Crowding Affects Letters and Symbols Differently

Five experiments examined crowding effects with letter and symbol stimuli. Experiments 1 through 3 compared 2-alternative forced-choice (2AFC) identification accuracy for isolated targets presented left and right of fixation with targets flanked either by 2 other items of the same category or a single item situated to the right or left of targets. Interference from flankers (crowding) was significantly stronger for symbols than letters. Single flankers generated performance similar to the isolated targets when the stimuli were letters but closer to the 2-flanker condition when the stimuli were symbols. Experiment 4 confirmed this pattern using a partial-report bar probe procedure. Experiment 5 showed that another measure of crowding, critical spacing, was greater for symbols than for letters. The results support the hypothesis that letter-string processing involves a specialized system developed to limit the spatial extent of crowding for letters in words.