Poster E37, Thursday, August 22, 2019, 3:45 – 5:30 pm, Restaurant Hall
Disentangling morphological decomposition and letter recognition: An MEG study of Japanese verbs
Shinri Ohta1,2, Yohei Oseki2,3, Alec Marantz2,4,5;1Department of Linguistics, Kyushu University, 2Department of Linguistics, New York University, 3Faculty of Science and Engineering, Waseda University, 4Department of Psychology, New York University, 5NYUAD Institute, New York University Abu Dhabi
Previous magnetoencephalography (MEG) studies reported that morphologically complex words are decomposed into morphemes around 170 ms after the onset of visual stimuli (M170) in the left fusiform gyrus and inferior temporal gyrus (FG/ITG). Moreover, another MEG study found that transition probability between morphemes (morphTP) was negatively correlated with the amplitude of the M170. As these studies targeted English, in which morphological boundaries are a subset of letter boundaries, it is difficult to examine whether the M170 is modulated by morphTP or TP between letters (letterTP). To disentangle morphological decomposition and letter recognition, we targeted the Japanese language, which uses logographic kanji and moraic kana writing system. For example, in Japanese verbs, kanji and kana represent the verbal root and remaining morphemes, respectively, leading to a mismatch between morpheme boundaries and letter boundaries. In the present MEG experiment, we compared the effects of morphTP (TP between verbal root and suffixes) and letterTP (TP between kanji and kana) on the left FG/ITG activation. We recruited 22 right-handed native speakers of Japanese (nine males, 35.5±7.3 yrs.). We used 112 Japanese verbs for each of intransitive verbs, transitive verbs, intransitive-causative verbs, and transitive-causative verbs, as well as the same number of nonwords (total 896 stimuli). The participants performed a visual lexical decision task. We used a 157-channel MEG system (Kanazawa Institute of Technology). For the MEG analyses, we used spatiotemporal cluster permutation tests as implemented in MEG-Python and Eelbrain packages. As our primary target was the M170, the region of interest was anatomically defined as the left FG/ITG and the analysis time window was restricted to 50-250 ms after word onset. A two-way repeated-measures analysis of variance (transitivity*causativeness) for the accuracies showed significant main effects of transitivity and causativeness, as well as an interaction (transitivity: p=0.046, causativeness: p<0.0001, interaction: p=0.042). The reaction times also showed a significant effect of causativeness, but neither a main effect of transitivity nor an interaction was significant (transitivity: p=0.39, causativeness: p<0.0001, interaction: p=0.34), indicating that the causative conditions were more demanding. For the MEG data, we first examined whether transitivity and causativeness modulated activation in the left FG/ITG. We found a significantly larger activation in the noncausative conditions in the anterior part of the left FG/ITG (corrected p=0.044), but the main effect of transitivity was not significant (corrected p>0.2). Because the TP from the verbal root to the causative suffix was lower than that of the verbal root to a tense suffix, this activation may reflect the difference of the morphTP. We further examined whether the morphTP modulated the left FG/ITG activation, by using spatiotemporal cluster regression analyses. We found a significant negative correlation between the morphTP and the left FG/ITG activation (corrected p<0.03). In contrast, we did not find any significant correlation between the letterTP and the left FG/ITG activation (corrected p>0.2). These results demonstrated that morphologically complex verbs in Japanese are indeed decomposed into morphemes, but not into letters, similar to morphologically complex words in English examined in the previous MEG studies.
Themes: Morphology, Writing and Spelling
Method: Electrophysiology (MEG/EEG/ECOG)