The Eyes Have It: Pupil Size Can Predict Whether Or Not You’ll Make A Good Or Bad Decision

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Dialted pupils may be an indication that you'll make a poor decision. Photo courtesy of Shutterstock

You should probably avoid making big decisions if you’re disgusted, have too much on your mind, or are horny. At least that’s what the results from a recent Leiden University study suggest. These three emotions, along with many others, cause our pupils to dilate, and based on the researchers’ conclusion, decisions made when one’s pupils are dilated are less reliable and more likely to have an undesirable outcome.

The study, which is published in the online journal PLOS Computational Biology, measured the pupil size of 26 volunteers as they performed visual choice-based tasks. These tasks were designed to mimic the kinds of challenging perceptual decisions most of us encounter on a daily basis, a press release reported. Results showed that differences in pupil size predicted the favorable (or unfavorable) outcomes of the volunteers’ decisions, even before they were presented with any information. For example, larger pupil size indicated that the participant would perform worse on the future task. Those who exhibited larger pupils were also likely to be inconsistent with their decisions and make regrettable choices.

The researchers explained how it was not exactly the pupil which predicted the participants’ decision-making outcomes, but rather the state of responsiveness that the pupils indicated. “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,” said Dr. Peter Murphy, lead researcher on the study.

Dilated pupils are a sign of hyper-responsiveness, and when we are hyper-responsive our decisions tend to suffer. Pupil dilation is a by-product of the nervous system processing information, Scientific American explained. It is a common response to light but also triggered by a number of emotions, such as interest, disgust, sexual arousal, and pain. The link between pupil dilation and emotion, though recognized, is not completely understood. "Nobody really knows for sure what these changes do," said Stuart Steinhauer, director of the Biometrics Research Lab at the University of Pittsburgh School of Medicine, to the publication. Along with predicting the outcome of one's decisions, scientists have also used pupil size to measure sleepiness, racial bias, mental illness, and even depression.

The appeal of pupil study, called pupillometry, is that the eyes are so easy to observe, no technology or intensive surgery required. But this simplicity comes with limitation. We are only able to see the outcome of the response — pupil dilation — not the process.

Still, the field does have much potential. Murphy and his team expressed that they hoped their findings could help improve the precision with which we make decisions and ultimately lead us to achieve better outcomes. "This new information could prove valuable for future research aimed at enhancing the precision of decision-making in real time,” he said.

Source: Murphy PR, Vanderkerckhove J, Nieuwenhuis S. Pupil-Linked Arousal Determines Variability in Perceptual Decision Making. PLOS. 2014.

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