The Frontal Cortex

Dilating Pupils and Decisions

A cool new PNAS paper from the Koch lab:

In their experiment, the researchers presented six volunteers with four types of ambiguous stimuli. The volunteers viewed or listened to the stimuli and pressed a key on a keyboard when a perceptual shift occurred. At the same time, infrared eye-tracking software measured the diameter of the subjects’ pupils.

The scientists found a significant increase in the diameter of the pupil at the instant preceding the perceptual switch. The pupil, which is about 2 mm wide in bright light, dilated by as much as 1 mm at that moment–a change that, in theory, could be noticeable to a casual observer. Koch and his colleagues also found that the more the pupil dilated, the longer the period of time before the switch from one interpretation to the other.

“The pupil is not only there to regulate light, but is linked to our emotional state. This may have evolved for us to monitor the emotional state of others, and may offer a very simple way to track decision-making in general,” says Koch.

Perhaps this is why so many poker players on the pro circuit wear dark sunglasses.


  1. #1 natural cynic
    February 29, 2008

    Is that why GWB is always beady-eyed – no changes in perception???

  2. #2 Shane
    March 9, 2008

    I temperament test dogs in animal shelters for a living. Pupil dilation is a huge indicator in testing for an individual dog’s emotional state. Dilated pupils are often paired with signs of fear, such as ears back, muscles stiffening, holding the breath, etc.
    Many of the behaviors which are correlated with dilated pupils are also correlated with decision making. For example, a dog who is panting, then suddenly stops and shuts his or her mouth must do so before biting. The sequence of pupils dilating, mouth shutting and dog freezing is generally an indicator that the dog is “deciding” whether or not he or she needs to bite – in other words, the pupils dilate during the moment a canine makes the decision between fight and flight.
    It’s really cool to see human research that could relate to what we dog trainers see in our work!

  3. #3 Mark
    April 4, 2010

    I have observed in my pack of labs, that at calm the pupil is more on the restricted side, but if I hold up a toy, or call to get their attention the pupil dialates almost instantly to full. I think it does have a relationship to emotional state, but also feel it enhances their vision, when called to alertness.

  4. #4 Mikkel Nielsen
    March 17, 2011

    Få en billig A-kasse hos – alt ligefra ASE, Lederne’s, Min-A-Kasse og mange flere. Find den billigste A-kasse, der passer bedst til dine behov. post yet!

New comments have been disabled.