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Evidence for a syntactic production-comprehension asymmetry in post-stroke aphasia

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Poster B56 in Poster Session B, Tuesday, October 24, 3:30 - 5:15 pm CEST, Espace Vieux-Port

Jeremy Yeaton1, Danielle Fahey2, William Matchin3, Gregory Hickok1; 1University of California, Irvine, 2University of Montana, 3University of South Carolina

Despite decades of research on the relationship between expressive and receptive agrammatism in people with aphasia (PWA), very little recent work has been done on the relationship between expressive paragrammatism and syntactic comprehension deficits (Eling et al., 1987). Here we compare behavioral patterns of sentence production with a measure of syntactic comprehension. By contrast to expressive agrammatism which is characterized by the reduction or omission of syntactic structures leading to “telegraphic speech”, paragrammatism is characterized by long utterances with more-than-necessary morpho-syntactic structure, and deficits in the hierarchical organization of sentences (Kleist, 1914). The two syndromes also have distinct lesion correlates, with expressive agrammatic participants having lesions in the left middle and inferior frontal gyri, and paragrammatic participants having lesions in the left posterior superior and middle temporal gyri (Matchin et al., 2020). PWA displaying expressive agrammatism tend to have relatively spared syntactic knowledge and comprehension (Linebarger et al., 1983), however to date, no work has investigated the relationship between paragrammatic output and syntactic comprehension. As such, it remains to be seen whether a) paragrammatism is constrained to the production domain, b) a paragrammatic production deficit entails a corresponding comprehension deficit, or c) depending on lesion location, paragrammatism can dissociate or co-occur with a comprehension deficit. These questions play a crucial role in distinguishing cortical models of syntax which rely on partially distinct circuits for production and comprehension (e.g.: Matchin and Hickok, 2020) from those that don’t (e.g.: Hagoort, 2016), or those which argue for a distributed rather than localized syntactic system (Fedorenko et al., 2020). Using a recently-developed error coding scheme (Fahey et al., 2022), the speech of 53 PWA retelling the story of Cinderella was characterized according to the proportion of agrammatic, paragrammatic, or grammatical utterances they produced. We used the Sequential Commands subscore of the Western Aphasia Battery (WAB-R; Kertesz, 2007) as a proxy measure for syntactic comprehension. We then carried out a voxel-based lesion-symptom mapping analysis to determine the relationship between lesions leading to paragrammatic errors and syntactic comprehension scores. We found a significant correlation between proportion of paragrammatic errors and syntactic comprehension scores (r = −0.292, p < 0.05). Critically, however, some participants with high proportions of paragrammatic errors scored at or near ceiling in the syntactic comprehension task. We found that distinct lesions in the posterior temporal lobe (PTL) corresponded to paragrammatic production and syntactic comprehension deficits. Thus, despite a significant negative correlation between paragrammatic production and syntactic comprehension, we did not find that syntactic comprehension deficits always co-occur with paragrammatic production. This relationship between paragrammatic production and syntactic comprehension is explained by their nearby lesion correlates in PTL which is consistent with previous findings on the lesion correlates of syntactic comprehension (Matchin et al., 2022; Yu et al., 2022). This organization would provide a reasonable candidate locus for the lemma system posited by Matchin and Hickok (2020) or correspond to different aspects of the message-structure interface proposed by Krauska and Lau (2023)’s non-lexicalist framework.

Topic Areas: Disorders: Acquired, Language Production

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