Poster D68, Wednesday, August 21, 2019, 5:15 – 7:00 pm, Restaurant Hall
Effects of structural complexity on sentence comprehension: An fMRI study of late second language learners
Kaoru Koyanagi1, Hyeonjeong Jeong2, Fuyuki Mine1, Yoko Mukoyama3, Hiroshi Ishinabe2,4, Haining Cui2, Kiyo Okamoto2, Ryuta Kawashima2, Motoaki Sugiura2;1Sophia University, 2Tohoku University, 3Musashino University, 4Higashiosaka Junior College
Previous neuroimaging studies on first languages (L1) have demonstrated that processing complex sentences (e.g., scrambled word order; O-S-V) enhances heavier cognitive demands for linking syntactic and semantic information than processing their canonical (S-O-V) counterparts (Kim et al., 2009; Makuuchi & Friederici, 2013). These kinds of cognitive demands are processed in the core language systems, such as the left inferior frontal gyrus (LIFG) and the posterior temporal areas. However, this may not be true for L2 processing, as it requires additional cognitive resources due to various factors, such as the age of acquisition and L2 proficiency levels. The current fMRI study first attempted to investigate the effect of structural complexity (i.e., scrambled sentences vs. canonical sentences) on the brain during L2 sentence comprehension by comparing L1 comprehension. Then, the study attempted to identify the effect of L2 proficiency levels on the brain mechanism. Participants were 33 healthy right-handed Chinese and 20 Japanese native speakers, respectively. The Chinese speakers learned Japanese as L2 (mean age 24.21, 20 females). Participants’ L2 proficiency level was tested with Tsukuba Test-Battery of Japanese. The Japanese speakers were undergraduate and graduate students at a university (mean age 21.95, 10 females). They were asked to perform a semantic-plausibility judgment task with auditory-presented Japanese sentences during fMRI scanning. A total of 168 Japanese sentences were created along with 56 semantically implausible sentences as a filler condition. After dividing two sets of sentences for canonical and scrambled words order, we counterbalanced these sentences among participants. We modeled four regressors of Canonical, Scramble, Filler, and Error (incorrect responses) in each participant. For second-level analyses, we tested 2 (Group: L2 and L1) x 2 (sentence complexity: Canonical and Scramble) factors and interaction with the flexible two-way ANOVA implemented in SPM12 (corrected to p<0.05 by cluster size). Furthermore, to examine the effects of L2 proficiency levels on the brain during complex sentence comprehension, correlation analysis was conducted in the contrast [Scramble>Canonical] for the L2 group with the proficiency scores of each participant at the whole brain level. First, as a main effect of the group, higher activation was observed in the left middle frontal gyrus and left caudate for the L2 than L1 groups, but the semantics areas such as the left middle temporal gyrus (LMTG) and ventral part of IFG were involved much more heavily for the L1 than L2 groups. Second, the main effect of complexity [Scramble > Canonical] was observed in the left middle frontal gyrus (LMFG), LIFG, and supplementary motor area. Third, there was no significant interaction effect between group and complexity. However, significant positive correlation between activation in L2 [Scramble>Canonical] and proficiency levels was found in the LMFG, left hippocampus, and LMTG (p<0.001, uncorrected). Taken together, these findings suggest L2 learners rely on heavier cognitive control and working memory demands during L2 sentence comprehension than L1 speakers do. As L2 proficiency increases, L2 learners may efficiently integrate working memory and semantics areas in order to comprehend meanings of sentences with complex structures.
Themes: Perception: Auditory, Development
Method: Functional Imaging