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Morphophonological alternations modulate early and automatic decomposition mechanisms in the visual word form area: MEG evidence from Tagalog prefixation
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Poster A34 in Poster Session A, Tuesday, October 24, 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
Previous cross-linguistic studies have found significant correlation between stem:whole word transition probability (TP, i.e., a measure of morphological complexity) and activity in the left visual word form area (VWFA) around 100-200ms after stimulus presentation, suggesting that morphologically complex words are subject to early, form-based decomposition mechanisms (e.g., Wray et al., 2022 in Tagalog; Stockall et al., 2019 in English; Ohta et al., 2019 in Japanese; Neophytou et al., 2018 in Greek). However, whether this early and automatic decomposition mechanisms is negatively impacted by morpheme boundary opacity due to morphophonological alternations remains an empirical question. The present study investigates if VWFA-based morphological decomposition is modulated by morphophonological alternations in Tagalog. Methods/Design: 19 native Tagalog speakers participated in a visual lexical decision task with concurrent MEG recording. The task had three conditions, all involving the prefixes paN- or maN-: (a) No-Change; words that do not exhibit morphophonological alternations (e.g., paN + halo ‘mixer’ = panghalo); (b) Nasal-ASSIMilated: the nasal N is pronounced as /m/ or /n/ to match with the place of articulation of the stem-initial obstruent (e.g., paN + pook ‘district’ = pampook); (c) Nasal-SUBStituted: the prefix-final nasal and the stem-initial obstruent are substituted by a single phoneme that is homorganic to the original obstruent (e.g., maN + palo ‘slap’ = mamalo). Nasal substitution makes the boundary between the prefix and stem opaque. The VWFA was localized using a task adapted from Gwilliams and Marantz (2016), where participants attended to stimuli from a 4x2 design: (1) a 4-letter Tagalog word, (2) a single letter, (3) a symbol, or (4) a string of symbols. Each were either (1) unmasked, or (2) masked by Gaussian noise. Localizer Results: we conducted a two-stage regression analysis in which regressions were fit at each time point and source point per-subject for factors of String Type (symbols, letters) and Stimulus Type (1-character string, 4-character string). Spatio-temporal cluster-based permutation tests were conducted in the bilateral occipitotemporal region over a 120-170ms time window. With 19 subjects, we found a significant cluster in the ventral occipitotemporal region (p = 0.038), with higher activation for letter/word than symbol, thereby replicating the canonical activation direction previously found in English, Greek, and Finnish. This brain cluster was subsequently used as a functional region of interest in the morphological decomposition analyses. fROI Results: we extracted the dSPM values averaged across space (the VWFA) and time (from 110 to 160ms) and used it as input for a mixed-effects model with TP and Condition as fixed factors. We found a significant interaction between TP and Condition (p=0.041), suggesting that the effects of TP on dSPM was not consistent across different morphophonological alternations. We further found that TP is significantly negatively correlated with dSPM for the No-Change condition, while no significant correlation was found for ASSIM and SUBS conditions. Overall, the present study finds that morphophonological alternations modulate the ease in which prefixed words are decomposed into morphological units in the VWFA by obscuring morpheme boundaries.
Topic Areas: Morphology, Reading