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Production and comprehension of reference of time in Swahili–English bilingual agrammatic speakers

Background: Several studies on time reference show that monolingual agrammatic speakers have difficulty producing and/or comprehending verb forms referring to past events or actions. The PAst Discourse LInking Hypothesis (PADILIH) has been formulated to account for this phenomenon (Bastiaanse et al., 2011). In the current study on bilingual aphasia we examine whether time reference problems, especially reference to the past, extend to both languages of bilinguals with agrammatic aphasia. The two languages, Swahili and English, have different verb morphology for expressing reference of time. Aims: The current study tested the production and comprehension of reference of time through verb morphology in two languages of Swahili–English bilingual agrammatic speakers. Methods & Procedures: A total of 13 agrammatic speakers and 13 non-brain-damaged individuals were tested using an adaptation of the Test for Assessing Reference of Time (TART; Bastiaanse, Jonkers, & Thompson, 2008; Swahili version: Abuom & Bastiaanse, 2010). Reference to the past, present, and future conditions were examined through a sentence-completion and a picture–sentence-matching task. Outcomes & Results: While the non-brain-damaged participants performed at ceiling in both languages, the agrammatic individuals' performance showed a selective deficit of reference to the past on both comprehension and production tasks. A similar pattern was observed in the two languages in spite of the structural differences. Conclusions: The PAst Discourse LInking Hypothesis (PADILIH) was supported by these results. Furthermore it has been revealed that time reference deficits extend to both tested languages of bilingual speakers with agrammatic aphasia regardless of the structure of languages mastered pre-morbidly. The implications of these findings for the theories of bilingual agrammatism are discussed.