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This study investigates the neural processing of context-based language comprehension in persons with aphasia (PWA) by examining three event-related potential (ERP) components: the N400, anterior post-N400 positivity (aPNP), and posterior post-N400 positivity (pPNP). Language comprehension in PWA often involves prediction difficulties, which are integral to understanding within contextual constraints. Despite the extensive use of ERPs in psycholinguistic research, the application of ERP components beyond the N400 in PWA remains limited. The N400, typically reflecting semantic retrieval and sensitive to context predictability, is known to be diminished in PWA, potentially indicating reduced efficiency in accessing lexical-semantic information. In contrast, the aPNP and pPNP, which reflect higher-level comprehension processes, have been explored primarily in neurotypical populations.
This study utilized a self-paced reading rapid serial visual presentation (RSVP) paradigm. A 2x3 mixed design was used, comparing PWA with neurotypical adults across three conditions: expected, unexpected, and anomalous words. ERP outcomes included mean amplitudes and latencies for the N400, aPNP, and pPNP components, analyzed through linear mixed-effects models. Behavioral data on reading times were also collected as a secondary outcome measure.
The N400 response in PWA was reduced in amplitude compared to controls, accompanied by an anterior shift in scalp topography and a trend toward delayed latency, suggesting impaired semantic processing despite no significant interaction effects. Using an a priori ROI, the aPNP was not statistically significant, however, the scalp topographies were consistent with the expected distribution of this effect. The pPNP response was absent in PWA, reflecting challenges in integrating anomalous words within sentence context. Behavioral results aligned with ERP data, with PWA exhibiting significantly longer reading times and lower plausibility judgment accuracy. Correlations between aphasia severity (Aphasia Quotient, AQ), naming abilities, and ERP measures were weak but consistent with reduced semantic access and re-evaluation capabilities in PWA who are more severe.
Overall, this study’s findings emphasize unique neural and behavioral patterns in PWA, underscoring the potential of N400, aPNP, and pPNP components as biomarkers in aphasia research. Future work should further explore these components’ roles in adaptive language processing to inform more targeted prospective treatment approaches for PWA.