The Effects of Levodopa on Speech Timing in Patients with Idiopathic Parkinson's Disease: A Comparison Between DDK and Speech Rate Measures

Michelle Troche, M.A.
Doctoral Student
Department of Communication Sciences and Disorders
University of Florida
Research Speech-Language Pathologist
Malcom Randall Veterans Affairs Medical Center
Gainesville, Fl.

Christine Sapienza, Ph. D.
Professor and Chair
Department of Communication Sciences and Disorders
University of Florida

Overview:

Parkinson's disease (PD) is a neurologic condition characterized by impairment of the basal ganglia with death of dopaminergic neurons primarily in the substantia nigra pars compacta (Brodal, 1998; Kent, Kent, Duffy, & Weismer, 1998; Lang & Lozano, 1998). Typical physical symptoms include muscle rigidity, akinesia, hypokinesia, bradykinesia and resting tremor (Brodal, 1998; Hoehn & Yahr, 1967; Marsden, 1989). Although these cardinal symptoms are commonly reported in the literature, the motor performance of individuals with PD, particularly limb movements and speech articulation, can be relatively normal under certain emergency or experimental conditions (England & Schwab, 1959; Hallett & Khosbin, 1980; McDowell, Lee, & Sweet, 1986), but may deteriorate as tasks become longer and more complex (Benecke, Rothwell, Dick, Day, & Marsden, 1987; Hallett & Khosbin, 1980; Marsden, 1984; Sanes, 1985).

Introduction:

Speech is a complex task involving higher cognitive-linguistic processing and requires the sequential and parallel control of multiple articulators in a highly refined and specific manner. The speech changes evident in PD are termed hypokinetic dysarthria, and are typified by motor deficits in the orofacial musculature and other motor processing problems. The effects of PD are not homogeneous.

Many domains of speech are affected in hypokinetic dysarthria, including respiration, phonation, articulation, resonance and prosody (including speech timing, see Darley, Aronson, & Brown, 1969a; 1969b), creating speech symptoms such as slurring, monopitch voice, reduced stress, monoloudness, imprecise consonant production, variable speech rate, inappropriate pauses, short rushes of speech, and a harsh, breathy voice, among others (Darley, et al., 1969a,b; Canter, 1963, 1965a,b).

Some measures of speech timing focus on speaking rate and determining segmental durations within reading or conversational tasks. Diadochokinetic (DDK) tasks are used specifically to examine articulatory precision, as well as the ability to rapidly alternate articulators between segments. With regard to speech timing, people with PD show significant variability in motor performance among and within speech tasks (Boshes, 1966; Canter, 1963; Metter & Hanson, 1986). Some patients with PD produce normal or accelerated speech tempos with regard to segment durations and DDK (Ackermann & Ziegler, 1991; Canter, 1963; Hammen & Yorkston, 1996; Netsell, Daniel, & Celesia, 1975; Weismer, 1984; Weismer, Jeng, Laures, Kent, & Kent, 2001) while others exhibit decreased rates (Ludlow, Connor, & Bassich, 1987; Metter & Hanson, 1986). Presumably, this intra and inter-task variability is due to differences in the neurophysiological mechanisms responsible for their motor execution (Connor & Abbs, 1991).