Fundamental information about eye tracking technology

Eye tracking is the measurement of the movements of the eye, with the purpose of recording what a subject is looking at. All of our 4 eye trackers use 'dark pupil' technology, where the gaze of the eye is tracked with an infra-red camera by identifying the pupil and the reflection of an infra-red light source on the cornea.

Eye trackers come in two varieties: 'contact' and 'remote'. With contact eye trackers the camera and light source are fixed to the head, or the head is on a chin rest to limit movements relative to the camera. In remote systems the camera and light source are in a fixed location, at some distance from the subject, enabling some head movements. Contact systems are more precise and reliable, in general.

Another important feature of an eye tracker is the sampling frequency. To be able to follow the eye during saccades the minimum frequency necessary is about 200 Hz. For 'heat maps', which map summed gaze duration by location, or for AOI dwell time analyses lower frequencies are sufficient.

All our eye trackers are able to output the x and y coordinates of the screen location the subject is looking at, and the diameter of the pupil. That last value will be 0 during a blink.