Speech-Related Sensory Impairment in Parkinson’s Disease

Abstract

Background. Persons with Parkinson’s disease (PD) show speech impairments that are not solely accounted for by motor impairment. In the literature on motor control of trunk and limbs in PD, somatosensory deficits were found and suggested to be associated with movement abnormalities. Less is known about speech-related sensory systems in PD, and little has been done to investigate the link between specific speech sounds and relevant sensory impairments in PD. Purpose. The primary goal of this dissertation is to determine whether there is a relationship between the speech of persons with PD and their auditory and tactile acuity. Using production of sibilants /s/ and /ʃ/ as the speech target, the study seeks to answer four questions: 1) Do persons with PD produce a smaller acoustic difference between sibilant fricatives relative to healthy controls? 2) Do persons with PD show decreased auditory acuity in discriminating spectral shapes? 3) Do persons with PD show decreased acuity to tactile stimuli on the tongue tip? And 4) Are there relationships of sibilant contrast to auditory and lingual-tactile acuity? Method. Ten participants with PD and ten age- and gender-matched healthy participants were studied. Participants performed three tasks. In the production task, they read a passage and eight sentences with /s/- and /ʃ/-initial words; acoustic contrast between the two sibilants was measured using difference between the average first spectral moments of /s/ and /ʃ/. For the auditory task, in each trial they listened to three aperiodic sounds, acoustically modified from /s/ and /ʃ/ and differing in spectral shapes, and judged which sound was different than the other two; auditory acuity measures were calculated from the psychoacoustic functions of their responses. For the tactile task, they judged the orientation of a dome-shaped grating probe gently touching their tongue tip; tactile acuity measures were extracted from the psychophysical functions of their responses. Group comparisons were made for every measure and correlation analyses were done between the speech-production measures and sensory acuity measures. Results. Results found that participants with PD had a smaller sibilant contrast than healthy controls for productions in sentences, but not for ones in the continuous speech passage. The PD participants had significantly reduced auditory acuity in discriminating spectral shapes relative to healthy controls, and significantly reduced tactile acuity of the tongue tip. Correlation analyses showed significant correlation between the tactile acuity and sibilant contrast for the PD group. Conclusions. Results from the study suggest associations of sensory impairment to speech production in persons with PD, calling for more research into the sensory underpinnings of the speech problems of this clinical population.