We describe a case study of a French-Dutch bilingual patient with differential aphasia, showing clearly larger impairments in Dutch than in French. We investigated whether this differential impairment in both languages was due to selective damage to language-specific brain areas resulting in the "loss" of the language representation itself, or rather if it reflects an executive control deficit. We assessed cross-linguistic interactions (involving lexical activation in the most affected language) with cognates in a lexical decision (LD) task, and executive control using a flanker task. We used a generalized LD task (any word requires a "yes" response) and a selective LD task in the patient's two languages (only words in a given target language require a "yes" response). The cognate data unveil a differential pattern in the three tasks, with a clear cognate facilitation effect in the generalized LD tasks and almost no cognate effect in the selective LD tasks. This implies that a more impaired language can still affect the processing of words in the best-preserved language, but only with low cross-language competition demands (generalized LD). Additionally, the flanker task showed a larger congruency effect for the patient compared with controls, indicating cognitive control difficulties. Together, these results support accounts of differential bilingual aphasia in terms of language-control difficulties.
Keywords: aphasia; behavioral neuropsychology; bilingualism; cognates; cognition; control; differential aphasia; psycholinguistics.