Abstract
Visuospatial selective attention is limited in spatial resolution (Intriligator & Cavanagh, 2001; He, Cavanagh, & Intriligator, 1996); that is, a quantifiable minimum spacing exists at which two nearby items can be isolated and selected for further processing. Previous research on attention resolution has focused on endogenous selection. Our goal was to measure the resolution of exogenous shifts of visuospatial attention. Participants viewed a circular array of equally-spaced, luminance-matched colored disks located at 10° eccentricity on a median gray background with a single RSVP stream rendered in white at fixation. Participants monitored the RSVP items for one or more target digits and responded via button press. Simultaneously, on each trial a black dot briefly (50 ms) appeared (among the peripheral colored disks) which exogenously captured attention. After each trial, participants selected via mouse-click the color (from an array of choices) corresponding to the location nearest to which the black dot had appeared on that trial. Group average results revealed that participants detected a majority of RSVP targets (51.73% hits). They also performed better than chance (~30%) at selecting the correct colored circle, and fell off approximately linearly with distance from the black cue. There was a large amount of variability between individuals, indicating that the resolution of exogenous attention is idiosyncratic. Furthermore, we found systematic differences in resolution between visual field quadrants. Nevertheless, individual participants showed strong consistency (low variability) over multiple samples at the same locations. These results suggest that the resolution of exogenous attention shifts may form a kind of attention fingerprint that describes an individual’s ability to select crowded information at various peripheral locations.