On the relation of apparent naturalness to phonetic perceptual identification of vowels

Abstract

A set of synthetic test syllables was created varying the attributes of naturalness and phonetic vowel height and advancement. These acoustic items were used in tests calibrating the relation of naturalness to phonetic perceptual resolution. Two acoustic methods were used to create naturalness variants: (1) variation in the excitation of the synthetic voicing source and (2) variation in the bandwidth of the formant centers. A naturalness tournament was composed of items drawn from the test series, and the sensitivity of perceivers to the vowel contrast was estimated with the cumulative d′ across the series in identification tests. These outcomes reveal different effects of each acoustic manipulation: an independence of the outcome of the naturalness tournament and the measures of phonetic sensitivity in one case and a close relation between naturalness and phonetic resolution in the other. Together, the findings show that intelligibility and naturalness can be either orthogonal or contingent aspects of speech perception. These measures offer a tool to understand rule-based and exemplar-based components of phonetic perception. [Research supported by NIH (DC00308).]