I have been thinking about eye-tracking for a while, especially after the interview for a PhD that I am applying to. Indeed eye-tracking, dilletary pupil may not be a direct indication of cognitive load. Well, even to begin with cognitive load is not well understood yet. It is consisted of many activities that is difficult to separate and identified (for now at least. or maybe I am just lacking in my paper research about the relation between eye tracking and cognitive activity).
I am actually interested to know does eye-tracking measure attention?
Meanwhile, it turns that I am not the only one who would like to know if there is any scientific experiment that relate eye-tracking with cognitive load.
Dilation of the pupil is caused by neurons of the Sympathetic Nervous System innervating radial fibres of the iris, whereas its constriction is by means of Parasympathetic Nervous System neurons innervating the circular fibres. Thus, pupil dilation can be used to measure cognitive load, as well as emotional and other psychological responses. Some classic references for the use of pupil diameter to examine cognitive load are Beatty, 1982; Goldwater, 1972; Hyönä, Tommola, & Alaja, 1995, and Kahneman, 1973.
However, one of the main problems in physiological measure in general is the constant fluctuations in activity that are irrelevant to the manipulation (e.g., pupil diameter fluctuations which occur constantly during waking hours). These background variations in autonomic activity are associated with a variety of factors that cannot be easily interpreted. In addition, since pupil diameter serves as an index of general physiological arousal, the specific determinants that give rise to the arousal cannot be easily inferred.
To address these issues, one should use repeated trials, and analyze event-related arousal. As habituation might also be a problem, the repeated trials of each type of event should be randomized. Finally, establishing a good baseline measure of arousal, and comparing it to arousal after the manipulation could also help make a stronger connection between arousal and cognitive load.
Because for me, indeed eye-tracking device has been widely used in usability research. But what is actually being measured and what does the measurement means? I think is a fundamental question before I use eye-tracking device as a measurement device.
How Does an Eye Tracker Work?
Most commercial eye-tracking systems available today measure point-of-regard by the “corneal-reflection/pupil-centre” method (Goldberg & Wichansky, 2003). These kinds of trackers usually consist of a standard desktop computer with an infrared camera mounted beneath (or next to) a display monitor, with image processing software to locate and identify the features of the eye used for tracking. In operation, infrared light from an LED embedded in the infrared camera is first directed into the eye to create strong reflections in target eye features to make them easier to track (infrared light is used to avoid dazzling the user with visible light). The light enters the retina and a large proportion of it is reflected back, making the pupil appear as a bright, well defined disc (known as the “bright pupil” effect). The corneal reflection (or first Purkinje image) is also generated by the infrared light, appearing as a small, but sharp, glint.
Read these papers:
Noted that I am not an expert in eye-tracking usage, any comments or thoughts would be appreciated.