| Summary: | 碩士 === 國立臺灣大學 === 語言學研究所 === 107 === Prior studies have found reliable structural-based syntactic processing (indexed by the P600 responses) in the left hemispheres (LH) in young right-handers without familial sinistrality (FS-) but bilaterally in FS+ young adults, leading to the hypothesis that the right hemisphere (RH) is capable of structural analysis. RH P600 responses are usually masked via inter-hemispheric suppression; however, little is known about factors modulating such suppression and whether the RH of left-lateralized individuals can still acquire P600 responses.
To unravel the puzzles, 32 young right-handed FS- Chinese speakers underwent two Event-Related Potential (ERP) sessions and two behavioral experiments. In ERP session one, participants viewed and judged the grammaticality of Chinese phrases containing a centrally-presented one-word syntactic cue (adverb/classifier) followed by a laterally-presented verb or noun, matching or mismatching the syntactic expectancy. In ERP session two, the participants learned a monaurally presented artificial language (AL) and judged the grammaticality of another set of strings after training. In the behavioral session, participants’ abilities of inter-hemispheric inhibition and coordination were examined. In the first behavioral experiment (bilateral flanker task), participants attended to and judged the direction of a horizontal arrow presented in a pre-specified visual field (VF), with another arrow or a square appeared simultaneously in the non-attended VF to form congruent/incongruent or neutral conditions. Last but not least, in the Word-matching task, participants were asked to judge the semantic relatedness of two Chinese characters that either in unilateral or in bilateral presentation.
The results from native language processing showed a reliable P600 grammaticality effect only in the LH, replicating prior research. Further analysis supported the link between left-lateralized P600 and inter-hemispheric inhibition by revealing a correlation between the magnitude of RH P600 responses and LH-on-RH inhibition, with smaller RH P600 associated with more effective inhibition. Interestingly, data from AL processing showed bilateral P600 grammaticality effects. A mean-split based on the accuracy of grammaticality judgment in the AL session showed that P600 effects were lateralized to the LH in high performers but bilaterally present in low performers while both groups showed a left-lateralized P600 effect during native grammar processing. Last but not least, the correlational results also revealed that the leftward lateralization of AL syntactic processing was associated with better ability of the inter-hemispheric coordination. Together, these findings suggest that language lateralization may be jointly determined by multiple modulating factors, including inter-hemispheric interactions and language proficiency.
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