Generalization in the vowel space

Abstract

Vowels may be represented by a three-dimensional volume of space. The axes of the volume may be defined in articulatory terms (front–back, high–low, rounded–unrounded) or in physical terms (F1, F2, F3). Shepard [Science 237, 1317–1323 (1987)] plotted data of Peterson and Barney [ 175–184 (1952)] to show that generalization in the vowel space is an instance of his universal law of generalization, an exponential decay function with physical measures on the x axis. This theory is contradicted by the magnet effect [P. Kuhl, Percept. Psychophys. 50, 93–107 (1991)] which indicates that some areas of the vowel space are perceptually shrunken. Experiments with naive adult subjects were executed. Generalization, ABX, and discrimination experiments were performed using eight cardinal vowels plus intermediate steps between selected vowels. Results, indicating both Shepard and Kuhl are partially correct, are best represented by Gluck’s scheme [Psych. Sci. 2, 50–55 (1991)] with the data indicating that it is the distinctive features of vowels that are perceived categorically. There was little evidence of language-specific effects for adults. Pilot work with newborns indicate that they organize the vowel space like adults.