Big pupils = rewarded brain?

big pupils, rewarded brain

My 2018 resolution: leaving my partner compliment notes at the breakfast table. Seeing his reaction is so rewarding that the resolution seems easy to keep. I worry though that I may run out of the big hits, making his responses harder to detect. Could neuroscience help me see how hard my compliments hit target? In this blog you’ll read whether pupil dilation is a give away of a rewarded brain.

An eye tracking experiment

Joanne van Slooten, a friend at the VU University, studies whether our eyes provide a window into the brain’s reward processing. To test whether pupil dilation is a give away of a rewarded brain, Joanne filmed her participant’s eyes with a special ‘eye tracking’ camera. Meanwhile, she let them participate in a lottery. On each trial, a color cue on a computer monitor indicated whether they had an 80% chance of winning or loosing money. This meant that in one out of five cases they received an unexpected reward or loss.

Pupil dilation can be measured with a special eye-tracking camera

Big pupils reveal a surprised brain

Joanne found that pupils dilated for unexpected outcomes. They responded in the same way to unexpected reward and loss. Thus, pupil dilation reflects surprise, not whether the surprise is positive or negative. The results are published in PLOS ONE.

Pupil dilation can be a sign of unpleasant surprise

So, when I surprise my partner, his pupils will dilate. Even though this won’t tell me whether the surprise was pleasant, peaking on his astonishment still seems worthwhile.

Could I see the changes in pupil size with my bare eye? Probably, they are too small to notice. That does not mean that the brain is oblivious to someone else’s pupil dilation. Pupil size may affect social judgment on an ‘implicit’ level that you are not aware of. Already in 1975, the American Psychologist Eckhard Hess proposed in Scientific American that pupil dilation affects social judgment. When he showed men two versions of a woman’s picture, one with enlarged pupils and one with normal pupils and asked them in which version the woman appeared more sympathetic, the men tended to point towards the version with big pupils.

Do you want to try the pupil trick on your selfie’s? Check this Photoshop tutorial.

Next up: do your eye blinks reflect your reward sensitivity?

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