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.

Chinese character recognition is based on a limited set of recurrent stroke patterns. Most Chinese characters are a combination of two or more of these components. To test whether readers are sensitive to combinations of components (or multi-component units [MCUs]) within a character, we conducted two probe detection tasks where participants had to detect the presence of a component in a target character. Critically, some targets contained an MCU that can stand as a character on its own, with its own meaning and sound, while other targets contained an MCU that only exists embedded within other characters (no associated meaning and sound). Participants had more difficulty detecting component probes that were a part of an existing MCU, compared to component probes that belonged to a non-existing MCU. These findings suggest that existing MCUs are a perceptual unit in Chinese character recognition.