| Summary: | 碩士 === 輔仁大學 === 跨文化研究所語言學碩士班 === 107 === In his seminal critical period hypothesis, Lenneberg proposed that both left and right hemispheres of the brain are involved during children’s language abilities development. In line with this theory, some findings have suggested that the shift from bilateral brain activity pattern to left-hemisphere dominance pattern occurs gradually with age, from childhood to adolescence. This shift has been thought to reflect the progression of brain maturation. However, little is known about how brain responses in the right hemisphere (RH) during the lateralization process are related to children’s language ability. To take a first step towards understanding the nature and consequences of leftward lateralization in children, the present study utilized the event-related potential (ERP) and divided visual field paradigm (DVF) techniques to investigate children’s brain responses to syntactic information, with particular foci on the nature of RH activity and the relation between the degree of lateralization and reading proficiency.
We targeted children aged 8 to 10 as during this age range, reading comprehension performance varies widely even though basic vocabulary and syntactic knowledge are already in place. Twenty-six right-handed children were tested, all of whom were native speakers of Taiwan Mandarin. All participants completed two experiments. Experiment 1 attempted to investigate brain responses to word class violation. Participants read two-word phrases at the center of the screen. The results showed an N400 grammaticality effect (300-850 ms) was followed by a P600 grammaticality effect (850-1400 ms). In experiment 2, participants viewed and judged the grammaticality of 216 two-word Chinese phrases. Each phrase contained a centrally presented one-word syntactic cue (adverb/classifier) followed by a laterally presented verb or noun, matching or mismatching the syntactic expectancy. Subsequent to the ERP recording session, information regarding participants’ language abilities was collected off-line using a paper-and-pencil reading comprehension test designed to evaluate sentence-level, inferential-level, and integrate-level comprehension. ERP results were measured for both N400 (mean amplitudes between 350-750ms) and P600 (differences between negative peaks measured during 350-750ms and positive peaks measured between 750-1400ms) responses. Correct trials from all participants as a group revealed both N400 and P600 grammaticality effects, both symmetrically shown in the right visual field (LH-biased) and left visual field (RH-biased) conditions. To examine the relation between brain responses and language ability, further analyses were done based on a median split of their on-line grammaticality judgment performance. These two subgroups were comparable in age and numbers of males and females, but the higher-score group performed reliably better in the offline comprehension test than did the lower-score group. The subgroup results showed, for the higher-score group, left-lateralized N400 and P600 effects. For the lower-score group, however, bilateral N400 and P600 effects were observed.
The results of this study are consistent with bilateral brain activations in children of this age previously reported in brain imaging studies. Furthermore, these results provided further information indicating that both hemispheres engage qualitatively similar processes. We noted individual variations in the degree of lateralization among children. In particular, bilateral processing has a tendency to associate with lower behavioral accuracy. Interestingly, the bilateral pattern in lower behavioral has a tendency with more FS+ background. These findings corroborated the view that degrees of language lateralization are variable and are consistent with prior findings from adults linking bilateral- or RH- P600s with more challenging language processing. Overall, these results also suggest a transition from bilateral to more lateralized language processing from children with poorer reading ability to better reading ability.
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