Subcortical Involvement in Formulaic Language: Studies on Bilingual Individuals With Parkinson's Disease

Purpose An impoverished production of routinized expressions, namely, formulaic language, has been reported for monolingual speakers with Parkinson's disease (PD). Little is known regarding how formulaic expressions might be manifested in individuals with neurological damage who speak more than one language. This study investigated the processing of formulaic language across first language (L1) and second language (L2) in bilingual individuals with PD. Method Eleven Korean-English bilingual speakers with PD, who acquired Korean as L1 and English as L2, were recruited for this study. Two matched control groups composed of 11 healthy Korean-English bilingual individuals and 11 healthy native English speakers were included for comparison. Their performance on three structured tasks (comprehension, completion, and judgment-correction) and conversational speech was measured and compared across groups for analyses. Results The bilingual speakers with PD had significantly impaired comprehension of formulaic language in L1 and had lower proportions of formulaic expressions in their L1 conversational speech compared with the bilingual controls. Regarding L2, both bilingual groups with and without PD were comparable in their English performance across all tasks. Both groups performed significantly poorer in L2 structured tasks than the native English speakers. Spontaneous production of formulaic language in English (L2 for bilingual individuals) was similar across all three groups. Conclusions The results of this study contribute to the growing body of literature on impoverishment of formulaic language production following subcortical dysfunction. Additionally, findings here demonstrate a selective impairment of formulaic language performance in L1 but not L2 for bilinguals with PD, further supporting the role of the basal ganglia in native language.