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

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.

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.

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.

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.