Interarticulator phasing and locus equations

A locus equation plots the frequency of the second formant at vowel onset against the target frequency of the same formant for the vowel in a consonant–vowel sequence. The slope of the equation has been assumed to reflect the degree of coarticulation between the consonant and the vowel, with higher slopes associated with more coarticulation. This study examined the articulatory basis for this assumption, using VCV sequences where the consonant was a bilabial stop /p, b/ and the vowels one of /i, a, u/. Articulatory movements were recorded using a magnetometer system. Four subjects participated and produced ten repetitions of each sequence. One articulatory measure was the temporal phasing between the onset of the lip closing movement and the onset of the tongue body movement from the first to the second vowel. Another was the magnitude of the tongue movement from the onset of the second vowel to the tongue position for the vowel, averaged across four receivers placed on the tongue. When compared with the corresponding locus equation slopes, neither measure showed support for the assumption that the slope serves as an index of the degree of coarticulation between the consonant and the vowel. [Work supported by NIH.]