The perceptual relevance of changes to glottal-pulse parameters is studied. First, it is demonstrated that a distance measure based on excitation patterns can predict audibility discrimination thresholds for small changes to the R parameters of the Liljencrants-Fant (LF) model. Next, by using this measure the perceptual relevance of the LF parameters is quantified. Results are presented for a number of sets of glottal-pulse parameters that were taken from literature, representing distinct voice qualities.