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MEG evidence for ultrarapid phrase structure detection at 100-200ms in parallel visual presentation
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Poster E40 in Poster Session E, Thursday, October 26, 10:15 am - 12:00 pm CEST, Espace Vieux-Port
Jacqui fallon1, Liina Pylkkänen1,2; 1New York University, 2New York Univeristy Abu Dhabi
While in speech, linguistic input enters our brains slowly, through the visual modality we can also comprehend entire sentences from a 200ms rapid parallel visual presentation (RPVP; Snell & Grainger, 2017). RPVP research on short sentences has identified a so-called “sentence superiority effect" (SSE), defined as facilitated processing for grammatical as compared to scrambled sentences, indicating rapid detection of sentence structure from parallel input. In RPVP, processing is not constrained by any temporal order in the input, which allows us probe the brain's inherent way of ordering computations. We tested whether the earliest neural correlates of the SSE reflect syntactic processing, such as rapid phrase structure detection akin to Phase 1 in Friederici (2002), or an early stage of combinatorial semantic processing, as observed in MEG studies of minimal phrases (Pylkkänen, 2019). Stimuli consisted of Subject-Verb-Object (SVO) sentences, semantically related and unrelated noun lists, and pseudoword lists. The sentences were also presented with noun-verb agreement errors, thematic role reversals, and as object relative clauses. During an MEG recording, participants saw 300ms flashes of the stimuli followed by either a sentence identical to the stimulus, or a sentence with one word replaced by a length-matched, semantically plausible substitution. Participants indicated via button press whether the second sentence was the same as the first. Results yielded a clear behavioral SSE with faster and more accurate matching responses for the grammatical SVO sentences as compared to all list stimuli, including related lists. For a neural SSE, a spatiotemporal clustering analysis revealed two clusters of increased source-localized MEG activity for grammatical SVO sentences over lists in left posterior temporal cortex as early as 111-221ms, and later in left superior temporal and inferior parietal cortices at 195-285ms. To query what type of processing these effects reflect, we tested whether they would replicate if the sentence was replaced by an erroneous stimulus containing an agreement error or a role reversal, or by a syntactically more complex relative clause. For the earlier cluster, the agreement violations and role reversals replicated the effect, but relative clauses did not. This suggests a rapid sketch of phrase structure with no encoding of agreement or thematic roles, since violations of these aspects of the representation did not affect the activity. Further, since the effect did not obtain for the object relative clauses, it appears that the underlying mechanism is unable to compute this more complex structure. The earlier effect also disappeared for double violations of agreement and thematic roles, suggesting that these stimuli were no longer sufficiently sentence-like. In contrast, the second, later SSE effect replicated for all sentence types, leaving open the possibility that it could be driven by the sheer presence of a verb. This study provides a spatiotemporal localization of rapid sentence comprehension for a short visually presented full sentence. Our results suggest that the first stage of this process involves a quick sketch of basic phrase structure with syntactically canonical word order, more in line with Friederici (2002) than Pylkkänen (2019).
Topic Areas: Syntax and Combinatorial Semantics,