Articulatory consequences of Parkinson's disease: perspectives from two modalities.

Language production involves complex yet productively varying motor behavior. Rule-governed combinations yield a finite set of formational units combined in an infinite number of ways. The creativity of language ensures that no particular articulation will be highly automatized. Linguistic articulation is highly complex and varied. As such, it differs from the other more automatized motor behaviors typically studied such as learned movements in apraxia studies or repetitive behavior as occurs in walking or other everyday activities. Language also strives to maintain a balance between ease of articulation and ease of perception, while maintaining linguistically relevant distinctions. We report here a number of studies on the articulatory consequences of Parkinson's disease (PD) in the spoken and signed modalities. Our goal is to highlight the commonalities and distinctions between the two modalities of speech and sign that will allow us to better understand the impingements of PD on language production in general.