Cortical tracking reveals disrupted syntactic processing dynamics in aphasia

Sentence comprehension requires the rapid construction of hierarchical structure and the integration of non-adjacent dependencies under working-memory constraints. Many people with aphasia (PWA) show difficulty comprehending syntactically complex sentences, yet the neural mechanisms underlying these deficits remain unclear. We examined cortical tracking of two distinct syntactic computations-hierarchical constituent closure (node count) and dependency integration cost-using EEG during a sentence-picture matching task. PWA and neurologically healthy controls listened to subject- and object-relative clause sentences varying in semantic reversibility. Neural alignment with each syntactic predictor was quantified using a conditional mutual information approach controlling for speech acoustics. Node count tracking was stronger for reversible sentences across groups, consistent with increased structural parsing under thematic ambiguity, and node count peaks were wider for PWA than controls specifically for reversible sentences, suggesting more prolonged constituent closure processing. Integration cost tracking was greater for object-relative clauses and exhibited delays under higher retrieval demands. PWA showed significantly earlier integration cost peaks overall, and earlier integration cost latencies predicted poorer comprehension accuracy for reversible object-relative clauses-the condition placing the greatest demands on dependency formation without semantic support. This relationship was consistent at the trial level, with all PWA showing shorter latencies for incorrect than correct responses. Integration cost latency predicted online comprehension accuracy but not performance on a standardized clinical assessment, suggesting that the timing of neural alignment with integration cost captures online dependency-resolution demands not fully reflected in global clinical measures. These preliminary findings highlight the potential of neural tracking measures to reveal structure-specific processing differences in aphasia.