Abstract
Purpose :
Previous studies disagree as to whether visual performance is impaired more by flanking stimuli that have the same (congruent) vs. a different (incongruent) color as the target to be identified. In this study, we compared the effect of color congruent and incongruent flankers and targets on the magnitude and extent of crowding (CW) and contour-interaction (CI) in foveal and peripheral vision.
Methods :
Single Sloan letters were presented at the fovea or at 5 deg in the inferior visual field, with and without flanking bars or letters placed symmetrically to the right, left, top and bottom. Flanking bars or letters were either color congruent (red-red or green-green) or incongruent (red-green or green-red) with respect to the target letter. All targets and flankers had approximately equal Weber color contrast (-79%). At each eccentricity, the target size was chosen so that each subject (n=4) could identify the letters with ~80% accuracy in the absence of flankers. Edge-to-edge flanker-to-target distance varied from 10 – 200% of the letter size. The magnitude and extent of foveal and peripheral CW and CI were defined from plots of percent correct letter identification vs. target-to-flanker distance, separately for color congruent and incongruent stimuli.
Results :
Plots of foveal CW and CI were similar and showed no difference between the color congruent and incongruent conditions. At an eccentricity of 5 deg, both the magnitude and extent of CW were greater than CI, as reported previously. As in the fovea, no differences in CW or CI were found at 5 deg for color congruent vs. incongruent stimuli.
Conclusions :
The results suggest that grouping by color does not significantly influence the mechanisms that mediate CW or CI. The data also indicate that CW and CI depend on different underlying mechanisms in the fovea and periphery and that the most relevant input to these mechanisms is luminance rather than chromatic contrast.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.