How Reliable Are Your Decisions? Pupil Size Might Predict Decision Accuracy

(Last Updated On: August 3, 2017)

How can you tell if you are making the right decision? According to one new study, your pupil size might hold the answers.

The study, published in the journal PLOS Computational Biology, suggests that larger pupil sizes predicted poorer decisions in an upcoming task. Why? The authors indicate that pupils size is an indicator of arousal states, which in turn are strong determinants of variations in perceptual decision making.

The researchers measured pupil size before each task and then monitored each volunteer’s performance on perceptual decisions-making tasks. The results revealed that a person’s state of responsiveness as measured by pupil size was a key determinant in the decisions people made. Those who were highly responsive (larger pupil size) made less reliable decisions. Those who were less responsive (smaller pupil size) made better and more accurate decisions.

The study also indicated that those who had the largest pupil size overall were also the least consistent in their decisions.

The results of this study suggest that we tend to make less reliable decisions when we are in a hyper-responsive state.

“We are constantly required to make decisions about the world we live in,” suggested Peter Murphy of Leiden University and lead author of the study. “Researchers have long known that the accuracy and reliability of such everyday decision making can be tremendously variable for different people at different times, but we understand quite little about where this variability comes from. In this study, 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. This new information could prove valuable for future research aimed at enhancing the precision of decision making in real time.”


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Murphy, P. R., Vandekerckhove, J., & Niewenhuis, S. (2014). Pupil-linked arousal determines variability in perceptual decision making. PLOS Computational Biology. DOI: 10.1371/journal.pcbi.1003854

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