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At-a-glance sentence comprehension involves bottom-up composition in left inferior temporal cortex and top-down composition in middle posterior temporal cortex at 300-450ms
Poster E45 in Poster Session E, Thursday, October 26, 10:15 am - 12:00 pm CEST, Espace Vieux-Port
Nigel Flower1, Liina Pylkkänen1,2; 1New York University, 2NYUAD Institute, New York University Abu Dhabi
Although natural reading typically involves eye movements, skilled readers are also able to understand messages that are flashed quickly, such as notifications on a phone or messages on the road. A growing psycholinguistic literature has provided evidence of rapid sentence composition in such circumstances with a technique called rapid parallel visual presentation (RPVP; Snell and Grainger, 2017; Massol et al., 2021). However, the neural mechanisms of such rapid combinatory computations are not yet understood. The behavioral RPVP evidence shows that subjects perform better when all words in a stimulus form a grammatical sentence as opposed to an ungrammatical string, a so-called Sentence Superiority Effect (Snell and Grainger, 2017). Additionally, subjects often miss errors when presented with sentences that contain an inner transposition such as you that read wrong (Mirault et al., 2018). In our MEG experiment, we sought to characterize the earliest neural correlates of the sentence superiority effect. Our main goal was to assess whether at that stage, neural signals would also “miss” an inner transposition, meaning that such errors would pattern with grammatical sentences due to top-down impact of grammatical knowledge, or whether inner transpositions would diverge from grammatical sentences, indicating a more detailed, bottom-up analysis. Using RPVP, we presented 25 participants with four-word sentences that were either fully grammatical (all cats are nice), contained an inner transposition between the second and third words (all are cats nice), or contained two transpositions resulting in a backwards sentence (nice are cats all). A spatiotemporal clustering ANOVA was performed over the entire left and right hemispheres to identify the neural correlates of sentence superiority and sensitivity to the transpositions. The clustering analysis revealed two significant activity clusters in the left hemisphere, and none in the right hemisphere, suggesting strict left laterality. The first cluster showed a two-way distinction between the grammatical (no-transpositions) and the ungrammatical (one or two transpositions) sentences and localized to the left anterior and inferior temporal regions around 310ms to 400ms after stimulus onset. This effect conformed to our bottom-up hypothesis. Its localization was also consistent with prior findings on rapid bottom-up composition that shows sensitivity to the form typicality of the stimulus (Flick and Pylkkänen, 2021; Matar et al., 2021). But we also identified a second cluster, localized in the left posterior temporal lobe (LPTL), with greater activity for the grammatical and one-transposition conditions as compared to the two-transposition sentences at 375 - 440ms after stimulus onset. This effect patterned according to our top-down hypothesis, with a localization consistent with prior proposals about the neural basis of top-down syntactic predictions (Matchin et al., 2017). In sum, we discovered that the early stage of comprehending a rapidly flashed full sentence contains both a bottom-up and a top-down mechanism, with the bottom-up mechanism emerging first in inferior temporal cortex and the top-down mechanism immediately following in posterior temporal cortex.
Topic Areas: Syntax and Combinatorial Semantics,