MODELING FORMANT FREQUENCY DISCRIMINATION OF FEMALE VOWELS

The present investigations were designed to establish the features of vowel spectra that mediate formant frequency discrimination. Threshold s for detecting frequency shifts in the first and second formants of t wo steady-state vowels were initially measured for conditions in which the amplitudes of all harmonics varied in accordance with a model of cascade formant synthesis. In this model, changes in formant frequency produce level variations in components adjacent to the altered forman t as well as in harmonics spectrally remote fro the shifted resonant f requency. Discrimination thresholds determined with the cascade synthe sis procedure were then compared to difference limens (DLs) obtained w hen the number of harmonics exhibiting level changes was limited to th e frequency region surrounding the altered formant. Results indicated that amplitude variations could be restricted to one to three componen ts near the shifted formant before significant increases in formant fr equency DLs were observed. In a second experiment, harmonics remote fr om the shifted formant were removed from the stimuli. In most cases, t hresholds for these reduced-harmonic complexes were not significantly different from those obtained with full-spectrum vowels. Preliminary e valuation of an excitation-pattern model of formant frequency discrimi nation indicated that such a model can provide good accounts of the th resholds obtained in the present experiments once the salient regions of the vowel spectra have been identified. Implications of these findi ngs for understanding the mechanisms mediating vowel perception are di scussed. (C) 1996 Acoustical Society of America.