Prosodic characteristics of Parkinsonian speech: the effect of levodopa-based medication

Individuals with Parkinson disease (PD) typically experience fluctuations in motor performance after years of treatment with the medication levodopa. The purpose of this study was to provide an acoustic profile of prosodic characteristics of speech produced by individuals with PD across treatment-related fluctuations. Specifically, data were collected in three conditions: before morning medication, 1 hour after morning medication, and 2 hours after medication. Nine individuals with PD participated in this study. Compared to age-matched controls, the participants demonstrated increased percent pause times, decreased speech rate, and decreased standard deviation of fundamental frequency, but no differences were found in articulation rate. After taking medication, few changes were noted, although descriptive analysis revealed improvements in percent pause time that continued for the first 2 hours after taking medication. The current results support the conclusion that patients with PD demonstrate speech prosody deficits that are alleviated in some individuals after the administration of levodopa-based medication.

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Idiopathic Parkinson disease (PD) is a progressive neurological disease characterized by death of dopaminergic neurons primarily in the substantia nigra pars compacta, but also in other areas of the brain (Bhatnagar & Andy, 1995; Brodal, 1998; Lang & Lozano, 1998a). Typical motor symptoms of PD include muscle rigidity, akinesia (difficulty initiating movement), bradykinesia (slow movement), and rest tremor (Brodal, 1998). The speech disorder occurring as a result of PD can be considered a form of hypokinetic dysarthria, and perceptual characteristics of hypokinetic dysarthria include monopitch, reduced stress, monoloudness, and inappropriate silences (Darley, Aronson, & Brown, 1969a, b). This indicates that individuals with PD typically exhibit deficits in speech prosody (i.e., variations of intensity, frequency, and timing). The following review includes acoustic examinations of prosody in speakers with PD who are unmedicated or off medication (i.e., OFF state), followed by reports of prosodic characteristics of PD accompanying initiation of levodopa treatment and accompanying levodopa-related fluctuations (ON vs. OFF state).

PROSODY IN INDIVIDUALS WITH PD

Individuals with PD have been shown to demonstrate reduced fundamental frequency ([F.sub.o]) range and variability during speaking tasks (Canter, 1963, 1965; Flint, Black, Campbell-Taylor, Gailey, & Levinton, 1992; Metter & Hanson, 1986). Canter (1963, 1965) noted decreased [F.sub.o] range during syllable production, and a number of researchers have found decreased [F.sub.o] range/variability during reading (Canter, 1963; Flint et al., 1992; Metter & Hanson, 1986). Although normal speakers typically demonstrate a high [F.sub.o] range and variability during speaking tasks (Canter, 1963), the decrease in [F.sub.o] variation in individuals with PD may reflect a prosodic deficit, corresponding to the perceptual feature of monotone speech (Canter, 1963). In addition to decreased [F.sub.o] variability, individuals with PD demonstrate decreased use of [F.sub.o] changes to mark the difference between questions and statements (Le Dorze, Ouellet, & Ryalls, 1994; Le Dorze, Ryalls, Brassard, Boulanger, & Ratte, 1998; Torp & Hammen, 2000).

Rate of speech has also been shown to be impaired in PD speech. Parkinsonian speech rate has been characterized as either accelerated or comparable compared to normal controls. Ackermann, Konczak, and Hertrich (1997) hypothesized that impaired self-timing for motor movements...