Difference limens for synthetic vowel spectra

Abstract

Difference limens (DLs) along synthetic vowel continua were measured as distances in the auditory-perceptual space proposed by J. D. Miller [J. Acoust. Soc. Am. 85, 2114–2134 (1989)]. The continua represent straight lines that lie parallel with one of the axes of the space (x′, y′, and z′). Groups of six continua share a common center value, or reference point. Movement along these continua result in distinct patterns of frequency change for F1, F2, and F3 relative to the reference point formant values. These patterns vary with the direction and axis of movement. Reference points were selected from the interiors of ten vowel zones and seven boundary areas between vowel zones. An adaptive up—down procedure employing a cued, two-alternative, forced-choice (2AFC) task was utilized to estimate the 79.5% correct point along each continuum. Vowel tokens representing the reference points served as the cue stimuli. DLs were estimated twice for each continuum from each of four subjects. In general, the results of this experiment reflect smaller DLs for vowel formant frequencies than have been found in the past and suggest that while an overall average DL for distance in the auditory-perceptual space may be estimated, DLs vary significantly with the axis of movement. Additionally, no significant difference was found between continua associated with vowel centers and vowel boundaries. These results will be compared with similar results estimating DLs for single-formant variation in vowels. [Work supported by NIDCD.]