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Poster A25, Tuesday, August 20, 2019, 10:15 am – 12:00 pm, Restaurant Hall

Composition without syntax or plausibility: LATL conceptual combination occurs in the absence of syntactic phrase closure or semantic plausibility

Alicia Parrish1, Liina Pylkkänen1,2;1New York University, 2New York University, Abu Dhabi Institute

The interplay of syntactic, logico-semantic and conceptual routines in sentence processing is a central question for the neurobiology of language. The combinatory role of the left anterior temporal lobe (LATL) has been relatively well characterized and appears to be conceptual in nature. At the same time though, the LATL also correlates with syntactic processing steps during narrative comprehension. Here we asked whether combinatory effects in the LATL can be obtained independent of syntax. -- METHODS -- 25 participants read sentences via RSVP in a picture verification task during a magnetoencephalography (MEG) recording. Critical stimuli were phrases in which (i) syntactic merge was blocked by word category cues on the modifier (‘pleasant sunny’ vs. ‘pleasantly sunny’), or (ii) syntactic closure of the highest phrasal node was blocked by number mismatch between a determiner and noun (‘these herbal tea’ vs. ‘this herbal tea’). We additionally manipulated the semantic plausibility of each combination, yielding the full paradigm of Semantic Plausibility x Syntactic Closure x Word Category (target word in brackets): (a) ‘this/these herbal [tea] drinker(s)…’ (plausible, closure/non-closure, noun); (b) ‘this/these impolite [tea] drinker(s)…’ (implausible, closure/non-closure, noun); (c) ‘pleasantly/pleasant [sunny] days…’ (plausible, closure/non-closure, adjective); (d) ‘sharply/sharp [sunny] days…’ (implausible, closure/non-closure, adjective). If conceptual combination is sensitive to morphological agreement or animacy cues and only occurs once a predicted syntactic/semantic feature becomes available, then (i) a sentence with syntactic agreement mismatch will fail to combine ‘herbal’ with ‘tea’ due to the lack of a predicted plural feature, and (ii) a semantically implausible sentence will fail to compose due to a mismatch in predicted animacy features. Non-combinatory control conditions were included using numeral modification (“one tea”, “two tea”), as this environment has been shown not to elicit an early LATL combinatory effect. -- RESULTS -- [LATL composition effect]: Across all experimental stimuli, we observed increased activity in a significant spatiotemporal cluster widely distributed within the LATL at 200-290ms for all critical target words as shown in (a-d) as compared to the non-combinatory controls (p = 0.028). Thus the LATL composition effect occurred both in the absence of plausible meaning and closure of the largest syntactic phrase. [Plausibility effect]: For noun stimuli, we observed an increase in activation for the Implausible condition in posterior temporal cortex (190-320ms, p = 0.03), indicating that the parser was sensitive to the plausibility manipulation. [Agreement mismatch effect]: We found greater activation for the syntactic-mismatch condition compared to the non-mismatched condition in LIFG at 390-430ms (p = 0.04) and left STC 350-430 (p = 0.025), an effect much later than the conceptual composition effect. [Word category effect]: The largest word category effect was observed in the Left Angular Gyrus, with greater activation for nouns compared to adjectives at 130-230ms (p <0.01). -- CONCLUSION -- Effects of conceptual composition in the LATL occurred despite contradictory evidence from earlier semantic and syntactic feature-based predictions. This study supports a processing model where LATL composition is blind to syntax and to the local plausibility of the combination.

Themes: Meaning: Combinatorial Semantics, Syntax
Method: Electrophysiology (MEG/EEG/ECOG)

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