Transfer of Treatment Effects Between Languages in Bilingual Agrammatic Aphasia: A systematic review

Aphasia, a language disorder caused by damage to language regions in the brain, can have profound effects on a person’s communication. For speakers of multiple languages, bilingual aphasia research has demonstrated that treatment in one language can transfer to a non-treated language (Faroqi-Shah & Chengappa, 1996; Paradis, 1993). This systematic review evaluates research on bilingual aphasia to discuss: which grammatical structures can exhibit cross-linguistic transfer of treatment effects, including a) sentential structuring, b) morphosyntax, and/or c) lexical category access? The review produced 131 articles fitting the inclusion criteria, but only 12 addressed cross-linguistic transfer. Each study’s quality was scored for their description of the following factors: bilingualism description, aphasia diagnostic characteristics, linguistic description of errored structures, and statistics. Across all sources, quality indicators were included 97.9% of the time for bilingualism, 74.0% of the time for aphasia factors (most frequently excluding discussion of syntactic comprehension deficits), 92.0% of the time for linguistics, and 50% of the time for statistics. Most of the literature utilized a single-subject multiple baseline design, which did not meet the statistics quality indicator for experimental sampling. Although cross-linguistic transfer has been demonstrated for a) sentential structures b) morphosyntax and c) lexical category access, small samples and variations in treatment approaches, assessments, and participants’ language backgrounds limit generalizations. Larger studies of transfer effects are necessary and could lead to improved treatment outcomes for bilinguals with aphasia. As resources are often limited for treatment in a person’s native language, understanding transfer effects is key to providing comprehensive care.