Selective Impairment in Verb Inflection: Evidence from Persian Agrammatism

Impaired morpho-syntactic production is the hallmark of agrammatic aphasia. It has been shown across several languages that verb inflection is difficult for agrammatic aphasic speakers. Many studies have indicated that this deficit is selective. Agreement is relatively preserved, while tense is severely impaired. The present work is based on Interpretable Features' Impairment Hypothesis (Fyndanis, 2012) which believes that categories with uninterpretable features (e.g. Agr) are better preserved than categories with interpretable features (e.g. Tense & Aspect). It is argued that the increased processing demands of Tense and Aspect, which carry interpretable features, render them more vulnerable compared to Agreement, which bears an uninterpretable feature and is a local, strictly grammatical operation. A sentence completion task tapping subject-verb agreement and tense and a picture description task were administered to two native speakers of Persian with agrammatic aphasia. The patients were classified as Broca's aphasics according to the Persian aphasia test, their MRI reports and CT Scans. They were asked to participate in a battery of tests designed to assess their abilities in production of inflectional morphology. Results showed that all the agrammatic speakers performed as hypothesized. Overall, the tense was significantly more impaired than agreement.