The Influence of Aphasia Type and Severity on Sentence Comprehension after Left Hemisphere Stroke.

backgroundSentence comprehension relies on the integrity of a left-lateralized language network that is frequently disrupted following left hemisphere stroke. While comprehension deficits are well documented in Broca's and Wernicke's aphasia, less is known about how sentence comprehension varies across the broader aphasia spectrum, including types traditionally viewed as comprehension-intact, such as anomic and latent aphasia.

aimsThis study examined how sentence comprehension varies as a function of aphasia type and severity, with particular focus on comprehension of syntactically complex, non-canonical sentences. We also aimed to characterize comprehension in latent aphasia, an understudied group of stroke survivors who perform within normal limits on standardized assessments but report residual language difficulties. METHODS AND PROCEDURES: Eighty-five adults participated, including 64 individuals with left hemisphere stroke and 21 neurotypical controls. Sentence comprehension was assessed using a sentence-picture matching task containing canonical (subject-relative) and non-canonical (object-relative) sentences. Aphasia type (latent, anomic, Broca's, conduction) and severity (latent, mild, moderate, severe) were determined using the Western Aphasia Battery-Revised (WAB-R). Separate mixed-effects models were used to examine the effects of aphasia type, severity, and syntactic structure on comprehension accuracy and reaction time. OUTCOMES AND

resultsSentence comprehension accuracy declined with increasing aphasia severity. Agrammatic comprehension patterns-characterized by poorer performance on non-canonical than canonical sentences-were observed across all aphasia types, though the degree of impairment varied. The latent aphasia group performed better than the anomic group but worse than controls. The Broca's and conduction aphasia groups showed greater impairments than the anomic group but did not differ from each other. CONCLUSIONS AND IMPLICATIONS: Sentence comprehension deficits occur across a wide range of aphasia severities, including in individuals with latent aphasia who score above clinical diagnostic cutoffs. These results underscore the need to assess sentence comprehension across the full aphasia spectrum using syntactically complex sentences, which may help identify subtle impairments that impact functional communication. WHAT THIS PAPER ADDS: What is already known on this subject Sentence comprehension deficits in aphasia vary by severity and type, but prior studies have typically examined these factors separately and have rarely included individuals with latent aphasia who fall above diagnostic thresholds. As a result, it remains unclear how sentence comprehension varies across the full spectrum of aphasia. What this study adds to existing knowledge This study systematically examined how sentence comprehension accuracy and response times vary with both aphasia type and severity, across canonical and non-canonical syntactic structures. Findings demonstrate that comprehension deficits are more widespread than previously recognized, extending even to individuals with latent aphasia. What are the potential or actual clinical implications of this work? The results underscore the need for assessment tools that incorporate syntactically complex sentences to detect subtle comprehension deficits that may not be captured by standard tests. Tailoring intervention to an individual's syntactic comprehension profile may enhance treatment outcomes.