Effect of linguistic context on the perception of consonants in Parkinsonian Read French speech.

We examined the effect of linguistic factors on the perceptual identification of intervocalic consonants produced by speakers with Parkinson's Diseases (PD). To neutralize the effect of preceding and following contexts, all the intervocalic consonants were excised with half the preceding and following vowels. We recorded 10 PD and 10 healthy speakers reading a text. An average of 114 VCV sequences per speaker was obtained. In total, our corpus consisted of 2280 stimuli. For the perception test, 20 adults native speakers of French were instructed that they would be presented utterances produced by different speakers and that they were to identify the sequences and write what they heard. No information was given on the sequence type (VCV). The reported consonant was examined in relation to the intended consonant; the score of distorsion was the number of phonetic features differing from the prototypical consonant. The results were examined as a function of the following/or preceding linguistic factors: consonant nature, oral/nasal vocalic context, class of word (function or content) and prosodic position within sentences. Consonant imprecision was confirmed in the speech of PD speakers. Two groups of patients were observed: the former with a low degree of dysarthria severity and scores of consonant identification close to that of healthy speakers; the latter with a high degree of dysarthria severity and a low identification score. Linguistic factors were shown to affect consonant production and perception. In both normal and PD speech, consonants had more features identified when they belonged to content words, word-initial syllables or final-phrase syllables. This suggests that in Parkinson's disease speech disorders relate to motor control and not to a loss of the linguistic knowledge.