Finite verb inflections for evidential categories and source identification in Turkish agrammatic Broca's aphasia

This study presents the pioneering data on the neurological representation of grammatically marked evidentials with regard to their dissolution in agrammatic Broca's aphasia. Across two tasks, we investigated the production of finite verb inflections for evidential categories and identification of the information sources these evidential categories are mapped on in Turkish individuals with agrammatic aphasia. In Turkish, information source is grammatically marked for three different past contexts: direct perception, reportative, and inferential. The following research questions were explored: (1) is inflection for different evidential categories equally affected in Turkish agrammatic aphasia? (2) Is identifying the categories of information source impaired? Turkish agrammatic speakers and non-brain-damaged speakers (NBDs) were tested with a production and a source identification tasks. Our findings demonstrate that in Turkish agrammatic speakers the direct perception evidential was more affected in production than the inferential and reportative evidentials. However, the agrammatic speakers retained the ability to identify the source for the direct perception. We argue that information source values conveyed by evidential forms are impaired in agrammatic aphasia. These findings are discussed on the basis of earlier studies to time reference and tense in agrammatism.