Vocal tract control in Parkinson's disease: phonetic feature analysis of misarticulations

Consonant articulation patterns of 200 Parkinson patients were defined by two expert listeners from high fidelity tape recordings of the sentence version of the Fisher-Logemann Test of Articulation Competence (1971). Phonetic transcription and phonetic feature analysis were the methodologies used. Of the 200 patients, 90 (45%) exhibited some misarticulations. Phonetic data on these 90 dysarthric Parkinson patients revealed articulatory errors highly consistent in detailed production characteristics. Manner changes predominated. Phoneme classes that were most affected were the stop-plosives, affricates, and fricatives. In terms of perception features (Chomsky & Halle, 1968), the stop-plosives and affricates, which are normally [-continuant] were produced as [+continuant] fricatives; fricatives that are [+strident] were produced as [-strident]. There is no implication, however, that Parkinsonism involves a perception deficit. Analysis of the articulatory deficit reveals inadequate tongue elevation to achieve complete closure on stop-plosives and affricates, which can be expressed in production features as a change from [+stop] to [+fricative]. There was also inadequate close constriction of the airway in lingual fricatives, which in articulatory features can be expressed as a change from [+fricative] to [-fricative]. Both the incomplete contact for stops and the partial constriction for fricatives represent an inadequate narrowing of the vocal tract at the point of articulation. These results are discussed in relation to recent EMG studies and other physiologic examinations of Parkinsonian dysarthria.