Changes of rhythm of vocal fundamental frequency in sensorineural hearing loss and in Parkinson's disease

The neurological control of speech is a complex process that involves phonation organs, respiratory and auditory systems. In the instance of a steady-as-possible sustained phonation, the vocal fundamental frequency (F ₀ ) is rhythmic and oscillating in varied degree. The present study examines the changes in the rhythm of F ₀ in subjects with sensorineural hearing loss (SNHL) as well as in subjects with Parkinson's disease (PD) after being orally administered with dopamine. The sustained steady vocalizations of vowel [a:] from 19 subjects with SNHL and from 13 subjects with normal hearing were collected and statistically compared. In addition, the phonations of 14 subjects with PD before and after oral medication with oral dopamine were collected and statistically compared. The F ₀ of a phonation was retrieved by digital signal processing of voice signals, and were then analyzed using Fourier transformation to acquire the amplitude of oscillation at different frequency components. Our study showed that subjects with SNHL had significantly larger fluctuation in the low frequency (< 3 Hz) than the subjects with normal hearing. In addition, dopamine medication significantly reduced the fluctuation in the midfrequency (3-8 Hz) in subjects with PD. Our study indicates that power spectral analysis of F ₀ may potentially be very useful in the evaluation or detection of SNHL and PD. The rhythms of F ₀ are produced from neurological controls of phonation and may be used to access clinical diseases by a sustained phonation.