This paper compares the effects of acoustic perturbations on perceptual judgments of voice quality in disordered and synthesized vowels. Five levels of jitter, shimmer, and glottal noise, respectively, were systematically added to synthesized vowels. Perceptual judgments of breathiness, hoarseness and harshness showed that glottal noise was correlated more strongly with perceptual judgments of Breathiness and Hoarseness than with Harshness; and was a better predictor of all three perceptual dimensions that were jitter and shimmer.