Hemispheric Differences in Higher-Order Object Processing and Effect of Expertise: Modular vs. Distributed Perspectives

What is the process by which our brains recognize higher-order visual objects, like faces, words and foreign scripts? How does perception change with experience, and what are the implications for human behavior? We are interested in exploring the extent to which face processing and word processing are mediated by different or same hemispheric mechanisms, and the extent to which experience with a particular orthographic script (English, Chinese) influences this hemispheric specialization. Two groups of participants were recruited: those who have never formally studied Chinese, and whose native language is English, and those whose native language was Chinese, and acquired English as a second language. A split-field psychophysics paradigm tests for competition and cooperation across hemispheres when participants match displays of faces or words or Chinese characters presented in the left or right visual field. Accuracy and reaction time are compared for a left versus right visual field presentation to determine hemispheric gradation for these three classes of stimuli. Whereas native English speakers show a right hemisphere advantage for faces and left hemisphere advantage for words, native Chinese speakers show a left hemispheric advantage for faces and no hemispheric advantage for words. Both groups show a left hemispheric dominance for Chinese characters. The differences and similarity between the two groups brings to light the role of experience in object representation and the potential malleability of neural resources. Results have implications for perceptual expertise, cortical plasticity, and experience-dependent perceptual learning. Hemispheric Differences 3