Cross-language generalisation in bilingual aphasia: what are we missing when we do not analyse discourse?

Background: Cross-language generalisation has been reported in about half of all published cases of bilingual aphasia treatment. However, many of those studies report data from only single-word naming tasks. In unbalanced bilinguals with aphasia, treating the post-morbidly less proficient language may result in apparent improvement to only the treated language. Aims: To investigate whether when tools are used to measure language abilities beyond the single-word and sentence levels, such as analysing discourse production, improvement in the post-morbidly more proficient language may be observed. Methods & Procedures: A Hebrew-English bilingual person with mild-moderate non-fluent agrammatic aphasia was recruited. He received 36 h of Verb Network Strengthening Treatment (VNeST) in English only, with pre- and post- treatment assessment of his language abilities in both English and Hebrew. Outcome & Results: Significant improvement was observed in the treated language (English) for noun and verb retrieval in object and action picture naming and within sentence production, but not for the untreated language (Hebrew). In discourse, greater and more widespread improvement was observed in the untreated language (Hebrew) than in the treated language (English). Conclusions: We advocate for more wide-ranging measurement tools in the field to reduce the risk of missing valuable information regarding generalisation. Only with a more representative understanding of the effects of language treatment in bilinguals with aphasia can we better understand the mechanisms behind cross-language generalisation.