The effect of attentional spread on spatial resolution.

The effects of attentional spread were studied by having subjects detect a luminance increment along a row of evenly spaced dots. The increment could occur for the central, fixated dot (Narrow Attention) or for either the fixation dot or one of the four dots to its left or right (Broad Attention). Narrow Attention enhanced the detection of luminance increments for the fixated dot, and also enhanced spatial resolution near the fixation dot for judgments of vernier alignment and separation. This indicated that the sensitivity of small spatial filters in the fovea was increased more by narrowly focused than broadly spread attention. Effects of attentional spread on spatial resolution were not obtained for judgments of the separation between two peripherally located targets, perhaps because of their dependence on eccentricity (position) rather than separation.