Abstract
Most crowding studies are performed at the periphery, and some showed that tagging can reduce crowding. We have shown that crowding also occurs at the fovea for short stimulus duration and that target’s color tagging abolished foveal crowding but not in a short presentation time (40 ms). Several studies show that color recognition is also impaired under crowding at the periphery. Therefore, we asked whether the mechanisms of letter-identification and black/red discrimination under foveal crowding and short presentation time are distinct? Fifteen adults with normal or corrected-to-normal vision participated in the study. E target (black or red, with the same luminance) was briefly presented (20, 40, 120 ms) at the fovea, either in isolation (single condition) or surrounded by a 0.4 letter-spacing matrix of randomly rotated E letters (black/red, single/crowding), creating the same or distinct color of the target (pop-out). The task was to identify the direction of the E target (right/left) and to discriminate between the colors (black/red), reporting either the direction first and then color, or in reverse order for control; Effects of matrix contrast and backward masking method at different time intervals were also tested. Crowding is remarkable for the short presentation time but is significantly decreased with increasing presentation time. The black/red discrimination decreased significantly (p=0.0002 for black and p<0.0001 for red) relative to a single letter in short presentation times (20, 40 ms) and returned almost to the single letter level for the longer time (120 ms). Reducing matrix contrast reduced crowding and improved the black/red discrimination. Our results are consistent with the notion that crowding produces a high processing load and a bottleneck on visual processing. Pop-out abolished the crowding but became almost ineffective for short presentation time suggesting that discrimination of black/red is slower than monochromatic processing of letter-identification.