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Poster A37, Thursday, August 16, 10:15 am – 12:00 pm, Room 2000AB

Lexical access and integration in context: a fixation-related fMRI study of the word predictability and word frequency interaction during sentence comprehension

Jie-Li Tsai1, Guan-Huei Lee1, Chia-Ying Lee2, Chung-I Erica Su1, Tzu-Hsuan Lin1;1National Chengchi University, Taiwan, 2Academia Sinica, Taipei, Taiwan

The present study aims to examine the neural correlates of the contextual predictability and frequency effects in the natural reading of Chinese sentences. Processing a word in sentence involves lexical access of word representation and semantic integration with the prior context. Lau, Phillips, and Poeppel (2008) proposed an cortical network of semantic processing in sentence comprehension, including the left posterior and anterior temporal cortex, and the left inferior frontal cortex. With simultaneous eye movement recording, a fixation-related fMRI experiment was conducted to investigate the brain responses contingent to the fixation events on reading words in sentences. Forty participants read one hundred sentences, in which a target word was embedded in the middle to the third-quarter location of each sentence. Half of the targets were low frequency (LF) words and the second half were high frequency (HF) words. The targets were either with low predictability (LP) or high predictability (HP) according to the prior context of the leading sentence fragment. The functional T2-weighted images were acquired (TR = 2s) and the fixation onset of the first-pass gaze on the target was used as the fixation-related event for modeling the hemodynamic brain response. For word frequency, the results showed that low frequency words involved more activations in the left IFG and left insula than high frequency words did. For word predictability, low predictable target words demanded higher activation in the left inferior frontal gyrus (IFG) and left middle temporal gyrus (MTG) than the predictable target words did. These findings suggest that these regions are responsible for the semantic integration of the lexical representation of a word and its prior context. Critically, high and low frequency words revealed different patterns of the predictability effect in the brain. For low frequency words, the left IFG had higher activation for low predictable targets than that of high predictable targets. In contrast, the predictability effect of high frequency words was mainly showed in the anterior and posterior MTG. The findings are consistent with the previous fMRI studies of semantic processing, and further imply the role of the left IFG for controlled retrieval of word semantic and the MTG for automatic access of word representation.

Topic Area: Meaning: Lexical Semantics