An eye
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A while back, someone remarked in passing that a mutual friend had “such beautiful blue eyes.” I was surprised—and a bit embarrassed—to realize that in all the years I’d known the woman in question, I had never noticed the color of her eyes. In North America, social convention dictates that we look someone directly in the eye while conversing, so failing to register my friend’s eye color implied that my communication skills were faulty too. But if I can be forgiven for ignoring the iris, the pupil is something that clearly deserves a great deal of attention, because it can tell us much more than the words someone speaks.

Size Matters

Would you believe that medical science has come up with two different words that mean “the measurement of pupil diameter”? It’s true. The general term, pupillometry, refers to any pupil measurement—usually performed using infrared cameras or sensors, because visible light would cause the pupils to contract and throw off the readings. A more specific term, pupillometrics, refers to the evaluation of one’s pupil size as an indicator of interest or emotion. University of Chicago biopsychologist Eckhard Hess coined the term in 1975. Hess discovered that when someone looks at something that causes positive feelings (or even just sparks interest), the pupils dilate—whereas the pupils contract when the person looks at unpleasant or uninteresting things.

Moreover, we subconsciously pick up cues from others’ pupil sizes and use them to help us form opinions about people. Hess performed an oft-cited study in which men were shown carefully retouched photographs of women. In half the photographs, the pupils were made to appear larger than normal, and in the other half, they were smaller. The men in the study invariably perceived the women with larger pupils as being more attractive and friendlier than the very same women in photographs where they appeared to have smaller pupils. And yet, none of the men in the study could say why they found one set of women more attractive than the other.

Can pupillometrics help you to find true love? A number of books and articles suggest you can determine if the person you’re dating is truly interested in you by paying attention to their pupils while talking. If they’re consistently large, take it as a good sign. To convey the impression that you’re interested in someone else, keep the lights dim to allow your own pupils to dilate. Beware, though: pupil size can indicate interest in anything—not necessarily romance. If you’re hungry, the sight of food will make your pupils large. Be sure your date isn’t really looking at someone behind you eating an ice cream cone.

Pupils can give away even more information when examined electronically. Because your pupil’s response to light varies measurably when you’re tired, devices now being installed at checkpoints along major highways use pupil response to test whether truck drivers are too fatigued to drive safely. Pupil response has also been shown to be a surprisingly accurate indicator of drug use. Even some drugs that don’t show up in urinalysis can be detected with a 30-second pupil response test. Because pupil tests are fast, inexpensive, and noninvasive, they are being used in some correctional facilities as a pre-screening mechanism: only those who fail the test are asked for urine samples.

Look Both Ways Before Answering

Pupil size isn’t the only way your eyes communicate. The direction in which someone looks while talking can also speak volumes. As you’re probably aware, the brain is divided into two hemispheres. The left hemisphere is primarily responsible for logic and analytical thought, while the right hemisphere is where emotional and creative thinking occur. Because the right brain governs the left side of the body and vice versa, we tend to look to the left when using our right brains and to the right when using our left brains.

Recalling existing information is largely a right-brain task, which means that when we’re trying to remember something we usually look to the left. Conversely, we typically look to the right when trying to construct a description or a story, making use of the logical powers of the left brain. To make matters even more interesting, looking upward suggests that a person is using images or visual memories. Looking downward is associated with kinesthetic or emotional memories, while looking directly left or right usually means the person is processing auditory data.

I’ve read in several places that because looking to the right means a person is constructing something new, this implies lying. But I’ve also read exactly the opposite—that looking to the left suggests lying (presumably because the creative right brain is being used). Still others claim that whichever direction you associate with lying, you have to switch it if the person is left-handed! In reality, the association between gaze direction and truthfulness is a tenuous one. Making up a new sentence doesn’t necessarily involve making up a new fact, after all. And although left-handed people are slightly more likely to be right-brained than right-handed people, one’s dominant hand doesn’t necessarily have anything to do with one’s dominant brain hemisphere. All the same, law-enforcement personnel are regularly taught to take note of a suspect’s gaze direction during an interrogation. Although eye movement is much less foolproof than a polygraph, it can suggest areas in which someone is not being entirely forthcoming.

I don’t recommend accusing anyone of lying just because of a rightward glance. But it does pay to listen to what they eyes say, and to be aware of how other people may interpret your involuntary eye reactions. What you learn about your friends could be even more valuable than knowing their eye color.

Note: This is an updated version of an article that originally appeared on Interesting Thing of the Day on June 10, 2004.