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Poster C9, Thursday, November 9, 10:00 – 11:15 am, Harborview and Loch Raven Ballrooms

Left-lateralized syntactic category processing is modulated by interhemispheric inhibition in healthy young right-handers with familial sinistrality background

Yi-Lun Weng1, Min-Hsin Chen1, Chia-Lin Lee1;1National Taiwan University, Taiwan

Left-hemisphere (LH) specialization for syntax is often viewed as a key example of functional lateralization, however, recent studies have demonstrated that the right hemisphere (RH) is capable of initiating processes similar in nature. To better understand factors modulating this functional lateralization, we examined the hypothesis that LH-equivalent language capabilities in the RH are masked by transcallosal interhemispheric inhibition from the dominant LH. In particular, we focused on a participant population previously found with reduced language lateralization—healthy young right-handers with a history of familial sinistrality (FS+). Event-related potentials (ERPs) were recorded from 25 participants while they judged grammaticality of Chinese two-word phrases. Following a central syntactic cue predictive of either a noun or a verb, target words were laterally presented to either visual field (VF), matching or mismatching the syntactic category expectancy (e.g., Grammatical: liǎng-dòng fáng-zi “two houses”; jí-shí bang-máng “to immediately help”. Ungrammatical: jí-shí fáng-zi “immediately house”; liǎng-dòng bang-máng “to two help”). Target-locked ERPs revealed a reliable P600 grammaticality effect (600-1100 ms) with both VF presentations, replicating reduced syntactic lateralization in FS+ individuals previously found in studies based on English. In the same participants, we assessed their transcallosal interhemispheric inhibition using a bilateral flanker task, in which participants judged the direction of an arrow in the attended VF while ignoring distracting information from the other VF. Reaction times between the incongruent and neutral distractors were calculated for attend-RVF and attend-LVF conditions separately to index processing costs for inhibiting distracting information from the RH and LH respectively. Sizes of the P600 responses with each VF presentation were then regressed against the inhibition indices derived from the flanker task. Results showed that larger LVF/RH P600 responses were associated with less effective LH-on-RH inhibition (indicated by larger attend-RVF congruency effect)(r = 0.46, p <.05). However, no systematic relation was found between the RVF/LH P600 responses and the RH-on-LH inhibition cost (indicated by the attend-LVF congruency effect) (p = .71). These results thus support the hypothesis that callosal inhibition, especially the inhibition from the dominant LH on the RH, modulates the lateralization pattern of structural analysis in syntactic category processing reflected by P600s, rendering the more bilateral responses in FS+ young adults a consequence of reduced interhemispheric inhibition.

Topic Area: Grammar: Syntax

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