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Look in the mirror before you make an important decision. New research reveals that the reliability of out decisions can be predicted by the size of our pupils, which are located at the center of our eyes.

After monitoring the moment-to-moment fluctuation of pupil size in laboratory participants, researchers Peter Murphy and colleagues at Leiden University found that larger pupil size predicted poorer upcoming task performance. Furthermore, people who had the largest pupils overall also tended to be the least consistent with their decisions.

Researchers judged reliability of decisions by assessing the variability in choices made once the relevant information was presented to participants.

Participants' pupil sizes were measured before each segment of experimental tasks designed to reveal decision precision.

Researchers said the latest finding suggest that our pupils could reflect our state of responsiveness. Pupil size could therefore be used to determine the variability of the decisions we make about the world. The study revealed that decision-making appears to be less sharp and more likely to lead to undesirable outcomes during hyper-responsiveness. Previous studies reveal that pupil size significantly predicts how responsive an individual is at any given moment. While, larger pupils have been linked to increased responsiveness, the latest study is the first to link pupil size to reliability of our perceptual judgments.

Researchers said the study involved 26 participants who were asked to perform visual choice-based tasks that mimic the kinds of challenging perceptual decisions frequently faced in everyday life.  

"We are constantly required to make decisions about the world we live in. 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," lead researcher Peter Murphy and colleagues at Leiden University said in a news release.

The findings are published in the journal PLOS Computational Biology.