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Lei Liu, Jun-Yun Zhang, Cong Yu; Internal and external crowding in recognition of Chinese characters. Journal of Vision 2007;7(9):593. doi: 10.1167/7.9.593.
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© ARVO (1962-2015); The Authors (2016-present)
Crowding refers to the deteriorated target identification in the presence of nearby flankers. We studied crowding in recognition of Chinese characters (CCs) in normal and anisometropic amblyopic observers. The stimuli were four groups of CCs with various spatial complexities and English Sloan letters presented at 0o, 5o, and 10o retinal eccentricities. (1) Under no-flanker conditions, acuity sizes of more complex CCs increased faster with retinal eccentricity than that of simpler CCs and Sloan letters, suggesting possible internal crowding among components of complex CCs in peripheral vision. (2) When the target was flanked by same-sized characters from the same stimulus group at a 1-character size gap, strong external crowding was evident in peripheral vision, but internal crowding for complex CCs was not carried over to external crowding. (3) Crowding was reduced by 30–45% when the spatial complexities of the flankers and the target were different. More complex flankers reduced more crowding to a simpler target than did simpler flankers to a more complex target. (4) Acuity sizes for all stimuli were larger in anisometropic amblyopic eyes than in non-amblyopic and normal eyes up to 10o retinal eccentricity. However, internal crowding of more complex CCs observed in normal eyes was not shown in amblyopic eyes. External crowding that prevailed in normal and non-amblyopic eyes was very weak in amblyopic eyes. Our results indicated that both internal and external crowding affected the recognition of CCs in the visual periphery, which should be considered when Chinese reading using peripheral vision is evaluated. Both low level lateral masking and high level attention deployment may be responsible for the observed crowding reduction when target and flankers had different spatial complexities. Unlike normal or non-amblyopic eyes, anisometropic amblyopic eyes seemed to be immune to crowding across the visual field.
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