Why pupil dilation

Subsequent research found that the pupils of more intelligent people as defined by their Scholastic Aptitude Test scores dilated less in response to cognitive tasks compared with those of lower-scoring participants, indicating more efficient use of brainpower. Scientists have since used pupillometry to assess everything from sleepiness , introversion and sexual interest to race bias , schizophrenia , moral judgment , autism and depression.

And whereas they haven't been reading people's thoughts per se, they've come pretty close. Participants were told to press a button at any point during a second interval, and their pupil sizes correlated with the timing of their decisions.

Dilation began about one second before they pressed the button and peaked one to two seconds after. But are pupils informative outside the lab? Can pupil size be used to "read" a person's intentions and feelings? According to Men's Health magazine a man can tell when it is "time to make your move" by watching his date's pupils, but some skepticism is warranted.

Other efforts to exploit pupil dilations for purposes beyond scientific research have failed. During the Cold War, Canadian government officials tried to develop a device they called the " fruit machine " to detect homosexuality among civil service employees by measuring how the pupils in their eyes responded to racy images of women and men.

The machine, which never worked, was to aid the government's purge of gay men and lesbians from the civil service and thereby purportedly reduce vulnerability to Soviet blackmail. A pupil test for sexual orientation remains as unlikely as it was in the s. Researchers at Cornell University recently showed that sexual orientation correlated with pupil dilation to erotic videos of their preferred gender, but only on average and only for male subjects.

Pupillometry also became popular in the advertising industry during the s as a way to test consumers' responses to television commercials, says Jagdish Sheth , a marketing professor at Emory University.

But the practice was eventually abandoned. Despite these limitations, pupillometry is a valuable tool for psychological research, says Pittsburgh's Steinhauer, because our eyes are easy to observe as well as provide a sensitive indicator of cognitive, emotional and sensory response. We can't monitor everything going into it. Follow on twitter at jossfong Follow Joss Fong on Twitter. Changes in emotion might cause pupil dilation. The autonomic nervous system triggers various involuntary responses during emotions, such as fear or arousal.

Some research suggests that pupil dilation is one of these involuntary responses to arousal or attraction. For example, one study recruited men and women with varying sexual orientations. The researchers played erotic videos to the participants while monitoring their pupil size.

The study found that erotic videos led to pupil dilation in the participants. The team showed that bisexual men and heterosexual women had dilated pupils in response to erotic videos that included people of either sex.

Another study, this time in the journal Evolution and Human Behavior , focused on associations between pupil dilation and sexual attraction. The researchers found that it was possible to determine sexual interest from the size and darkness of the pupils. Pupil size also appears to respond to hormonal changes. One study recruited 14 women to view arousing pictures on a computer screen on different occasions. Half of the women were taking hormonal birth control pills. Women not taking birth control pills had dilated pupils while viewing arousing pictures during ovulation.

This did not occur in women taking birth control pills. There is also some evidence to suggest that pupil dilation may indicate trust. A study in the Proceedings of the National Academy of Sciences suggests that pupil size changes play a role in trust formation. It remains unclear why pupil dilation might be involved in attraction. It could be a result of hormonal changes. However, many other factors can also affect pupil dilation.

For example, research also suggests that paying attention to something can influence pupil size. It could be easy to mistake paying attention for attraction. More research in this area will be necessary to establish whether pupil dilation is a sign of attraction or a result of other factors, such as hormones or involuntary bodily responses.

Pupil dilation occurs for a variety of reasons. Mostly, pupils change size depending on how much light is necessary for proper vision. Other factors can also influence pupil dilation, such as medication or drug use.

However, some research suggests that emotions can also influence pupil dilation, including sexual attraction. This might be due to hormonal changes. More research in this area will help determine whether or not pupil dilation is a sign of attraction. This is a rare condition where a person is born with a partially or completely absent iris, resulting in a very large "pupil.

Because there is little or no iris to regulate the amount of light entering the eye, people with aniridia are very sensitive to light. It's true — researchers have found that pupil dilation appears to correspond to adult men and women's sexual interest in other adults. But there's a catch. One recent study showed that the pupils of male subjects dilated when they viewed images of women they found sexually attractive, whereas the pupils of female subjects typically dilated in response to images of attractive men and women alike.

The study authors concluded the reason for this is unclear and that further research is warranted. If you or someone else notices you have dilated pupils or one of your pupils looks larger than the other after head trauma, seek medical attention immediately. The same is true if you experience sudden dizziness, headache, confusion, balance problems or other symptoms of a possible stroke. If you notice dilated pupils after you've started taking one of the medications noted above, call your prescribing doctor for advice.

In cases other than those described above, call your eye doctor immediately for advice if you notice your pupils are dilated — especially if it comes on suddenly. If you have dilated pupils or your pupils react slower than normal to changing light conditions, you will be more sensitive to sunlight.

Eyeglasses that darken automatically in daylight or sunglasses with polarized lenses can make your eyes feel more comfortable outdoors. Custom prosthetic contact lenses can also help reduce light sensitivity caused by dilated eyes. These lenses give the appearance of having equal pupils of normal size. Prosthetic contacts are especially beneficial for cases of aniridia and large, irregular pupils caused by trauma.

Chapter The Pupils. Benign episodic unilateral mydriasis. Clinical characteristics. November The prevalence of simple anisocoria. American Journal of Ophthalmology. July