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Neurobiological bases of morphological decomposition and recomposition in Tagalog: MEG evidence from inflectional morphology
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Poster E30 in Poster Session E, Thursday, October 26, 10:15 am - 12:00 pm CEST, Espace Vieux-Port
Dave Kenneth Cayado1, Samantha Wray2, Marco Chia-Ho Lai3, Linnaea Stockall1; 1Queen Mary University of London, 2Dartmouth College, 3New York University
Morphological decomposition and recomposition stages were recently investigated in English (Stockall et al., 2019) and Greek (Neophytou et al., 2018), with evidence emerging for three distinct processing stages: [1] a decomposition stage, where morphologically complex words are segmented into morphological units in the left visual word form area (VWFA) between 100-200ms; [2] a syntactic category licensing stage, where the category of the stem and affix are checked for compatibility, potentially localized in the left posterior temporal lobe (PTL) around 200-300ms; and [3] a semantic composition stage, where semantic well-formedness of the affix and the stem combination is examined, potentially localized in the left orbitofrontal cortex (OF) around 300-500ms. In both languages, greater brain activity was found in the left PTL for pseudowords with a verbal affix attached to a noun (*re-idea, syntactic category violation) than pseudowords with the same affix attached to a verb with the wrong argument structure (an unergative verb, *re-smile, argument structure violation), while the reversed activation pattern was observed in the left OF. However, both of these studies looked at derivational morphology. The present study investigates whether these three morphological processing stages and the brain activation associated with them are universal, and also triggered by Tagalog inflectional prefixes, na- and nag-, both marking agent voice and grammatically combine with verbal stems. Nag- requires an external argument and attaches to unergative and transitive verbs, and is therefore incompatible with unaccusative verbs; while na- attaches to unaccusative and transitive verbs, but is incompatible with unergative verbs (Nie, 2020). Methods/Design: 19 native Tagalog speakers participated in a visual lexical decision task with concurrent MEG recording. The task had three conditions: (a) grammatical items that correctly combine nag-/na- to verbal stems (nagsimula ‘started’); (b) syntactic category violation items was created by combining these affixes with stems that are unambiguously nouns (*nagpusa ‘catted’, *nabintana ‘windowed’); and (c) argument structure violation items was formed by attaching nag- to unambiguously unaccusative verbs (*nagguho ‘collapsed’), and na- to unambiguously unergative verbs (*naluksa ‘mourned’). Results: we found a significant correlation between stem:whole word transition probability (a measure of morphological complexity) and activity in the left VWFA between 100-150ms (p=0.024), suggesting that the grammatical items are decomposed into morphological units. Regression-based spatio-temporal cluster permutation tests revealed a significant cluster in the left PTL between 200-220ms, with argstrucviol condition showing greater activation than synviol condition. Finally, a marginally significant cluster emerged in the right OF between 357-387ms (p=0.056), with greater activation for synviol condition than argstrucviol condition. Overall, our findings support the three-stage morphological processing model and the role of left VWFA for decomposition, left PTL for syntactic category licensing, and OF during argument structure composition stage. This is the first such a study that looks at inflectional morphology in Tagalog, thereby adding ontological breadth to the existing literature. Note that the activation pattern is reversed in the present study compared to previous results from Greek and English, and the OF activation is right lateralized, thereby showing potential variability in the neural bases of complex word processing.
Topic Areas: Morphology,