tables & 2). The one exception was that with non-explicit sexual
stimuli, the link between sexual orientation and pupil dilation to the same sex or other sex
was not significantly stronger in men than women. This was contrarily to Prediction 2.
Notably, Figures 1 and 2 indicate that the most visual decrease in dilation from explicit
and non-explicit sexual stimuli was for exclusively heterosexual men. This decrease made
their dilation patterns to non-explicit sexual stimuli similar, in magnitude, to the dilation
patterns of heterosexual women. Although this change was not significantly stronger in
heterosexual men than other participants, it may have some meaning. Heterosexual men
might be particularly focused on signals of female proceptivity (Mishra, Clark, & Daly,
2007), which are likely more readily observed in nude women than dressed women. The
lack of such information in non-explicit sexual stimuli could have led to a decrease in
heterosexual men’s arousal patterns, resulting in an overall non-significant sex difference
in the effect of sexual orientation on pupil dilation with non-explicit sexual stimuli.
Prediction 4 was that the correspondences of pupil dilation with sexual orientation,
viewing time, and self-reported attraction would be weaker with non-explicit sexual
stimuli than with explicit sexual stimuli. Such differences in effect were generally
confirmed. With respect to sexual orientation, though, Figures 1 and 2 illustrate that these
22
Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
effects were not drastically weaker for non-explicit sexual stimuli than explicit sexual
stimuli. Hence, the more important conclusion may be that for both men and women, it
was still possible to provoke pupillary responses with non-explicit sexual stimuli that
were indicative of their sexual orientation.
It is possible that any predicted differences in pupil dilation between and within the
sexes will become larger in effect with refined methodologies. For example, at least for
men and with explicit sexual stimuli, longer videos (3 minutes) elicit much stronger links
between their pupil dilation patterns and sexual orientation than the 30s videos used in
the present research (Rieger et al., 2015a). Non-explicit videos of 3 minutes could also
yield stronger effects than presently reported, and possibly reveal differences in responses
to non-explicit sexual stimuli that were not detected in the current study.
Further research should examine the within-participant relationship between pupil
dilation to non-explicit sexual stimuli with genital responses to explicit sexual stimuli.
Such a method will aid in directly testing the prediction that pupillary responses to subtle
sexual stimuli can be a reflection of genital arousal to explicit sexual stimuli.
Furthermore, in qualitative interviews some of our participants stated that they felt more
drawn to the non-explicit sexual stimuli than the explicit sexual stimuli, because unlike
the latter, the first represented realistic romantic and sexual partners they could
potentially meet (Savin-Williams, 2016). Examining features other than physical
attractiveness that make non-explicit sexual stimuli sexually or romantically appealing
could enhance any relationships of the perceivers’ sexual orientation with their pupil
responses.
Limitations
23
Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
The presentation of stimuli was random for each set (explicit or non-explicit sexual
stimuli). Hence, at the onset of stimulus presentation, each stimulus had the same chance
to appear in any given order. Still, by chance, certain stimuli might have been presented
earlier than others, on average, which could have affected results. However, we consider
this possibility very unlikely. For each participant, the chance that a given stimulus was
first in order was 1/12 = .08. For the same stimulus to always be first in order across all
325 participants was .08 to the power of 325, which approximates zero. The chance that
any two or more stimuli were always in the same order across all participants is even less.
Similarly, the fact that some participants viewed explicit sexual stimuli before non-
explicit sexual stimuli, or vice versa, could have affected their responses. However, the
random presentation with the large number of participants should balance out any order
effects.
Another limitation was that each stimulus was presented immediately after the
questions for the previous stimulus; thus, undesired carry-over effects such as cognitive
load could have affected pupillary response to subsequent stimuli. For this reason, we
have previously reported analyses for explicit sexual stimuli that were restricted to the
last 10 seconds of each stimulus. Any correlations with other variables (such as sexual
orientation) were virtually identical, regardless of whether the full length of stimuli or
their last 10 seconds were used for analyses (Rieger & Savin-Williams, 2012). Likewise,
results were virtually identical, regardless of whether pupil data for non-explicit sexual
stimuli were restricted to the last 10 seconds or not. Hence, it is unlikely that carry-over
effects influenced results. Still, a refined methodology could avoid these limitations, for
24
Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
example by presenting neutral stimuli between sexual stimuli, therefore facilitating a
return to baseline before the next sexual stimulus (Rieger et al., 2015a).
Conclusion
These potential methodological improvements aside, the present data support the
proposal that the assessment of pupil dilation can be combined with non-explicit sexual
stimuli for fully non-invasive studies on sexual attraction and arousal (Rieger & Savin-
Williams, 2012). Such a design has advantages. For example, in several traditional
cultures it is impossible to assess physiological genital arousal or to show footage that is
highly graphic and sexual in content. For this reason, little is understood about the
physiological sexual arousal patterns outside of Westernized societies. For instance,
globally and through history, there have been men and women who do not adopt
stereotypical male or female identities (Mirandé, 2015; Nanda, 1986; Young, 2000). The
degree to which their identities reflect unique sexual arousal patterns is largely unknown.
One such group is found in the Polynesian population of Samoa. Recent research in this
population on men with varied sexual identities has used viewing time paradigms in order
to examine cultural differences in attention and attraction to non-explicit sexual stimuli
(Petterson, Dixson, Little, & Vasey, 2015, 2016). Because viewing time can be to some
level under the conscious control of participants (Johnson, 1995; Munoz & Everling,
2004), using the additional assessment of pupil dilation to stimuli in such societies could
give further insight into the automatic expression of universally similar or culturally
distinct sexual attraction and arousal patterns.
25
Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
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Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli 33
Correlations between Pupil Dilation, Viewing Time, Self-Reported Attraction to Explicit Sexual Stimuli, and Self-Reported Sexual Orientation across
Male (N = 165, above Diagonal) and Female (N = 160, below Diagonal) Participants.
Measure Pupil Dilation
To Same Sex
Pupil Dilation
To Other Sex
Viewing
Time1
Attraction to
Same Sex
Stimuli
Attraction to
Other Sex
Stimuli
Sexual
Attraction
Contrast1Orientation
Pupil Dilation To Same Sex -.82***
[-.87, -.76]
.50***
[.37, .60]
.45***
[.32, .56]
-.38***
[-.51, -.25]
.52***
[.39, .62]
Pupil Dilation To Other Sex -.77***
[-.82, -.69]
-.53***
[-.63, -.41]
-.44***
[-.56, -.31]
.43***
[.29, .54]
-.55***
[-.65, -.44] [-.64, .43]
Viewing Time1.41***
[.27, .53]
-.48***
[-.59, -.35]
.77***
[.69, .83]
-.74***
[-.80, -.66]
.93***
[.91, .95]
Sexual Attraction to Same Sex .29**
[.14, .43]
-.39***
[-.51, -.25]
.69***
[.59, .76]
-.35***
[-.48, -.21]
.80***
[.74, .85]
Sexual Attraction to Other Sex -.33***
[-.46, -.18]
.29**
[.14, .43]
-.58***
[-.67, -.46]
-.14
[-.29, .01]
-.77***
[-.83, -.70] [-.82, -.69]
Sexual Attraction Contrast1.33***
[.19, .47]
-.42***
[-.54, -.29]
.89***
[.85, .92]
.76***
[.69, .82]
-.61***
[-.70, -.50]
Sexual Orientation1.39***
[.25, .52]
-.44***
[-.56, -.31]
.82***
[.76, .87]
.67***
[.57, .75]
-.60***
[-.69, -.50]
.90***
[.86, .92]
Numbers in brackets represent 95% confidence intervals. 1Higher scores indicate stronger response or orientation to the same sex and less to the
p < .10. **p < .001. ***p < .0001.
Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli 34
Correlations between Pupil Dilation, Viewing Time, Self-Reported Attraction to Non-Explicit Sexual Stimuli, and Self-Reported Sexual Orientation
across Male (N = 165, above Diagonal) and Female (N = 160, below Diagonal) Participants.
Measure Pupil Dilation
To Same Sex
Pupil Dilation
To Other Sex
Viewing
Time1
Attraction to
Same Sex
Stimuli
Attraction to
Other Sex
Stimuli
Sexual
Attraction
Contrast1Orientation
Pupil Dilation To Same Sex -.20*
[-.35, -.05]
.22*
[.07, .36]
.28**
[.13, .41]
-.25**
[-.38, -.10]
.31***
[.16, .44]
Pupil Dilation To Other Sex -.14
[-.28, .02]
-.37***
[-.50, -.23]
-.29**
[-.42, -.14]
.31***
[.16, .44]
-.38***
[-.51, -.24] [-.53, -.28]
Viewing Time1.29**
[.14, .43]
-.22*
[-.37, -.07]
.56***
[.44, .66]
-.62***
[-.71, -.52]
.81***
[.75, .86]
Sexual Attraction to Same Sex .25*
[.10, .39]
-.09
[-.24, .07]
.62***
[.51, .71]
-.14
[-.29, .01]
.70***
[.61, .77]
Sexual Attraction to Other Sex -.24*
[-.38, -.09]
.12
[-.03, .27]
-.44***
[-.56, -.31]
-.13
[-.28, .02]
-.71***
[-.78, -.62] [-.77, -.61]
Sexual Attraction Contrast1.34***
[.19, .47]
-.18*
[-.33, -.03]
.78***
[.71, .83]
.78***
[.71, .84]
-.54***
[-.64, -.42]
Sexual Orientation1.36***
[.22, .49]
-.24*
[-.39, -.09]
.69***
[.60, .77]
.67***
[.58, .75]
-.59***
[-.68, -.48]
.87***
[.83, .91]
Numbers in brackets represent 95% confidence intervals. 1Higher scores indicate stronger response or orientation to the same sex and less to the
p < .10. *p < .05. **p < .001. ***p < .0001.
Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
0 1 2 3 4 5 6
-1.5
-1
-.5
0
.5
1
1.5
Pupil Dilation To Explicit Stimuli
Male Sexual Orientation
p < .0001, β = .54 [.40, .67]
p = .64, β = -.03 [-.25, .19]
A
-1.5
-1
-.5
0
.5
1
1.5
0 1 2 3 4 5 6
Female Sexual Orientation
p < .0001, β = .44 [.31, .59]
p = .08, β = .13 [-.08, .34]
Pupil Dilation to Explicit Stimuli
B
Figure 1. Reported sexual orientation of 165 men (A) and 160 women (B) relates to pupil
dilation to explicit sexual stimuli of the same sex or the other sex. On the Y axes, positive
numbers reflect stronger responses to the same sex, and negative numbers stronger
responses to the other sex, z-scores within participants. On the X axes, 0 represents an
exclusive heterosexual orientation, 3 a bisexual orientation, and 6 an exclusive
homosexual orientation. Lines represent regression coefficients with 95% confidence
intervals. Dots represent participants’ average scores. Statistics represent linear and
curvilinear effects.
35
Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
0 1 2 3 4 5 6
-1.5
-1
-.5
0
.5
1
1.5 A
0 1 2 3 4 5 6
C
Pupil Dilation To Non-Explicit Stimuli
Pupil Dilation To Non-Explicit Stimuli
Female Sexual Orientation
p < .0001, β = .41 [.27, .56]
p = .23, β = .09 [-.12, .30]
Male Sexual Orientation
p < .0001, β = .46 [.32, .61]
p = .37, β = .07 [-.15, .31]
-1.5
-1
-.5
0
.5
1
1.5
Figure 2. Reported sexual orientation of 165 men (A) and 160 women (B) relates to pupil
dilation to non-explicit sexual stimuli of the same sex or the other sex. On the Y axes,
positive numbers reflect stronger responses to the same sex, and negative numbers
stronger responses to the other sex, z-scores within participants. On the X axes, 0
represents an exclusive heterosexual orientation, 3 a bisexual orientation, and 6 an
exclusive homosexual orientation. Lines represent regression coefficients with 95%
confidence intervals. Dots represent participants’ average scores. Statistics represent
linear and curvilinear effects.
36
... The content of sexual images in previous studies varies. They vary in this study as well: The stimuli do not only include nude couples engaged in sexual acts (Study 1), but also nude couples or individuals or nonexplicit images of dressed couples or individuals (e.g., Watts et al. 2017). To validate whether the BASIC model generalizes to different types of sexual image content, Study 2 included sexual IAPS images with content distinct from Study 1. ...
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Previous studies suggest there is a complex relationship between sexual and general affective stimulus processing, which varies across individuals and situations. We examined whether sexual and general affective processing can be distinguished at the brain level. In addition, we explored to what degree possible distinctions are generalizable across individuals and different types of sexual stimuli, and whether they are limited to the engagement of lower-level processes, such as the detection of visual features. Data on sexual images, nonsexual positive and negative images, and neutral images from Wehrum et al. (2013) (N = 100) were reanalyzed using multivariate support vector machine models to create the brain activation-based sexual image classifier (BASIC) model. This model was tested for sensitivity, specificity, and generalizability in cross-validation (N = 100) and an independent test cohort (N = 18; Kragel et al. 2019). The BASIC model showed highly accurate performance (94-100%) in classifying sexual versus neutral or nonsexual affective images in both datasets with forced choice tests. Virtual lesions and tests of individual large-scale networks (e.g., visual or attention networks) show that individual networks are neither necessary nor sufficient to classify sexual versus nonsexual stimulus processing. Thus, responses to sexual images are distributed across brain systems.
... Stimulus PC [1,9] Polt and Hess ( gender differences in pupil dilation in response to sexually arousing images: Some have found that pupil dilation is consistent with the sexual orientation of the participant (Attard-Johnson and Bindemann, 2017; Finke et al., 2017;Rieger et al., 2015;Watts et al., 2017), whereas others have not found such an effect (Aboyoun and Dabbs, 1998;Scott et al., 1967;Snowden et al., 2019). Our results are in line with Snowden et al. (2019), who reported that the pupils dilate to sexual imagery but that the dilation does not relate to a person's gender. ...
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Several papers by Eckhard Hess from the 1960s and 1970s report that the pupils dilate or constrict according to the interest value, arousing content, or mental demands of visual stimuli. However, Hess mostly used small sample sizes and undocumented luminance control. In a first experiment (N = 182) and a second preregistered experiment (N = 147), we replicated five studies of Hess using modern equipment. Our experiments (1) did not support the hypothesis of gender differences in pupil diameter change with respect to baseline (PC) when viewing stimuli of different interest value, (2) showed that solving more difficult multiplications yields a larger PC in the seconds before providing an answer and a larger maximum PC, but a smaller PC at a fixed time after the onset of the multiplication, (3) did not support the hypothesis that participants' PC mimics the pupil diameter in a pair of schematic eyes but not in single-eyed or three-eyed stimuli, (4) did not support the hypothesis of gender differences in PC when watching a video of a male trying to escape a mob, and (5) supported the hypothesis that arousing words yield a higher PC than non-arousing words. Although we did not observe consistent gender differences in PC, supplementary analyses showed gender differences in eye movements towards erogenous zones. Furthermore, PC strongly correlated with the luminance of the locations where participants looked. Overall, our replications confirm Hess' findings that pupils dilate in response to mental demands and stimuli of an arousing nature. Hess' hypotheses regarding pupil mimicry and gender differences in pupil dilation did not replicate.
... The second type of experiment in which pupil diameter may be affected by accommodation is an experiment in which two-dimensional pictorial stimuli are used for investigating pupillary response (e.g., Attard-Johnson & Bindemann, 2017;Finke, Deuter, Hengesch, & Schächinger, 2017;Mckinnon et al., 2020;Nakakoga et al., 2020;Snowden, McKinnon, Fitoussi, & Gray, 2019;Watts, Holmes, Savin-Williams, & Rieger, 2017). Such stimuli might contain monocular depth cues, which raises the question of whether apparent depth could trigger a change in accommodation or pupil diameter. ...
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Much psychological research uses pupil diameter measurements for investigating the cognitive and emotional effects of visual stimuli. A potential problem is that accommodating at a nearby point constricts the pupil. This study examined to what extent accommodation is a confounder in pupillometry research. Participants solved multiplication problems at different distances (Experiment 1) and looked at line drawings with different monocular depth cues (Experiment 2) while their pupil diameter, refraction, and vergence angle were recorded using a photorefractor. Experiment 1 showed that the pupils dilated while performing the multiplications, for all presentation distances. Pupillary constriction due to accommodation was not strong enough to override pupil dilation due to cognitive load. Experiment 2 showed that monocular depth cues caused a small shift in refraction in the expected direction. We conclude that, for the young student sample we used, pupil diameter measurements are not substantially affected by accommodation.
... First, sexually explicit materials, which have been commonly used to study adult sexuality, cannot be applied to children due to ethical and legal concerns. Instead, photos, illustrations, or videos of nonnude models may serve as an alternative (Lippa, 2012(Lippa, , 2017Watts, Holmes, Savin-Williams, & Rieger, 2017). Another possibility is to study children's eye movements in naturalistic settings using wearable eyetracking glasses, for example, at a swimming pool; a prolonged eye fixation on one person may indicate sexual interests in that person. ...
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Children’s sexuality has been a taboo subject in many societies, but its existence is undeniable. A variety of sexual behaviors such as masturbation are evident starting in early childhood. Sexual games become frequent in middle childhood, especially among girls. Cross-cultural and cross-species evidence suggests that sexual desire emerges around middle childhood, along with adrenarche, which is the early phase of puberty. However, sexuality in childhood does not always signify sexual orientation in later developmental stages. In addition, different biosocial factors appear to contribute to the development of sexuality during childhood. Taking a developmental systems perspective, this chapter synthesizes existing evidence and points out areas for future research. The substantive gaps involve examining co-acting and bidirectional processes in sexuality development, focusing on sexual agency, and recording dynamic change. Transforming research methods and fostering societal recognition of children’s sexuality may be critical for not only advancing research on sexuality development in childhood, but also improving children’s well-being.
... The second type of experiment in which pupil diameter may be affected by accommodation is an experiment in which two-dimensional pictorial stimuli are used for investigating pupillary response (e.g., Attard-Johnson & Bindemann, 2017;Finke, Deuter, Hengesch, & Schächinger, 2017;Mckinnon et al., 2020;Nakakoga et al., 2020;Snowden, McKinnon, Fitoussi, & Gray, 2019;Watts, Holmes, Savin-Williams, & Rieger, 2017). Such stimuli might contain monocular depth cues, which raises the question of whether apparent depth could trigger a change in accommodation or pupil diameter. ...
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Much psychological research uses pupil diameter measurements for investigating the cognitive and emotional effects of visual stimuli. A potential problem is that accommodating at a nearby point constricts the pupil. This study examined to what extent accommodation is a confounder in pupillometry research. Participants solved multiplication problems and looked at line drawings with monocular depth cues while their eyes were recorded using a photorefractor. The results showed that the pupils dilated, especially for hard multiplications. However, refraction changes were not large enough to explain the pupil diameter changes. The monocular depth cues caused a small shift in refraction in the expected direction. The results further suggest a link between eye movements, refraction, and pupil diameter. We conclude that, for the type of cognitive task and young student sample we used, pupil diameter measurements are not confounded by accommodation. However, the effect of eye movements in pupillometry needs further consideration.
... The association between pupil dilation and genital response (Rieger et al., 2015) supports the proposal that early attentional processing initiates genital responding. The pupillary responses of heterosexual men, homosexual men, and homosexual women have been found to correspond with self-stated sexual interests and to show stronger cue-specificity than the pupillary responses of heterosexual women (e.g., Finke et al., 2017;Rieger et al., 2015;Rieger & Savin-Williams, 2012;Watts, Holmes, Savin-Williams, & Rieger, 2017;cf. Nummenmaa, Hietanen, Santtila, & Hyönä, 2012). ...
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Research conducted in our laboratory and in other laboratories has revealed that (1) women's genital responses to visual and auditory stimuli are strongly affected by the presence of sexual cues, but that (2) specific sexual cues (e.g., gender of actors, the presence of sexual violence) often have little impact on the magnitude of the responses-that is, similar genital responses are observed to very different sexual stimuli. In addition, (3) women's genital responses do not strongly correspond with self-reported sexual partner and activity preferences, or (4) with self-reported sexual arousal during the presentation of sexual stimuli. Taken together, these facts represent a puzzle, especially considering that men's genital responses are highly affected by specific sexual cues and strongly correspond to stated preferences and self-reported sexual arousal. One hypothesis to explain female low cue-specificity and low concordance (relative to men) is the preparation hypothesis: Women's indiscriminate genital responses serve a protective function. That is, they do not indicate or necessarily promote sexual interest and motivation, but rather prepare the vaginal lumen for possible sexual activity and therefore prevent injuries that may occur as a result of penetration. We review evidence for and against this hypothesis. We conclude that the evidence is favorable but not entirely convincing, and more work is required to reach a firm conclusion. We offer directions for future research.
... However, over and continuous usage of chemicals and drugs to control the bacterial disease which leads to bacterial resistance to the particular therapeutic agents. Further, these medicinal substances accumulate in the culture organism and enter into the food chain that affects human health and the environment [6][7][8]. On the other hand, maintaining the broodstock for longer duration in captive condition affects the reproductive performance of aquatic animals due to holding stress. Further, in captive condition, acceptance of feed and assimilation of nutrition is also a major issue, resulted in malnutrition which linked to a number of abnormalities during the progress of maturation, spawning and hatching. ...
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Objective measures of sexual interest are important for research on human sexuality. There has been a resurgence in research examining pupil dilation as a potential index of sexual orientation. We carried out a meta-analytic review of studies published between 1965 and 2020 (Mdn year = 2016) measuring pupil responses to visual stimuli of adult men and women to assess sexual interest. Separate meta-analyses were performed for six sexual orientation categories. In the final analysis, 15 studies were included for heterosexual men (N = 550), 5 studies for gay men (N = 65), 4 studies for bisexual men (N = 124), 13 studies for heterosexual women (N = 403), and 3 studies for lesbian women (N = 132). Only heterosexual and gay men demonstrated discrimination in pupillary responses that was clearly in line with their sexual orientation, with greater pupil dilation to female and male stimuli, respectively. Bisexual men showed greater pupil dilation to male stimuli. Although heterosexual women exhibited larger pupils to male stimuli compared to female stimuli, the magnitude of the effect was small and non-significant. Finally, lesbian women displayed greater pupil dilation to male stimuli. Three methodological moderators were identified—the sexual explicitness of stimulus materials, the measurement technique of pupillary response, and inclusion of self-report measures of sexual interest. These meta-analyses are based on a limited number of studies and are therefore preliminary. However, the results suggest that pupillary measurement of sexual interest is promising for men and that standardization is essential to gain a better understanding of the validity of this measurement technique for sexual interest.
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Human sexual orientation is an active topic of psychological research, with much attention focused on possible underlying endocrine factors. Promising results derive from studies of animal models, “natural experiments” involving human endocrine disorders, genetic variation in hormone receptor function, and biomarkers of hormonal signaling. Here, we review the current state of evidence concerning the effects of hormones on sexual orientation. Available evidence suggests that adult hormone levels have little effect on sexual orientation in contrast with early “organizational” hormonal influences. Specifically, fluctuations in androgen levels during periods of prenatal and neonatal development may influence brain regions associated with sexual orientation.
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Purpose of Review We examine the state of scientific research on the assessment of paraphilic interests among women who have committed sexual offences. Recent Findings Research on the assessment of sexual interests in women using genital measures shows little evidence, overall, that women’s genital responses are indicative of sexual interests. Some non-genital measures of sexual interest may be a valid indicator of age interests. Very few studies have focused on women who sexually offend. Summary At this time, there is no validated measure that can be used to assess paraphilic interests among women who sexually offend. Much research is needed to determine if some measures (other than self-report) could validly assess a variety of sexual interests in women in general, and women who sexually offend in particular (e.g. interest in children, interest in sexual violence). This research is needed to determine if paraphilic interests are involved in women’s motivation for sexual offending, and to determine if such interests are predictive of sexual recidivism.
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PROLOGUE The first reports of the measurement of physiological responses during sexual activity date back to the late 1800s. For example, Mendelsohn (1896) described “pulse curves” (EKGs) during sexual intercourse. Such early explorations were followed by more systematic attempts to understand the physiology of sexual response, as exemplified by the writings of Van de Velde (1926), Dickinson (1933), and Kinsey and colleagues (Kinsey, Pomeroy, Martin, & Gebhard, 1953). The work of Masters and Johnson (1966), who observed sexual responses in over 650 individuals, served as a foundation for the field of sexual psychophysiology and continues to be the stimulus for much research. Initially, researchers relied on direct observation and the use of non-genital measures such as heart rate, respiration, and sweat gland activity to index sexual arousal. Zuckerman (1971) concluded that extragenital measures were not specific to sexual arousal. Coupled with Masters and Johnson’s (1966) report that genital vasocongestion is the most reliable indicator of sexual response, Zuckerman’s review accounts for the trend in the field toward the development and use of genital response measures. ANATOMY AND PHYSIOLOGY Anatomy Women The external female genital area is known as the vulva, which is rich in nerve endings and heavily vascularized. The labia majora, also known as the outer lips, surround the labia minora, or inner lips, which enclose an area called the vestibule. The labia minora fuse above the vestibule to form the clitoral prepuce and under the vaginal opening form the frenulum. The clitoris is composed of the clitoral head (glans), the clitoral shaft (corpus), and the clitoral legs (crura). The clitoral body consists of two corpora cavernosa. The vestibular bulbs of the crura, also referred to as the clitoral bulbs, appear homologous to the corpus spongiosum in men (O’Connell, Hutson, Anderson, & Plenter, 1998; however, see Puppo & Puppo, 2015). The clitoral shaft becomes engorged with blood during sexual arousal. However, it does not have a subalbugineal layer that would constrict venous outflow. Due to this, the clitoris can become engorged but does not reach levels of rigidity similar to that of the penis. The organ that has been the focus of genital response measurement in women is the vagina. The vagina is a collapsed canal that consists of two layers (Levin, 2003). The innermost layer is made of many transverse folds or “rugae” that provide accordion-like distensibility.
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In the visual processing of sexual content, pupil dilation is an indicator of arousal that has been linked to observers' sexual orientation. 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. These pupillary responses corresponded with observer's self-reported sexual interests and their sexual appeal ratings of the 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.
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Men’s genital responses are significantly greater to sexual stimuli of their preferred gender compared to their nonpreferred gender (gender-specific), whereas androphilic (i.e., sexually attracted to men) women’s genital responses are similar to sexual stimuli depicting either women or men (gender-nonspecific). This gendered pattern of genital response has only been demonstrated using vaginal photoplethysmography (VPP) in women and primarily penile plethysmography (PPG) in men. These measures assess different aspects of genital vasocongestion, thereby limiting comparisons between genders. Thermography is a newer sexual psychophysiology methodology that measures genital vasocongestion via temperature change and is better suited to assess sexual response between genders because the dependent measure, change in genital temperature, is similar for women and men. Further, previous studies have assessed gender specificity of sexual response across relatively short sexual stimuli, allowing only the examination of initial phases of sexual response. We examined gender specificity of sexual arousal by measuring women’s and men’s genital responses to lengthier stimuli with concurrent thermography and VPP/PPG. Gynephilic men (i.e., sexually attracted to women; n = 27) and androphilic women (n = 28) viewed 10-min films depicting men masturbating, women masturbating, and a nonsexual film, and reported feelings of sexual arousal while genital responses were assessed. Across measures, men’s sexual responses were gender-specific and women’s responses were gender-nonspecific, indicating that the gender difference in gender specificity of arousal is robust to methodology and stimulus duration. These findings replicate previous research, extend knowledge of gendered sexual response, and highlight the utility of multi-method approaches in sexual psychophysiology.
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