Shao-Chin Hung¹, Hsiao-Lan Sharon Wang², Chien-Chung Chen¹; ¹National Taiwan University, ²National Taiwan Normal University

The classic Navon task demonstrates that humans identify global figures faster than local ones. This global precedence is challenged in dyslexics as they present a local before global perception. Here we investigated the global and local perception in 18 developmental dyslexic and 16 neurotypical Mandarin-speaking juvenile (aged 12-17 years). We employed a novel Navon task in which participants judged whether a global figure (in a global task) or local figures (in a local task) of stimuli presented on both sides of the central fixation were identical. The stimuli were large geometric shapes (i.e., circles, diamonds, or triangles) composed of smaller ones in Experiment 1. The stimuli in Experiment 2 were created similarly with three Chinese characters. In both Experiment 1 and 2, all participants showed a global precedence effect with increased accuracy in the global tasks than the local tasks. In Experiment 1, for either global or local tasks, both groups showed a congruency effect in which they responded more accurately while the local and global geometric shapes were the same than when they were different. In Experiment 2, both groups exhibited the congruency effect for the local tasks but not for the global tasks, indicating an interference from the global level to the local level, but not vice versa. Compared to the neurotypical juvenile, the dyslexics showed worse local perception possibly due to their susceptibility to visual crowding. Further, the inferior performance of dyslexics in local perception was more prominent when viewing Chinese characters than geometric shapes. In sum, we found no evidence for the local precedence either for geometric shapes or Chinese characters in dyslexia. The impaired local perception of Chinese characters observed in dyslexics may suggest specialized channels for visual word form processing.

Acknowledgements: NSTC 113-2410-H-002-251-MY3