Eye tracking is a technique used in cognitive science, psychology, human-computer interaction (HCI), advertising, medical research, and other areas. A camera focuses on one or both eyes and records their movement as the viewer looks at some kind of stimulus. Most modern eye-trackers use infrared beams to create a corneal reflection , from which the angle of movement can be calculated. However eye tracking setups vary greatly; some are head-mounted, some require the head to be stable (for example, with a chin rest), and some automatically track the head as well. Most use a frequency of at least 30Hz in order to capture the detail of the very rapid eye movements.

Occular movements are typically divided into fixations and saccades, when the eye gaze pauses in a certain position, and when it moves to another position, respectively. The resulting series of fixations and saccades is called a scanpath . Most information from the eye is made available during a fixation, but not during a saccade. Furthermore, only one or two degrees of the visual angle (the fovea) is processed; higher degrees (the periphery) are generally ignored. Hence, the locations of fixations along a scanpath show what information on the stimulus was processed during an eye tracking session.

Scanpaths are useful for analyzing cognitive intent, interest, and salience. Other biological factors (some as simple as gender) may affect the scanpath as well. Eye tracking in HCI typically investigates the scanpath for usability purposes, or as a method of input in gaze-contingent displays .

References

Rayner, K. (1998) Eye movements in reading and information processing: 20 years of research. Psychological Bulletin, 124, 372-422.

Duchowski, A. T., "A Breadth-First Survey of Eye Tracking Applications", Behavior Research Methods, Instruments, & Computers (BRMIC), 34(4), November 2002, pp.455-470.