FUNDAMENTAL-FREQUENCY EFFECTS ON THRESHOLDS FOR VOWEL FORMANT DISCRIMINATION

The present experiments examined the effect of fundamental frequency ( F0) on thresholds for the discrimination of formant frequency for male vowels. Thresholds for formant-frequency discrimination were obtained for six vowels with two fundamental frequencies: normal F0 (126 Hz) a nd low F0 (101 Hz). Four well-trained subjects performed an adaptive t racking task under low stimulus uncertainty. Comparisons between the n ormal-F0 and the low-FO conditions showed that formants were resolved more accurately for low FO. These thresholds for male vowels were comp ared to thresholds for female vowels previously reported by Kewley-Por t and Watson [J. Acoust. Sec. Am. 95, 485-496 (1994)]. Analyses of the three F0 sets demonstrated that formant thresholds were significantly degraded for increases both in formant frequency and in FO. A piece-w ise linear function was fit to each of the three sets of Delta F thres holds as a function of formant frequency. The shape of the three paral lel functions was similar such that Delta F was constant in the Fl reg ion and increased with formant frequency in the F2 region. The capabil ity for humans to discriminate formant frequency may therefore be desc ribed as uniform in the Fl region (<800 Hz) when represented as Delta F and also uniform in the F2 region when represented as a ratio of Del ta F/F. A model of formant discrimination is proposed in which the eff ects of formant frequency are represented by the shape of an underlyin g piece-wise linear function. Increases in F0 significantly degrade ov erall discrimination independently from formant frequency. (C) 1996 Ac oustical Society of America.