Investigation of Tense and Grammatical Agreement in the Speech of Persian Agrammatic Aphasics According to the Tree Pruning Hypothesis

Across most languages, verbs produced by agrammatic aphasics are frequently marked by syntactically and semantically inappropriate inflectional affixes. The present study focuses on tense and grammatical agreement in the speech of Persian agrammatic aphasics according to the Tree Pruning Hypothesis (Friedmann & Grodzinsky, 1997). We wanted to know whether or not all functional morphemes are equally affected in this syndrome. We hypothesized that tense features are more severely impaired than agreement inflection. So we evaluated two Persian agrammatic patients in this descriptive-analytic study. They were classified as agrammatic Broca's aphasics according to the Persian aphasia test. The spontaneous speech, verb completion task and sentence repetition task were also designed and performed. Our findings showed that tense features are more severely impaired than agreement inflection. Results did not indicate a significant difference between different aspects of the Past tense; there was a significant difference between the mean of responses to Past tense in comparison to Present tense and Future. Our findings showed that the impairment in use of Past tense was more than the other tenses. On the other hand, tense features were more severely impaired than agreement inflection. This is because in languages with a rich system of agreement inflections like Persian, the verb agreement is a phonological representation of agreement between subject and verbal head in a specific position called Inflection phrase. Subject-verb agreement errors may occur because there is no movement of verb from the head of the tense phrase to the head of the agreement phrase as a kind of head-to head movement. The general idea is that the selective pattern of impairment in Broca's agrammatic aphasia and the dissociations witnessed in tense and agreement use follows from the inaccessibility of high nodes of the syntactic tree to agrammatic speakers. This causes syntactic structures that relate to high nodes of the tree to be impaired in agrammatism, whereas lower structures are unimpaired. A retrospective examination of the literature shows that our findings are corroborated by others. These findings also bear upon central issues in linguistic theories, such as checking theory in Minimalist Program by Noam Chomsky (1992) and that of Pollock (1989), regarding split inflection.