Perceptual comparisons among a set of vowels similar to /æ/: Some differences between psychophysical distance and phonetic distance

A set of 66 vowels acoustically similar to /ae/ were synthesized by adding together sinusoidal harmonics of the appropriate frequencies, amplitudes, and phases [Carlson, Granstrōm, and Klatt, J. Acoust. Soc. Am. Suppl. 1 65, S6 (1979)]. Subjects were asked to estimate either (1) the psychophysical distance, or (2) the phonetic distance between each stimulus and a reference vowel in a 300‐trial randomized test. Stimulus manipulations included changes to formant frequencies, formant bandwidths, spectral tilt, phase relations among harmonies, vocal tract length, and filtering passband/stopband. Results indicate that when subjects are making phonetic comparisons among the stimuli, they pay far less attention to changes in phase, filtering passband, spectral tilt, and formant bandwidths than when making psychophysical judgements. An acoustically based distance metric consistent with the phonetic data is being sought. [Work supported by an NIH grant.]