On-Ting Lo joined the department of Psychology at the University of Hong Kong in 2010 where he currently is in his final year for his PhD. His primary research interest is: Visual processing of Chinese character recognition.
Flanker contrast explains the effects of flanker complexity on crowding in Chinese character recognition.
On-Ting LO, Sing-Hang CHEUNG Department of Psychology, The University of Hong Kong
Objective: Crowding is stronger when Chinese target and flankers are in a same complexity level than in mixed ones, consistent with a grouping by complexity hypothesis (Zhang et al, 2009 Vision Research 49 44 53).
Crowding strength also increases with flanker contrast level (Chung et al, 2001 Vision Research 41 1833 1850).Here we study the effect of scaling the flanker contrast on crowding with flankers of similar or different complexity. Method: Stimuli (size=1°) were 100 Chinese characters (CC) of two complexity levels. Five observers were tested binocularly at 7° eccentricity in their right visual field. Center to center distance in the flanked conditions was 2°. Contrast threshold for recognizing single or flanked CC (67.6% accuracy) was measured by QUEST. Threshold elevations (TE) in recognizing a simple CC in two flanker complexity conditions (simple vs. complex) were measured. In Experiment 1, flanker contrast was always 3x the contrast threshold of recognizing a single complex CC. In Experiment 2, the flanker contrast was 2.5x the contrast threshold of recognizing a single simple or complex CC in the corresponding flanker complexity condition.
Results: Simple flanker resulted in stronger crowding (log TE = 76±.09) than complex flanker did (log TE = .33±.11) in Experiment 1. When we scaled the flanker contrast according to the contrast threshold of the two complexity levels, simple (log TE = .43±.08) and complex (log TE = .41±.12) resulted in similar crowding strengths in Experiment 2.
Conclusions: Crowding is stronger when target and flankers have a same complexity level when flanker contrast is the same between the complexity conditions. However, weaker crowding from flankers of different(and higher) complexity can be explained by the higher contrast threshold required to process such flanking characters. Our findings suggest that the flanker complexity effect is not due to the similarity rule in crowding.
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