Locus equations in the light of articulatory modeling

This paper examines the significance of the so-called “locus equation” by means of articulatory simulations of V1CV2 utterances with different intergestural timing, and, therefore, with varying degrees of consonant–vowel coarticulation. Movement toward the vowel V2 started (i) at the beginning of the transition to the consonant, (ii) at the beginning of the complete consonant closure, or (iii) at the beginning of the release of the consonant. For each combination of vowels and each consonant, F2 onset of V2 as a function of F2 of V2 was adequately described by straight lines corresponding to locus equations (referred to as first-order locus equations). The findings show that the derived locus equations depend on the consonant place on the one hand and on the degree of coarticulation on the other. The effect of varying intergestural timing was compared with published data on locus equation coefficients for individual speakers using the format of y-intercept plotted versus slope for each place of articulation (referred to as a second-order locus equation). These comparisons demonstrate that the model adequately captures the natural place-dependent variations in slope and intercept. Also it provides accurate numerical matches with their speaker-specific ranges suggesting the hypothesis that the variability derives, to a significant extent, from individual differences in intergestural timing.