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The size of the pupil can indicate
excitement and even sexual attraction.
Whether you're gay, straight or somewhere
else on the spectrum, the truth of who
Pupil dilation is an accurate indicator of
sexual orientation, a new study finds. When
people look at erotic images and become
aroused , their pupils open up in an
unconscious reaction that could be used to
study orientation and arousal without
invasive genital measurements.
The new study is first large-scale experiment
to show that pupil dilation matches what
people report feeling turned on by, said study
researcher Ritch Savin-Williams, a
developmental psychologist at Cornell
University.
"So if a man says he's straight, his eyes are
dilating towards women," Savin-Williams told
LiveScience. "And the opposite with gay men,
their eyes are dilating to men."
The eyes have it
The link between pupil size and arousal goes
way back. In 16th-century Italy, women
would take eye drops made from the toxic
herb Belladona, which kept their pupils from
constricting and was thought to bestow a
seductive look.
In fact, Savin-Williams said, the pupils dilate
slightly in response to any exciting or
interesting stimulus, including a loved one's
face or a beautiful piece of art . The dilation
is a sign that the autonomic nervous system
— the system that controls involuntary
actions like pulse and breathing — is ramping
up.
Traditionally, researchers have studied
arousal and sexual orientation by asking
volunteers to watch erotic movies or pictures
while attached to instruments that measure
blood flow to the genitals. For men, this
involves a circumference measurement of the
penis, while women use a probe that
measures pressure change in the blood
vessels of the vaginal walls.
These measurements have drawbacks, Savin-
Williams said. Some people can suppress
their genital arousal , or simply don't have
genital responses in a laboratory
environment. And then there's the
invasiveness issue.
"Some people just don't want to be involved
in research that involves their genitals,"
Savin-Williams said.
Simply asking people if a given stimulus
turns them on or not is equally problematic,
as people may be ashamed to admit their
desires or even deny them to themselves.
It's also difficult to ask direct questions
about sexual orientation in many cultures,
Savin-Williams said. [5 Myths About Gay
People, Debunked ]
Measuring arousal
To get around these issues, Savin-Williams
and his colleague Gerulf Rieger, also of
Cornell University, turned to the pupils. They
recruited 165 men and 160 women, including
gay, straight and bisexual participants. These
volunteers watched separate one-minute
videos of a man masturbating, a woman
masturbating and neutral landscape scenes.
The videos were all matched for brightness
so that differences in light wouldn't skew the
results.
A gaze-tracking camera recorded the pupils
during these videos, measuring tiny changes
in pupil size. People also reported their own
feelings of arousal to each video.
The results showed that pupil dilation
matches the pattern seen in genital arousal
studies. In men, this pattern is generally
straightforward: Straight men respond to
sexual images of women, and gay men
respond to sexual images of men. Bisexual
men respond to both men and women.
In women, things are more complex, Savin-
Williams said. Gay women show more pupil
dilation to images of other women, similar to
the pattern seen in straight men. But straight
women dilate basically equally in response to
erotic images of both sexes, despite reporting
feelings of arousal for men and not women.
[6 Gender Myths Busted ]
This doesn't mean that all straight women
are secretly bisexual, Savin-Williams warned,
just that their subjective arousal doesn't
necessarily match their body's arousal. Sex
researchers aren't sure why this happens.
One theory is that because women have been
at risk of being raped throughout history,
they evolved to respond with lubrication to
any sexual stimulus, no matter how
unappealing. This idea holds that women
who did so were less likely to experience
trauma or infection after sexual assault,
making it more likely that they would survive
to pass on their genes.
The researchers detail their findings today
(Aug. 3) in the journal PLoS ONE. The next
step, Savin-Williams said, is to look at pupil
measurements and genital measurements at
the same time, to test how well they
correspond.
Eventually, he said, this technology could be
used to conduct cross-cultural studies of
sexuality, given that pupil dilation is universal
and doesn't depend on labels of sexual
orientation that may not translate across all
languages. The method could even be used
to help people who are confused about their
sexuality sort through their desires, Savin-
Williams said.
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