ASA 125th Meeting Ottawa 1993 May

5pSP1. Modeling format frequency discrimination.

Mitchell S. Sommers

Diane Kewley-Port

Depts. of Psychol. and Speech and Hear. Sci., Indiana Univ., Bloomington, IN 47405

Changes in the formant frequencies of steady-state vowels can produce level changes in harmonic components throughout the bandwidth of the stimulus. To successfully model thresholds of formant frequency discrimination, however, it is necessary to determine whether level changes in components spectrally remote from the altered formant affect discrimination performance. Therefore, the present experiments investigate which harmonics affect performance in order to evaluate excitation-pattern models of formant frequency discrimination. Synthetic tokens of the vowels /u/ and /e/ were generated by digitally summing the first 24 harmonics of a 200-Hz fundamental. Minimal uncertainty thresholds were obtained for F1 increments in /e/ and F2 decrements in /u/ when: (1) all harmonics were allowed to vary; (2) harmonic level variations were restricted to a subset of components spectrally close to the altered formant; and (3) harmonics remote from the shifted formant were excluded from the stimulus. Results indicated that thresholds for conditions (1) and (2) did not differ until level variations were restricted to between two and three components. Thresholds for condition (3) were not significantly different than those obtained for vowels with a full complement of harmonics. Excitation-pattern models of the results will be discussed. [Research supported by NIH.]