Progression of Voice and Speech Impairment in the Course of Parkinson's Disease: A Longitudinal Study
Table 3
Abbreviations and definitions of the speech parameters.
Speech modality
Parameter
Definition
Voice
Jitter (measure of microperturbations of frequency)
Average absolute difference between consecutive differences between consecutive periods, divided by the average period
Shimmer (measure of microperturbations of amplitude)
Average absolute difference between consecutive differences between the amplitude of consecutive periods
Noise to harmonics ratio (nhR)
Automatic comparison of harmonic (periodically recurring) and inharmonic sound fractions
Mean
Average fundamental frequency calculated for the entire reading task
Articulation
Vowel articulation index (VAI)
Comprehensive measure of the “working space” for vowels based upon the extraction of formant frequencies of defined vowels of the reading task according to the formula; VAI = () / ()
Percentage of pauses within polysyllabic words (Pinw%)
Percentage of pauses within polysyllabic words of total speech pauses (periods of silence < 10 ms)
Tempo/fluency
Net speech rate (NSR)
Net production of syllables per second based upon the reading task
Pause ratio (PR%)
Percentage of pause rate based upon the reading task
Prosody
SD
Standard deviation of fundamental frequencies calculated for the reading task as a measure of pitch variability