The concept of attention is most intriguing since, at first glance, it appears impossible to study. Somehow it seems more feasible to examine and determine the basic structure of perceptual or mnemonic processes – establishing parameters such as perceptual thresholds and memory capacities. It is unsettling to learn that a slight attentional change, for example in the instructions of a task, can radically change these so-called parameters of the system. That is, telling a subject where a target is likely to appear, or what target is likely to appear, might determine whether or not the subject will be able to detect, discriminate, or even remember the target.

The relation between attention and eye movements

The relation between eye movements and attention has been discussed for over a century, but usually in the context of dissociating attention from eye movements. In 1890, William James in The Principles of Psychology noted that “we may attend to an object on the periphery of the visual field and yet not accommodate the eye for it” (p. 413). He further elaborated by referring to Helmholtz, who, according to James, “states the fact so strikingly that I will quote his observations in full” (p. 414).