A comparison of equal-appearing interval scaling and direct magnitude estimation of nasal voice quality.

Listeners rated the nasality of synthesized vowels using two psychophysical scaling methods (equal-appearing interval scaling and direct magnitude estimation). A curvilinear relationship between equal-appearing interval ratings and direct magnitude estimations of nasality indicated that nasality is a prothetic rather than metathetic dimension. It also was shown that the use of direct magnitude estimation results in nasality ratings that are more consistent and reliable. The results of this experiment are discussed in relation to other studies that have examined the validity and reliability of equal-appearing interval scaling of voice quality. Additionally, there is a discussion of methodological issues for future research and the implications of the findings for clinical and research purposes.