Cross-linguistic transfer effects of verb-production therapy in two cases of multilingual aphasia

Background: Verb retrieval is challenging for monolingual and multilingual speakers with aphasia. Previous research on bilingual aphasia shows equivocal results of cross-linguistic transfer and inhibition.

Aims: This study explores the impact of verb-production treatment in the treated and untreated languages of two bilingual speakers with aphasia. The main goals were to explore treatment effects, possible cross-linguistic transfer effects and to investigate possible inhibition of the untreated languages.

Methods & Procedures: The participants were one trilingual speaker (Portuguese-Ronga-Norwegian) with nonfluent aphasia and one bilingual speaker (English-Norwegian) with fluent aphasia. They received two types of treatment: communication-based therapy and Semantic Feature Analysis. Treatment was conducted in Norwegian, a late-acquired language for both speakers. Treatment effects were measured in action naming tasks and narrative tasks in the treated language as well as the untreated languages.

Outcomes & Results: Overall, the participants responded positively to the verb production treatments. This was demonstrated at the lexical level and also in discourse production, especially in the treated, but also in the untreated languages. No inhibition of the untreated languages was found.

Conclusions: The data provide evidence for positive effects of verb-retrieval treatment provided in sentence contexts in a late-learned weaker language of multilingual speakers with aphasia. The treatments did not lead to an unwanted inhibition of the untreated language, which is an important finding for clinicians as well as for researchers. The results provide evidence for a shared conceptual network of the languages in bilingual speakers, supporting current models of bilingual language processing.