A cross-linguistic investigation of locus equations as a phonetic descriptor for place of articulation.

A previous study [H. Sussman, H. McCaffrey, and S. Matthews, J. Acoust. Soc. Am. 90, 1309-1325 (1991)] of American English CV coarticulation showed a remarkably linear relationship between onset frequencies of F2 transitions, plotted on the y axis, in relation to the F2 midvowel "target" frequencies, plotted on the x axis, for CVC tokens with initial [b d g] and ten medial vowel contexts. Slope and y-intercept values of regression functions fit to these scatterplots ("locus equations") were shown to serve as statistically powerful phonetic descriptors of place of articulation. The present study extends the locus equation metric to three additional languages--Thai, Cairene Arabic, and Urdu--having both two and four place contrasts for syllable-initial voiced stops. A total of 14 speakers (Thai = 6, Arabic = 3, Urdu = 5) produced 1740 CVC tokens that were acoustically analyzed using MacSpeech Lab II. Strong linear regression relationships were found for every stop category across all speakers. Slopes and y intercepts systemically varied as a function of place of articulation. Cross-language comparisons of stop place categories were performed but variability of slope and y intercept means tempered conclusions concerning the existence of CV "phonetic hot spots."