Thresholds for formant-frequency discrimination in isolated vowels

Abstract

The threshold of discrimination (or DL) of a shift in formant frequency is thought to be in the range of 3%-6%, based on the oft-replicated results of Flanagan [J. Acoust. Soc. Am. 27, 613-617 (1955)]. This range may not, however, represent the limits of resolution in the auditory system because, for most experiments, subjects were not trained and several pairs of stimuli were presented within trial blocks. In present experiments, thresholds were obtained from well-trained subjects listening to vowels under minimal stimulus uncertainty using an adaptive-tracking paradigm. Thresholds were determined for increments and decrements in F 1 and F 2 for ten synthetic, steady-state vowels modeling a female talker. Results indicated that the DL for both increments and decrements in frequency of the formants increased linearly as a function of frequency, with the exception of 50% higher thresholds where a harmonic fell exactly on the formant frequency. About 80% of the ΔF/F ratios were below 0.02 for formant frequencies greater than 600 Hz. Thus the DL for formant-frequency discrimination appears to be in the range of 1%-2%, or a factor of 3 lower than previous estimates. [Research supported by NIH and AFOSR.]