The perceptual relevance of locus equations

Identification curves were estimated for the English consonants /b,d,g/ using five-formant CV synthetic stimuli comprehensively sampling the F2 onset-F2 vowel acoustic space in the vicinity of /b,d,g/ locus equations [H. Sussman et al., J. Acoust. Soc. Am. 90, 1309-1325 (1991)]. The stimuli included 10 English monophthongal vowel contexts, 11 levels of F2 onset per vowel, and 3 levels of F3 onset orthogonally varied with the F2 variables (10 vowels x 11 F2 onsets x 3 F3 onsets = 330 stimuli). After brief training, each of six subjects, three male and three female, was presented eight trials of each of the stimuli, one or two trials per day over a period of several days. Systems of identification curves were visualized as identification surfaces situated in locus equation acoustic space and were overlaid with acoustic data from five male speakers in order to judge the degree of correspondence between perception and acoustic data. A chi square analysis was also performed in order to quantify the correspondence between the observed perception data and expected frequencies derived from the acoustic data. The results, when interpreted in terms of a dominance hierarchy hypothesis, strongly indicate F2 onset and F2 vowel, in combination, serve as important cues for stop consonant place of articulation.