Degree of articulatory constraint predicts locus equation slope for /p,t,s,∫/

Abstract

The degree of articulatory constraints (DAC) model (Recasens, Pallarès, & Fontdevila, 1997) proposes that consonants involving the movement of the tongue dorsum are more resistant to coarticulation than those with a more fronted articulation. We assessed this claim using locus equation (LE) slopes as indicators of coarticulation. Participants were asked to produce V1(t).CV2 sequences as part of two-word phrases in a scripted dialog, where C is one of /p, t, s, ʃ/. LE were derived by measuring F2 at V2 onset and midpoint. Since LE slopes approaching 1 indicate high levels of coarticulation, it was hypothesized that segments with the lowest DAC would have the steepest slopes (/p/>/t/>/s/>/ʃ/) and this is what we found, lending support to the DAC model. A secondary hypothesis assessed the effect of emphatically stressing C on the LE. Participants partook in a dialog involving a “mishearing” of either the target C (Prominent condition) or the preceding V1(t) (Control condition), and they repeated the two word sequence. We expected participants to emphasize the misheard segment and reduce coarticulation if the C was misheard (lower LE slope). Our findings indicate that only the LE slopes of sibilants /s/ and /ʃ/ were reduced under prominence, perhaps due to their high DAC values.