Losing control of your languages: a case study.

Bilingual speakers are usually quite good at restricting their lexicalization output to the desired language while preventing all sorts of language intrusions from the language not in use. However, brain damage can affect these abilities of language control, leading to striking and flagrant linguistic behaviours, such as pathological language mixing (pLM) and pathological switching (pLS). In this paper we report the performance of a Catalan-Spanish bilingual individual (R.R.T.) who, due to a neuroinflammatory disease and subcortical lesions, shows pLS. We tested R.R.T. in several tasks of language production and control, such as picture naming (objects and actions), word translation, blocked naming, and language switching task. R.R.T. was also tested in executive control (EC) tasks, such as task switching and a flanker task. We found several interesting results. First, cross-language intrusions were present much more frequently when R.R.T. was asked to speak in her first (and dominant) language (Catalan) than when she was asked to do so in the nondominant language (Spanish). Second, the results provide evidence suggesting that damage to certain subcortical structures may lead to problems in controlling the language output during verbalization in bilingual speakers. Third, we observed that R.R.T. seemed to show more difficulties in language control with verbs. Fourth, R.R.T. showed impaired performance compared to controls in both task switching and a flanker task. The results are discussed in relation to other findings of pLM and pLS in published single-case reports and in relation to EC deficits.