Abstract
Shifts of visuospatial selective attention are limited in spatial resolution (i.e., the required spacing surrounding a target for successful selection; Intriligator & Cavanagh, 2001). Previous research on attention resolution has focused on endogenous selection, but exogenous resolution has been unexplored. We measured and compared the resolution of exogenous shifts of visuospatial attention at two different eccentricities by quantifying the minimum spacing needed for individuals to isolate and select a peripheral target among nearby distractors. Concurrently, we evaluated if exogenous selection operates at a finer resolution than endogenous selection. Participants viewed a circular array of equally spaced, luminance-matched colored disks at 10° (Experiment 1) or 7.5° eccentricity (Experiment 2) on a median gray background with a single white RSVP stream at fixation. The size of the peripheral-colored disks was scaled with eccentricity to conserve inter-disk spacing (diameters were 0.75° and 0.56°, respectively). Subjects monitored RSVP items for target digits and responded via button press. Simultaneously, on each trial a black dot briefly (60 msec) appeared (among the peripheral-colored disks) which exogenously captured attention. After each trial, participants selected the color corresponding to the location nearest to which the black dot had appeared. Responses were compared to an ideal observer model to determine the attentional window size each subject deployed in response to the exogenous cue, which was then used to quantify the minimum stimulus spacing required for 75% accuracy. Preliminary data suggests that color selection task accuracy was nearly equivalent in Experiments 1 (M = 49.5%) and 2 (M = 50.1%). However, minimum calculated spacing estimates were smaller at the decreased eccentricity (Expt. 1 = 1.051°; Expt. 2 = 0.988°). Nevertheless, both of these minimum spacing estimates are smaller than published data on endogenous attention. Thus, exogenous selection operates at a finer resolution than endogenous selection at the same eccentricities.