Perception of vowel height: the role of F1-F0 distance.

Perceived vowel height has been reported to vary inversely with the distance (in Bark) between the first formant frequency (F1) and the fundamental frequency (F0) [H. Traunmüller, J. Acoust. Soc. Am. 69, 1465-1475 (1981)]. Syrdal and Gopal [J. Acoust. Soc. Am. 79, 1086-1100 (1986)] observed that naturally produced [+high] and [-high] vowels tend to divide at a critical F1-F0 distance of 3-3.5 Bark, corresponding to the bandwidth of the "center of gravity" effect [L. Chistovich and V. Lublinskaja, Hear. Res. 1, 185-195 (1979)]. In the present study, listeners identified three sets of synthetic vowels varying orthogonally in F1 and F0 and ranging from /i/-/I/, /I/-/epsilon/, and /epsilon/-/ae/. For the /I/-/epsilon/ set, which corresponds to the [+high]/[-high] distinction, there was a relatively sharp identification boundary located at an F1-F0 distance of 3-3.5 Bark. However, for the /epsilon/-/ae/ and /i/-/I/ sets, which occupied regions where the F1-F0 distance was always greater than or always less than 3 Bark, vowel labeling varied more gradually as a function of F1-F0 distance. Also, F1-F0 distance was a better predictor of labeling performance than F1 alone only for the /I/-/epsilon/ set. Possible sources of the F1-F0 distance cue for vowel height are discussed.