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Syntactic vs. semantic computation in posterior temporal lobe: an MEG study on Bangla nominal prefixes.
Poster E29 in Poster Session E, Thursday, October 26, 10:15 am - 12:00 pm CEST, Espace Vieux-Port
Swarnendu Moitra1, Dustin A. Chacón2, Linnaea Stockall1; 1Queen Mary University of London, 2University of Georgia
Reading morphologically complex words involves at least two distinct stages of interpretation (Manouilidou & Stockall 2014; Schreuder & Baayen 1995). The first stage involves verification of the stem's syntactic category (*re-flat, re-make). The second focuses on evaluating the semantic compatibility of the affix and stem (*re-smile, re-make). Violations of syntactic category restrictions are faster to reject compared to semantic violations. Left posterior temporal lobe activation increases for syntactic category violations around 200–300ms, and orbitofrontal cortex activation increases for semantic category violations around 350–400ms. However, these studies have been conducted primarily in European languages written with an alphabet (English, Greek). We extend this paradigm to Bangla, an understudied non-European language written in abugida. Furthermore, previous studies have examined deverbal morphology, whereas here was focused on nominal derivational morphology. In contrast to previous findings, we found that posterior temporal lobe activity increases for semantic violations in Bangla. [METHODS] N=22 Bangla speakers participated in a lexical decision task, while brain activity was recorded with a 208 axial gradiometer MEG. Stimuli included morphologically complex, grammatical stimuli with prefixes prôti- and duḥ-. These prefixes attach to nouns with abstract senses, and imply a reversal of a process (prôti-; prôti-hiṁsa 'violence' = 'revenge') or add negative affect (duḥ-; duḥ-+ghôṭôna 'event' = 'accident'). Syntactic Category violations included prôti- and duḥ- attached to adjectival stems (*prôti-kalo 'black'). Semantic Category violations included prôti- and duḥ- attached to nouns with a main concrete sense (*prôti-rôktô 'blood'). [RESULTS] We conducted two-stage regression analyses, in which regressions were fit to each time and source point. Significant clusters were identified using spatio-temporal cluster-based permutation tests on the t-statistic from one-sided t-tests on regression beta values. We conducted regressions with factors Prefix × Condition over left temporal lobe from 200–300ms, and orbitofrontal cortex from 300–500ms. Stronger activation was elicited by Semantic Violations, 173–197ms, in the left posterior temporal lobe (p = 0.05). The orbitofrontal cortex analysis revealed an interaction between Prefix × Condition, 330–342ms, such that Semantic Violations with prôti- elicited greater activity (p < 0.01). [CONCLUSION] Our findings reveal a similar spatial and temporal profile to previous MEG studies on morphological decomposition in English and Greek (e.g., Manouilidou & Stockall 2014). However, in contrast to previous findings, our results show that posterior temporal activity is more responsive to semantic violations, and the subsequent orbitofrontal activity shows a more complex pattern. We suggest that these results could arise from some property of the morphological properties of Bangla and prôti- and duḥ-, both of which are fossilized prefixes from Sanskrit. More likely, we suggest that the concrete/abstract distinction is faster to access than the kinds of semantic restrictions previous studies have investigated (e.g., repeatable state of an internal argument); supporting this, previous EEG findings reveal distinctions between concrete and abstract nouns ~200–400ms (Holcomb, Kounios, Anderson, & West 1999). If the nature of the semantic violation explains the difference between Bangla nominal prefixes and English/Greek deverbal affixes, then the posterior temporal lobe activity may not necessarily index syntactic computation.
Topic Areas: Morphology,