"Several theories have been proposed that shed light on the cognitive processes involved in multiple target tracking (TT). One such, described by Pylyshyn and Storm (1988) and supported by a wealth of subsequent research (e.g. Trick & Pylyshyn, 1989, 1993; Pylyshyn, 1994; Pylyshyn et al., 1994) proposes that the ability to track moving objects is dependent upon a limited number of preattentive ‘indexes’ that may be attracted to objects as they appear in the visual field and, thereafter, continue to point to them as they move, facilitating the allocation of attention to the objects’ locations."
