Another difference between liberals and conservatives

It’s normal for people’s eyes to dilate slightly while they’re thinking. But we don’t always dilate the same way. Depending on our biases, our eyes can behave slightly differently. University of Amsterdam researchers Jan Willen de Gee, Tomas Knapen and Tobias Donner found that conservatives and liberals showed different dilation patterns.

The scientists measured pupil size at constant luminance in participants while they strained to detect a faint pattern above random noise. For each trial, the subjects had to indicate whether or not the pattern was present by pressing a ‘yes’ or ‘no’ button. The images were calibrated for each subject’s eyesight so that the subjects were correct about 75% of the time.  Most trails took less than three seconds, with ‘no’ choices taking longer than ‘yes’ choices, and incorrect answers taking longer than correct ones.

Everyone’s eyes dilated while they were thinking. No surprise there. However, people who identified as conservative showed a much greater difference in dilation between ‘yes’ choices and ‘no’ choices. For self-identified liberals, yes or no, right or wrong, they always dilated about the same amount. Not so for the conservatives, who had little dilation when choosing ‘no’, but lots of dilation when choosing ‘yes’ regardless of whether they were right or wrong in making that choice.

The authors speculate that conservatives find saying ‘yes’ about something more effortful than liberals do. No comment.

de Gee JW, Knapen T, & Donner TH (2014). Decision-related pupil dilation reflects upcoming choice and individual bias. Proceedings of the National Academy of Sciences of the United States of America PMID: 24449874.