Locus equation encoding of stop place: revisiting the voicing/VOT issue

This study explored the consistency of locus equation slopes to serve as phonetic descriptors of stop place in CV utterances across voiced versus voiceless aspirated stops. Using traditional locus equation measurement sites for F2 onsets, voiceless labial and coronal stops had lower locus equation slopes relative to their voiced counterparts, whereas velars failed to show voicing differences. When locus equations were derived using F2 onsets for voiced stops that were measured closer to the stop release burst, comparable to the protocol for measuring voiceless aspirated stops, the slope differences across voicing were greatly minimized. This methodological factor, rather than an underlying phonetic-based explanation, provides a reasonable account for the observed flatter locus equation slopes of voiceless labial and coronal stops relative to voiced cognates.