Grammatical Parallelism in Aphasia Revisited

EasyChair Preprint 6557

Abstract

Classical models of language in the brain posit that damage to inferior frontal cortex impairs speech production, resulting in nonfluent aphasia with preserved comprehension, whereas damage to posterior temporal cortex results in fluent aphasia, impairing both comprehension and production. In the 1970s, a distinct and influential grammatical parallelism hypothesis emerged: that expressive agrammatism and syntactic comprehension deficits coincide, resulting from common injury to inferior frontal cortex. However, Matchin & Hickok (2020) advocate an alternative hypothesis: syntactic comprehension deficits coincide with paragrammatism (syntactic errors rather than overall reduction of grammatical complexity), resulting from common injury to the posterior temporal lobe. Here we tested both parallelism hypotheses. In 218 people with chronic left hemisphere stroke, we assessed syntactic comprehension by combining the Sequential Commands sentence comprehension subtest with the Auditory Word Recognition subtest as a covariate. A subset of 53 subjects were previously assessed for grammatical production deficits using consensus perceptual ratings by four expert raters of elicited speech samples. Paragrammatism (but not agrammatism) was associated with significantly worse syntactic comprehension. Damage to regions associated with paragrammatism (but not agrammatism) was associated with worse syntactic comprehension. Overlap analyses revealed no overlap between the regions implicated in agrammatism and syntactic comprehension, whereas there was substantial overlap in the regions implicated in paragrammatism and syntactic comprehension (in posterior superior temporal lobe). Our results speak against the grammatical parallelism hypothesis rooted in expressive agrammatism and damage to inferior frontal cortex, and in favor of the grammatical parallelism hypothesis rooted in paragrammatism and damage to the posterior temporal lobe, converging with the classical model.

Keyphrases: Lesion-symptom mapping, Paragrammatism, agrammatism, aphasia, sentence comprehension, syntax

@booklet{EasyChair:6557,
  author    = {William Matchin and Alexandra Basilakos and Brielle Stark and Dirk-Bart den Ouden and Julius Fridriksson and Gregory Hickok},
  title     = {Grammatical Parallelism in Aphasia Revisited},
  howpublished = {EasyChair Preprint 6557},
  year      = {EasyChair, 2021}}