Absence of treatment generalization and cross-language transfer in bilingual phonological anomia

Background Phonological anomia is one of the most persistent consequences of stroke-induced aphasia. Understanding how phonological treatment outcomes generalize within and across languages is essential for designing effective bilingual interventions. In bilingual aphasia, cross-linguistic transfer and cognate facilitation are often expected but inconsistently observed.Aims This single-case study tested, in a balanced Basque – Spanish bilingual with post-stroke phonological anomia, whether intensive phonological therapy (i) generalized to untreated items within the treated language, (ii) produced cross-linguistic transfer, (iii) was influenced by cognate status, and (iv) was maintained approximately 4.5 months later.Methods & Procedures A two-phase multiple-baseline design was implemented. Therapy was delivered monolingually in two consecutive 4-week blocks (Phase 1 = Basque, Phase 2 = Spanish) using an item-specific phonological programme aligned with Phonological Component Analysis principles. A list of 200 translation-equivalent items was created; within each language, items were assigned to treated and untreated sets, which differed across languages. After each phase and at follow-up, the participant completed a naming-by-definition task in both languages. Planned contrasts using generalized linear mixed-effects models evaluated within-language generalization, cross-linguistic transfer, cognate effects, and maintenance, with results expressed as model-based estimated probabilities and effect sizes.Outcomes & Results Therapy produced reliable improvement for trained items in the language of therapy. No generalization occurred to untreated items within language or to the untrained language, including for cognates. At follow-up, Spanish-treated items showed partial decline relative to end-of-treatment, whereas Basque performance remained stable. At the follow-up session itself, treated-versus-untreated differences were not statistically reliable in either language.Conclusions When impairment is primarily phonological and therapy targets phonological form, gains appear item-specific and language-specific, with limited evidence for cognate-driven or cross-language transfer. Clinically, improvements in both languages require direct intervention in each and systematic maintenance planning. These findings inform models of bilingual lexical access and guide evidence-based rehabilitation strategies for bilingual individuals with aphasia.