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The neural bases of morphological inflection in bilinguals
Poster Session B, Friday, September 12, 4:30 - 6:00 pm, Field House
Xuanyi (Jessica) Chen1, Esti Blanco-Elorrieta1; 1New York University
Morphological inflection is central to successful language use. However, languages differ widely in their inflection systems and in the phonological forms those inflection processes take. Theories of bilingual language organization are yet to adjudicate whether bilingual individuals rely on the same neural substrates to compute inflection across languages. One possibility is that once the mind/brain develops a mechanism for morphological inflection in one language, it will always be recruited for the same computation regardless of the language that computation is performed in (The Unified Competition Model, MacWhinney, 2022). Alternatively, bilinguals may necessitate distinct mechanisms for morphological inflection in each of their languages (Shallow Structure Hypothesis, Clahsen & Felser, 2018). The first hypothesis is particularly intuitive when languages share the same distinctions and forms for a particular morphological process (e.g., plural +s), since it would seem redundant to develop distinct processing mechanisms for the same purpose. In contrast, the latter hypothesis could be intuitively appealing in cases where each language has distinct morphological instantiations (e.g., gender marking vs not). To address this question, we collected magnetoencephalography (MEG) data from 23 Spanish-English bilingual participants during a phrase-completion task designed to elicit morphological inflection. Participants viewed a visually presented noun (e.g., "boat") followed by an auditory cue initiating a phrase (e.g., hearing "two" after reading "boat"). They were then required to complete the phrase aloud (e.g., responding "boats"). This paradigm required participants to either inflect the noun or simply repeat it, depending on the auditory prompt. Critically, Spanish and English share similar number inflection systems, marking singular and plural using three phonologically identical forms (+s, +es, and +ø). This allowed us to orthogonalize phonological realization from morphological processing within and across languages to characterize i) when and where morphological inflection is computed in the bilingual brain, ii) whether the same neural bases compute this process across languages, and iii) whether the same neural processes are recruited for the overt (-s and -es) and the covert (+ø) morphological markers. We performed permutation-based spatiotemporal ANOVAs to understand the neural computation of morphological inflection i) across different languages, and ii) in overt vs. covert realizations. We identified an effect of inflection in the inferior frontal and anterior temporal lobes between 300-400ms after the offset of the auditory cue, with higher activation for inflection trials compared to repeat trials. This effect was shared across languages, and was independent of the phonological form the inflection took. We also found a main effect of inflection type across languages in the inferior frontal lobe (100ms), where overt inflection (+s and +es) elicited increased activity over the covert inflection (+ø). This result provides evidence to support theories of bilingual language organization that posit shared neural substrates across languages and finds evidence for abstract morphological inflection, even in the absence of a phonological realization.
Topic Areas: Multilingualism, Morphology