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How Your Eyes Give You Away

New research reveals exactly what your pupils are telling others.

If you’ve ever wondered how skilled sales professionals seem to know exactly when to turn on the turbo boosters to get you to close a deal, take a good long look in the mirror. Those two orbs staring back at you show all your cards—and thanks to a recent study in computational biology, we have a little better idea how that happens.

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Your eyes, as it turns out, are a barometer of your arousal. Yes, definitely that sort of arousal, but in this case, we mean the activation of your “arousal system”—the combination of brain and nervous system components that regulate our reactions to stimuli in our environment. And while there are other physiological “tells” that show the arousal system is activated, the eyes are the most vibrant.

That’s all well and good; there's nothing inherently off-key about being aroused, except for the fact that especially heightened arousal prior to making a decision tends to correlate with...not-so-great decisions. When we are really aroused, our pupils enlarge, and what this study found is that the larger they get, the worse the decision we make.

Participants were given a motion-discrimination task—following groups of dots across a computer monitor and making determinations about which direction the dots are moving/will move (more challenging than it sounds) while their pupil size was monitored. The results showed that people with consistently larger pupil dilations made the most erratic decisions.

Quoting the study's lead author, Peter Murphy of the Department of Psychology at Leiden University in the Netherlands:

“We show that how precise and reliable a person is in making a straightforward decision about motion can be predicted by simply measuring their pupil size. This finding suggests that the reliability with which an individual will make an upcoming decision is at least partly determined by pupil-linked arousal or alertness, and furthermore, can potentially be deciphered on the fly.”

Which brings us back to the effective sales pro. While all of us have a built-in ability to read subtle signs like pupil size, certain people are exceptionally good at it. (There’s a reason why many poker players wear sunglasses.) Sales training enhances the ability to pick up on cues that someone has entered the erratic decision-making zone. (There's also good reason to believe that natural-born manipulators, like sociopaths, are frighteningly skilled eye readers.)

These study results jibe nicely with a study from a few years back called "Choking on the Money," which offered people a cash incentive for doing well on a game of Pac Man. The researchers found that they could manipulate peoples’ decision-making ability while playing the game by increasing the cash reward. In effect, the researchers were adding high-octane fuel to the participants’ arousal systems—and predictably, the players with the most cash on the line performed the worst. In a hyperaroused state, they became “overmotivated” and couldn’t judiciously focus their attention to make the best decisions.

The ideal state of arousal when facing a decision is active but dispassionate interest. Easy enough to say, not always easy to do. This is where metacognition—our ability to mentally assume a third-person perspective and think about our thinking—becomes a major asset. Beefing up metacognitive ability serves as a buffer against thinking erratically. (For more on this, see my book Brain Changer.)

In the meantime, don't get too paranoid about your pupil size. It may be predictive of helter-skelter decision-making, but enlarged pupils don't cause us to do anything. It's just something to keep in mind in one-on-one encounters, because you never know who's reading your eyes—or how well.

The latest study was published online in PLOS Computational Biology.

You can find David DiSalvo on Twitter @neuronarrative and at his website The Daily Brain. His latest book is Brain Changer: How Harnessing Your Brain’s Power To Adapt Can Change Your Life.

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