Holistic but with reduced right-hemisphere involvement: The case of dyslexia in Chinese character recognition

Recent research on visual object recognition has suggested that the right hemisphere can engage either holistic or part-based processing depending on whether the recognition relies on configural (exact distances among features) or featural information, respectively. Consistent with this finding, expert Chinese reading has been marked by a left-side bias (an indication of right-hemisphere lateralization) with decreased holistic processing (as assessed using the composite paradigm) due to its reliance on featural information. Here we examine two common perceptual expertise phenomena in object recognition - holistic processing and left-side bias - of Chinese characters in adolescents with developmental dyslexia and matched controls. We found that those with dyslexia showed stronger holistic processing, a weaker left-side bias, and worse performance in Chinese character dictation than controls. This was in contrast to Limited writers (proficient readers with limited writing experience) reported in Tso, Au, and Hsiao (Psychological Science, 25, 1757-1767, 2014), who showed stronger holistic processing and worse dictation performance, but the same level of left-side bias as controls. This result demonstrated two different perceptual mechanisms underlying holistic processing: Limited writers' holistic processing may be due to difficulties in de-emphasizing configural information unimportant to Chinese characters, whereas readers with dyslexia may have deficits selectively attending to character components to form appropriate part-based representations in the right hemisphere.