We’ve said it before and we’ll say it again: the eyes don’t lie. As with eye tracking, when we are able to understand exactly what is drawing a person’s attention, the eyes can also give us information about how the individual is reacting by measuring the size of the pupil as it dilates.

Pupil dilation can result from numerous factors including light, color, sound, memory, cognitive load, emotional arousal, and more. In controlling for the other variables, the pupil’s response to a particular stimulus reflects the individual’s emotional arousal. Large pupil dilation indicates participants are experiencing a strong emotion, while little dilation indicated limited or no emotional response.

The pupil subconsciously responds to stimuli the participant is emotionally engaged with by expanding. However, the specific emotion experienced cannot be deciphered from this reaction; the response could be positive or negative and could be a result of surprise, joy, fear or anger. The dilation represents a primal arousal stimulated by whatever the participant is viewing.

Mobile eye trackers, such as the one below use both the scene camera for viewing the world and an eye camera for following the pupil. The camera captures the precise diameter of the pupil 30 times per second and this is the measurement Eye Faster uses to understand when the pupil dilates.


Combining the standard eye tracking which follows the participant’s attention with the pupil dilation data allows us to identify areas of interest in a shelf set or on a website that cause arousal based on normalized baselines per participant. The map below is an example output of a website displaying areas of interest where pupil dilation is above or below baseline.

Pupil Dilation Map

If you’re interested in discussing pupil dilation for research purposes, contact us for a consultation.

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