Cognate effects and cognitive control in patients with parallel and differential bilingual aphasia

Until today, there is no satisfying explanation for why one language may recover worse than another in differential bilingual aphasia. One potential explanation that has been largely unexplored is that differential aphasia is the consequence of a loss of language control rather than a loss of linguistic representations. Language control is part of a general control mechanism that also manages non-linguistic cognitive control. If this system is impaired, patients with differential aphasia could still show bilingual language activation, but they may be unable to manage activation in non-target languages, so that performance in another language is hindered.To investigate whether a loss of cognitive control, rather than the loss of word representations in a particular language, might underlie differential aphasia symptoms.We compared the performance of seven bilinguals with differential and eight bilinguals with parallel aphasia with 19 control bilinguals in a lexical decision and a flanker task to assess bilingual language co-activation and non-linguistic control respectively.We found similar cognate effects in the three groups, indicating similar lexical processing across groups. Additionally, we found a larger non-linguistic control congruency effect only for the patients with differential aphasia.The present data indicate preserved language co-activation for patients with parallel as well as differential aphasia. Furthermore, the results suggest a general cognitive control dysfunction, specifically for differential aphasia. Taken together, the results of the current study provide further support for the hypothesis of impaired cognitive control abilities in patients with differential aphasia, which has both theoretical and practical implications.