Examining Narrative Language in Early Stage Parkinson's Disease and Intermediate Farsi-English Bilingual Speakers

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This study aimed to examine procedural aspects of language (grammaticality, syntactic complexity, regular past tense verb production), verb use, and the association between motor-speech, language abilities, and intelligibility in Early Stage Parkinson's Disease (PD) and Intermediate Farsi-English Bilingual Speakers (L2). Ullman’s Declarative-Procedural Model (2001) provided this study with a dual-mechanism model that justified a theoretical comparison between these two populations. Twenty-four neurologically healthy native speakers of English, twenty-three Parkinson’s Disease participants, and thirteen bilingual Farsi-English speakers completed three narrative picture description tasks and read the first three sentences of the Rainbow Passage. Language samples were transcribed and analyzed to derive measures of morphosyntax and verb use, including grammatical accuracy, grammatical complexity, and proportions of regular past tense, action verbs and light verbs. The results did not show any evidence of morphosyntactic or action verb deficit in PD. Neither was there any evidence of a trade-off between morphosyntactic performance and severity of speech motor impairment in PD. L2 speakers had lower scores on grammatical accuracy and a measure of morphosyntactic complexity, but did not differ from monolingual speakers on measures of verb use. Overall, these results show that language abilities (morphosyntax and verb use) are preserved in early stage PD. This study replicates the well-documented finding that morphosyntax is particularly challenging for late bilingual speakers. The results did not support Ullman’s Declarative-Procedural (2001) hypothesis of language production in Parkinson’s Disease or L2 speakers.