On explaining certain male-female differences in the phonetic realization of vowel categories

The scaling between female and male formant frequencies tends to be highly nonuniform across vowel categories with the result that female vowels exhibit greater between-category dispersion in the F-1 x F-2 plane than male vowels. Vocal tract modeling studies strongly suggest that this greater dispersion of female vowels is partly behavioral, rather than purely anatomical, in origin. The present study tested one explanation for this behavioral difference between females and males, viz., that without the compensatory effect of greater dispersion, the typically higher fundamental frequency (f(0)) of female talkers would yield reduced identifiability of vowels because of sparser harmonic sampling of spectral envelopes. The specific question addressed was whether, all else being equal, a higher f(0) has the assumed deleterious effect on vowel identifiability. In two experiments, the overall effect of increasing f(0) beyond 150 Hz was to reduce vowel labeling accuracy. Across individual vowel categories, the effect of raising f(0) varied. Auditory modeling suggests that this category variation is partly attributable to differing degrees to which a high f(0) obscured the distinctive auditory properties of each vowel category. Consistent with the spectral undersampling account, the performance decline at high f(0)s was reduced or eliminated when f(0) was time-varying rather than constant. (C) 1996 Academic Press Limited