Application of pitch perturbation measures to the assessment of hoarseness in Parkinson's disease

To determine whether measures of pitch perturbation relate to the occurrence of hoarseness in a neurological disease, patients with Parkinson's disease (hypokinesia) and normal aging controls were recorded. Pitch period lengths were measured from recordings of extended vowel productions to compute: mean adjacent differences; mean deviations of cycles from predicted values based on adjacent cycles; and jitter ratios. Three trained judges rated hoarseness on a seven‐point scale from the same recordings. Mean adjacent differences were linearly related to fundamental frequency in hypokinesia but not in normal speech. Judgements of hoarseness were significantly related to mean adjacent differences, mean deviations and jitter ratios in the hypokinetic speakers. No significant relationships between hoarseness and the perturbation measures were found in the aging controls. Judgements of hoarseness did not accurately discriminate between normal and hypokinetic speakers, while the mean adjacent differences and devi...