The effects of foreign accent syndrome on bilingual speech production: Multilevel evidence from a controlled-case study

Foreign Accent Syndrome (FAS) is a rare motor speech disorder with altered speech patterns perceived as a foreign accent. The effects of FAS on the first (L1) and second-acquired (L2) languages in bilinguals have not been examined in depth and knowledge about its neural correlates is limited. Additionally, possible disruptions in auditory-motor feedback processes supporting speech monitoring and voice adaptation are rarely assessed. This study reports on P1, an L1 Catalan- L2 Spanish bilingual with FAS. We sought to characterize FAS in her two languages using a multilevel approach combining perceptual, phonetic, neuropsychological, sensorimotor adaptation to auditory feedback and structural neuroimaging analyses. Results showed that P1's L1 and L2 speech production were perceived as foreign by native bilingual listeners. Phonetic analyses revealed segmental and suprasegmental disturbances in both languages resulting from focal left motor cortex damage. Voice adaptation to auditory noise revealed an abnormal pattern, with differences between L1 and L2, suggesting altered auditory-motor integration. Notably, P1's speech rate, fluency and eloquence were more affected in her L1, suggesting decreased automaticity in this language. She also presented domain-general executive control deficits and increased L1 to L2 switching, as she found L2 production easier. These findings suggest differential effects of FAS on the L1 and L2 speech production of P1, with increased L1-L2 switching as a potential compensatory strategy to decrease executive control burden in L1 production and facilitate more fluent communication. Our findings highlight a potential role for disrupted auditory-motor speech and voice integration in the manifestation of bilingual FAS.