Linear phoneme boundaries for German synthetic two-formant vowels.

The phonetic boundaries of variable, synthetic two-formant vowels were studied in psychophysical tests. In the F1 versus F2 formant plane, vowel boundaries appeared to be straight and all but one were parallel to the formant axes. Discrimination of two of the eight German vowels examined relied within certain boundaries upon information of the frequency of the first formant (F1) independent of that of the second (F2) or vice versa. Two vertical F1 boundaries were common to six vowels and one horizontal F2 boundary was common to five vowels. Interpreted in the light of recent neurophysiological data these findings point to the existence of mechanisms of vowel recognition with independent assessment of the two formants.