Lingual Kinematics in Dysarthric and Nondysarthric Speakers with Parkinson's Disease

Articulatory dysfunction is recognised as a major contributor to the speech disturbances seen in Parkinson's disease (PD). The present study aimed to compare lingual kinematics during consonant production within a sentence in eight dysarthric (DPD) and seven nondysarthric (NDPD) speakers with PD with those of eleven nonneurologically impaired normal participants. The tongue tip and tongue back movements of the participants during sentence production were recorded using electromagnetic articulography (EMA). Results showed that both the DPD and NDPD had deviant articulatory movement during consonant production that resulted in longer duration of consonant production. When compared with the NDPD group, the DPD group primarily exhibited increased range of lingual movement and compatible duration of production with an accompanying increase in maximum velocity, maximum acceleration, and maximum deceleration. These findings are contrary to proposed theories that suggest articulatory imprecision in dysarthric speakers with PD is the outcome of reduced range of articulatory movement. 1. Introduction Idiopathic Parkinson’s disease (PD) is a movement disorder typically presenting with motor symptoms such as slowness of movement, muscle rigidity, tremor, and postural instability. Dysarthria, a product of a movement disorder involving the muscles of the speech production mechanism [1], has been frequently identified in individuals with PD, with the majority of the studies reporting an increase of dysarthria prevalence in both numbers and severity with the progress of the disease [2, 3]. Previous studies reported that imprecision of consonant production is the most common articulatory impairment in individuals with PD who suffered a hypokinetic dysarthria [4–9]. Logemann and Fisher [10] reported that stops, affricates, and fricatives were often distorted in their participants with PD. Darley et al. [5–7] hypothesised that the imprecision of consonant production is the result of limited range of movement, muscle rigidity, slowness of movement, and reduced force of movement of the articulators. Thus, direct investigation of articulatory movement, especially tongue movement, during speech production would contribute to the understanding of the nature of articulatory deficits in individuals with PD. To date, a limited number of studies have used electromagnetic articulography (EMA) to investigate the articulatory function in individuals with PD. Ackermann et al. [11] conducted a case study in an akinetic-rigid dysarthric woman with PD using EMA. The authors investigated