Edward K. Vogel

University of Oregon

Attention can be divided so that multiple objects can be tracked simultaneously as they move
among distractors. Although attentional tracking is known to be highly limited, such that most
individuals can track only approximately four objects simultaneously, the neurophysiological
mechanisms that underlie this capacity limitation have not been established.

Here, we provide electrophysiological measures in humans of the initial selection and
sustained attention processes that facilitate attentional tracking. Each measure was modulated
by the number of objects the subject was tracking and was highly sensitive to each individual's
specific tracking capacity. Furthermore, this activity was highly sensitive to dynamic changes in
the subject's tracking load during the trial. Consequently, these measures provide an online
measure of the object representations that are currently being tracked and help to link these
attentional capacity limits to other cognitive capacity limitations.