Pupil size shows precision of decisions

Researchers from Leiden University have found that the precision with which people make decisions can be predicted by measuring pupil size before they are presented with any information about the decision. Their study has been published in the journal PLOS Computational Biology.

Dr Peter Murphy and colleagues measured 26 study participants’ pupil size before the beginning of a visual, choice-based task. They then monitored each participant’s subsequent performance in deciding which direction a cloud of dots was moving in - left or right. These results were combined with a simple mathematical model that described how people make decisions.

Spontaneous, moment-to-moment fluctuations in pupil size were found to predict how a selection of participants varied in their successful decision-making, with the researchers noting that pupil size is “a highly sensitive index of arousal”. A larger pupil size indicated poorer upcoming task performance, due to more variability in the decisions made once the relevant information was presented. The authors also found that certain individuals who had the largest pupils overall also tended to be the least consistent in their decisions.

“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,” Dr Murphy said.

“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,” he continued. So when hyper-responsive, our decision-making appears to be less reliable and will more likely lead to undesirable outcomes.

The researchers said the findings “pave the way for future studies aimed at augmenting the precision with which people make decisions”.