Poster D41, Wednesday, August 21, 2019, 5:15 – 7:00 pm, Restaurant Hall
Lower LIFG activation for higher syntactic complexity: MEG evidence from conceptually-matched Arabic stimuli
Suhail Matar1, Julien Dirani2, Alec Marantz1,2, Liina Pylkkänen1,2;1New York University, 2NYU Abu Dhabi Research Institute
INTRODUCTION. During language comprehension, many different types of combinatory operations are tightly correlated, including conceptual-semantic and syntactic ones. While a consensus is emerging that the left anterior temporal lobe participates in some form of conceptual combination, the hypothesis space of the neural underpinnings of syntax remains relatively wide. Currently, prominent hypotheses range from the localization of the syntactic Merge operation to the LIFG (Zaccarella & Friederici, 2015), to the virtual inseparability of syntactic processing from other computations during comprehension (Blank et al., 2016). However, it is precisely this difficulty in experimentally isolating and manipulating syntax (while controlling for semantic variables and avoiding pseudo-language) that has posed a major paradigmatic challenge to the syntax question. Here, we used the grammatical properties of adjectival modification in Arabic in order to vary the size of a projected syntactic tree, while keeping conceptual combination identical. Specifically, by introducing or omitting (orthographically contiguous) determiners from noun-adjective combinations, we can create structurally smaller noun phrases (1a-b) and larger full sentences (1c) that all feature the same open-class lexical items: (1)a. Indefinite phrase – small structure: sha:ḥina ḥamra:’ (gloss: truck red) = ‘a red truck’; b. Definite phrase – small structure: al-sha:ḥina al-ḥamra:’ (gloss: THE-truck THE-red) = ‘the red truck’; c. Sentence – large structure: al-sha:ḥina ḥamra:’ (gloss: THE-truck red) ‘The truck is red.’ METHODS. In this MEG study, fifteen participants read grammatical phrases or sentences, as in (1). One third of the stimuli were followed by a task item: participants read a sentence with a gap, mentally filled the gap with the stimulus, and indicated whether the resulting sentence is grammatical and plausible. Our main aim was to identify activation sensitive to the phrase vs. sentence contrast, for which we tested four main ROIs typically cited in the syntax literature: LIFG, Angular Gyrus, LATL, and the posterior superior temporal cortex. Additionally, given the evidence suggesting the LATL is an integrative hub sensitive to conceptual -rather than syntactic- variables, we expected the combinations in (1a-c) to elicit more LATL activation than single-word controls (‘red’/’the-red’), but not to elicit significantly different levels of activation compared to one another. RESULTS. Replicating prior work on the LATL, all combinatory conditions in (1) showed increased LATL activation compared to single-word controls in an early time-window (140-200ms), with no modulation by the complexity of syntactic structure. In contrast, the LIFG’s pars opercularis was sensitive to syntactic complexity, but in the opposite direction than the one predicted by the Merge hypothesis: the syntactically simpler phrases generated more activation than the sentences (270-320ms). CONCLUSION. Our results show a dissociation between semantic and syntactic processing of minimal phrases and sentences. In the LATL, conceptual combination elicited more activation compared to single words, regardless of syntactic complexity. For syntactic processing, rather than syntactic structure building, the LIFG’s role appears to be different, perhaps reflecting structure projection, as has been recently proposed (Matchin et al., 2017): unlike our sentences, the noun phrases could be driving the anticipation or projection of upcoming syntactic structure.
Themes: Syntax, Meaning: Combinatorial Semantics
Method: Electrophysiology (MEG/EEG/ECOG)