Bilingual aphasia: How “parallel” is impairment? Insights from picture naming.

Background: The assessment of aphasia in bilingual speakers is challenging, requiring consideration of both the linguistic impairment and multiple bilingualism–related characteristics of the individual (e.g. proficiency, dominance, age of onset of bilingualism). Yet it is essential that we rise to this challenge. We focus on the extent to which both languages of a bilingual are impaired similarly, namely have a ‘parallel impairment’. We examine this phenomenon in spoken word production going beyond analyses of accuracy, to investigate whether error patterns are also parallel across languages. Aims: Through analysis of the spoken picture naming performance of a series of bilingual speakers with aphasia, we aimed to address the hypothesis as to whether -when accuracy and error patterns differ across languages- this indicates different impairments in each language or instead reflects the interaction between bilingualism-related factors and a single underlying deficit. Methods & Procedures: Eight bilingual speakers with post-stroke aphasia were recruited with varying language combinations, and ages of onset of bilingualism, language dominance and proficiency. All showed lexical-semantic impairments in spoken word retrieval. Participants completed a spoken picture naming task in both their languages. Naming performance was analysed examining accuracy and error types across languages, and the psycholinguistic variables affecting accuracy and a detailed analysis of error types produced. Outcomes & Results: Seven participants showed significant differences in naming accuracy between languages, with six performing better in their dominant language regardless of whether it was their first or second language. One participant with balanced dominance showed higher accuracy in their first, more proficient, language. Significant effects of psycholinguistic variables on accuracy were generally consistent across languages. Seven participants showed differences in error distributions across languages. Non-target language errors (producing words from the unintended language) were more frequent in the non-dominant language for five participants. Phonological errors were more frequent in the second language for five participants, while semantic error distributions were largely similar across languages. Conclusions: Our examination of picture naming outcomes across languages found evidence for differences in naming accuracy and error patterns across languages. However, these differences could be explained by bilingualism-related factors such as language dominance, proficiency and age of onset of bilingualism. We conclude that the nature of impairment in word retrieval in bilinguals with aphasia is indeed ‘parallel’ which reinforces the importance of detailed bilingual profile assessments in all languages and greater emphasis on analysis beyond accuracy to evaluate the different error types produced.