Eye tracking software.

Eye-tracking

What is eye-tracking?

Eye-tracking aims to determine where one directs one’s gaze, or, put simply, it where one looks (for instance, on a computer monitor). Because of the richness and importance of visual information in the environment and because the acuity (sharpness) of human vision rapidly falls off as one departs from the centre of the gaze’s focus, humans have evolved to possess a powerful (fast and effective) oculomotor system: six muscles that move the eye-ball in the eye-socket guided by groups of cells in several regions of the brain, most notably in the superior colliculus and frontal eye fields. The behaviour of the oculomotor system is characterised by two states: the gaze is either (virtually) stationary- referred to as ‘fixation’- or it is on a fast move- referred to as ‘saccade’. Since research to date has convincingly shown that no information is acquired during the eye-movement (saccade), which means we only see during the fixation, psychologists tend to be interested in the latter: the location and duration of fixations.

Researchers interested in perception, attention, reading, face processing, scene perception and other areas of cognitive psychology, use the temporal and spatial distribution of fixations to make inferences about ways in which visual information is selected and processed. Neuroscientists interested in the control of eye-movements are often more interested in saccades than in fixations- their timing, velocity, trajectory and targeting. Technologically, eye-tracking relies on ‘beaming’ infra-red light towards the eye and measuring the reflected light from the retina (the back of the eye). Because this reflection depends on the angle between the eye and the measuring camera, one can track the position of the eye (and therefore the gaze) very precisely.

How do we use eye-tracking?

Because eye-movements are fairly tightly coupled to selective visuo-spatial attention, our primary use of eye-tracking is as a measure of spatial attention. We are also starting to use eye-movements to examine language processing and preferences and sampling in decision making tasks. Recently, we have fruitfully combined eye-tracking with concurrent recordings of event-related potentials.

Is eye-tracking safe?

Eye-tracking is perfectly safe. The levels of infrared radiation directed at the eye are very small indeed, smaller than the ones that would reach the eye when one looks at, say, a hot oven from some distance. There is also no associated sensation because infrared light is invisible to the human eye.

More information on eye-tracking research: www.scholarpedia.org/article/Eye_movement.