Vowel posture normalization.

A simple normalization procedure was applied to point-parametrized articulatory data to yield quantitative speaker-general descriptions of "average" vowel postures. Articulatory data from 20 English and 8 Japanese speakers, drawn from existing x-ray microbeam database corpora, were included in the analysis. The purpose of the normalization procedure was to minimize the effects of differences in vocal tract size and shape on average postures derived from the raw data. The procedure resulted in a general reduction of cross-speaker variance in the y dimension of the normalized space, within both language groups. This result can be traced to a systematic source of variance in the y dimension of the raw data (i.e., palatal height) "successfully removed" from the normalized data. The procedure did not result in a comparable, general reduction in cross-speaker variance in the x dimension. This negative result can be traced partly to the new observation that some speakers within the English sample habitually placed their tongues in a fronted position for all vowels, whereas other speakers habitually placed their tongues in a rearward position. Methods for evaluating articulatory normalization schemes, and possible sources of interspeaker variability in vowel postures, are discussed.