Acoustic and perceptual comparison of chronic and incipient spastic dysphonia.

Vocal symptoms of patients with chronic and incipient spastic dysphonia were compared on a number of acoustic and perceptual parameters. Patients with incipient spastic dysphonia displayed less severe strain-strangle phonation, effort, rhythm, and stress. Harshness was the only perceptual parameter on which incipient spastic dysphonics were rated higher than chronic spastic dysphonics. Changes in the acoustic measures of laryngealization, harmonic change, mean vowel duration, and duration ratio between stressed and unstressed vowels accompanied changes in listeners' perception of strain-strangle phonation and effort. The variation in acoustic characteristics such as laryngealization and harmonic change as well as normal phonation indicated that both groups were characterized by a variety of phonatory modes.