Speech production in Parkinson's disease

Most individuals with PD develop difficulties with their speech production. It is unclear what underlying factors contribute to these speech deficits. One hypothesis is PD talkers are unable to process sensory feedback from the speech musculature in a normal way, which causes their speech to break down (as the speech system relies on sensory information from the articulators to guide its movement). Additionally, PD talkers may have problems coordinating their speech articulators for sound production (i.e., 'motor equivalence'), thereby disrupting speech. In Experiment 1, deficits with sensory feedback and motor equivalence are studied in ten PD and NC (normal control) talkers by observing how these individuals compensate for a perturbing bite block. Subjects produce the vowels /i/ and /u/ separately under three bite block conditions (no bite block/small bite block/large bite block). Problems with sensory feedback are indexed by estimating formant frequencies (F 1 and F2) at the vowel midpoint. Deficits with motor equivalence are addressed by estimating formant frequencies at the vowel onset. Results indicate both talker groups make similar compensatory adjustments with a bite block for both vowels. These findings suggest sensory feedback and motor equivalence are preserved in the speech system of PD talkers.;Experiment 2 investigates differences in PD talkers' production of stop and glide consonants. Stops produced by PD talkers' are imprecise, while the production of glides remains intact. To produce a stop, the speech articulators are required to make rapid movements. In contrast, the articulators move more gradually when producing a glide. Given that PD is associated with slow movement execution (i.e., bradykinesia), one hypothesis is that bradykinesia prevents PD talkers from making rapid articulatory movement required for stop consonant production. To address this issue, PD and NC talkers produced /ba/ and /wa/ during three speech rates (fast/normal/slow). Duration and formant frequency measures were estimated. It was hypothesized that stops would be impaired across all speaking conditions while glides would be altered in the fast speaking condition only. The findings suggested no evidence for bradykinesia in PD talkers' production of stop and glide consonants. Instead, PD talkers showed a deficit in adjusting the syllable transition duration of glides across speaking rates.