Ocular Measures of Fatigue
and Cognitive Factors
Erik J. Sirevaag John A. Stern Washington University
The gaze control system consists of the mechanisms concerned with the acquisition of visually presented information. Elements of this system include the eyes and associated musculature, the pupils, the eyelids, head and neck muscles, and the neural structures responsible for coordinating the complex task of producing a focused image of a potential information source upon the fovea. By virtue of the control exerted over the flow of visual input, this system is an excellent reflector of aspects of information processing. However, the sensitivity of the system to information processing is not restricted to the selective acquisition of visual information. Auditory information, as well as task difficulty and complexity, can also influence the control of gaze. We first review the literature dealing with issues of fatigue and information processing as they impact on and are reflected in the gaze control system, and we conclude with a discussion of issues that must be considered when attempting to implement measures of oculomotor activity in applied settings.
What can these systems tell us about cognitive processes in general, and "mental fatigue," an admittedly vague concept, in particular? Everyone knows when they feel fatigued, but an objective measure of this construct has yet to be developed. We will assume that work-induced fatigue develops as a function of time-on-task, and that the rate at which fatigue effects appear is a function of the complex interaction between a variety of both subject and task variables.
Subject variables include state factors (i.e., sleep history, drug intake, and biological rhythms) and trait attributes (i.e., the ability to focus and maintain attention). Task variables include the nature (perceptual/central/motor) as well