Phonological and semantic skills predict past tense verb inflection ability in perisylvian aphasia

Background: Although verb inflection is often impaired in post-stroke aphasia, the contribution of underlying cognitive/linguistic skills to correctly inflect different types of verbs is not well understood. Aims: This study examined the degree to which empirically derived factors that reflect core language skills predict generation of past tense for regular (e.g., slapped), weak-irregular (e.g., slept) and strong-irregular (sang) verbs, and explored the neural substrates that support these skills. Methods & procedure: Fourteen individuals with chronic post-stroke aphasia completed comprehensive assessments that included measures of phonological and semantic skills and a past tense verb inflection task using regular, irregular, and pseudo-verbs. Principal component analyses were implemented to derive underlying cognitive linguistic factors. The resulting factor scores were entered into regression analyses to examine the prediction of verb inflection performance. Exploratory voxel-based lesion symptom mapping was conducted to identify brain regions where lesion was associated with impaired processing of phonology, semantics, and past-tense verb inflection. Outcomes & results: Results indicated that phonological skills predicted accuracy of past tense production for all verb types (regular, weak-irregulars, strong-irregulars, and pseudo-verbs), and semantic ability also contributed to performance on strong-irregular verbs (i.e., verbs that are not marked by the final lingua-dental phoneme). Thus, the inflection of verb stems to past tense forms reflected differential reliance on underlying phonological and semantic skills. Consistent with behavioral results, voxel-based lesion symptom mapping analyses showed that damage to left frontal and temporal brain regions that support phonology and semantics was associated with impaired past-tense inflection.