L1語彙の音韻処理と意味処理

概要

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Vocabulary plays a crucial role in language use, but a human mental system to process vocabulary has not been wholly clarified. In the current study, therefore, we resorted to a brain imaging technique as well as a conventional reaction time measurement to scientifically investigate how Japanese native speakers process phonology and semantics of L1 vocabulary. The subjects had three experimental tasks in a magnetic resonance imaging (MRI) scanner: a rhyme judgment task, an antonym judgment task, and a control task. By subtracting the reaction in the control task from that in each of the two lexical tasks, we identified the reaction directly concerning a phonological or semantic judgment in L1. A series of analyses of reaction time, brain activation level, and activated regions in the brain showed that semantic processing takes longer reaction time, though the brain activation levels and activated regions hardly change according to the task type; and that subjects' L1 vocabulary size and score in the reading span test influence their reaction patterns. Also, by comparing the results in the current L1 experiment and the author's previous L2 experiment, we exemplified that L1 processing takes shorter time than L2 processing, but it causes the same or the higher level of brain activation, which suggests that two different mechanisms, namely, automatization and deepening in the processing levels, concern L1 lexical processing.