Novel Color Stimuli for Studying Spatial Attention

Abstract

The effects of covert spatial attention on color processing are not well known. Although feature-based attention to color is known to improve discrimination performance, no studies (we know of) have examined the effects of spatial cueing on color processing. Here, we report results using a novel color stimulus that incorporates many of the desirable features found in visual motion stimuli commonly used in spatial attention tasks. The stimuli were circular patches (3.23° radius) comprised of ~660 squares, each with a color randomly drawn from a Gaussian distribution along one axis of DKL space, plus a randomly chosen luminance increment or decrement. Similar to dot-motion stimuli, each square was reborn after a fixed "lifetime" with a new color and luminance. By varying the mean and standard deviation of the Gaussian distribution, we defined stimuli that differed from one another in discriminability. We used these stimuli in a spatial attention task. In the main experiment, human subjects were shown 4 patches (1 in each quadrant at 8° eccentricity) while maintaining central fixation, and the mean color in one of the patches changed during the trial. The task was to report the "direction" of the color change (2AFC). In 50% of trials (cued block), a pre-stimulus cue indicated (100% valid) the location of the impending change; otherwise, the change could occur at any of the 4 patches (uncued block). In a control experiment, subjects performed the same 2AFC task with a single patch. Results from 3 subjects show that thresholds in the cued block were significantly lower than those in the uncued block, and nearly identical to those in the single-patch control. These results demonstrate that spatial cues can selectively enhance the processing of color stimuli, and illustrate the usefulness of these novel stimuli for studying spatial attention to color. Meeting abstract presented at VSS 2013