Searching for an auditory description of vowel categories

This paper examines three auditory hypotheses concerning the location of category boundaries among vowel sounds. The first hypothesis claims that category boundaries tend to occur in a region corresponding to a 3-Bark separation between adjacent spectral peaks. According to the second hypothesis, vowel category boundaries are determined by the combined effects of the Bark distances between adjacent spectral peaks but that the weight of each of these effects is inversely related to the individual sizes of the Bark distances. In a series of perceptual experiments, each of these hypotheses was found to account for some category boundaries in American English but not others. The third hypothesis, which has received preliminary support from studies in our laboratory and elsewhere, claims that listeners partition the vowel space of individual talkers along lines corresponding to relatively simple linear functions of formant values when scaled in auditorily motivated units of frequency such as Bark.