Research Article

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 modalityParameterDefinition

VoiceJitter (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

ArticulationVowel 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/fluencyNet 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  SDStandard deviation of fundamental frequencies calculated for the reading task as a measure of pitch variability