Discrimination of Vowel Spectrum in Sensorineural Hearing Impairment

Abstract

Measurements are reported comparing normal and impaired auditory discrimination for formant frequencies of synthetic vowels. Vowel spectra were shaped by two formant resonators with controllable center frequencies, F1 and F2. For discrimination measurements three vowels were presented on each trial. For two of the vowels, F1 and F2 were held constant. For the third vowel, F2 was set at a higher frequency. The task of the listener was to tell which one of the vowels was different from the other two. A programmer controlled the synthesizer so as to present a sequence of trials with downward adjustment of amount of F2 difference after each correct response and upward adjustment after each wrong response. Thus, over a sequence of trials the amount of F2 difference typically decreased from above the difference limen until oscillatory adjustments occurred above and below the limen. Results: frequency position and relative amplitude of F1 has a marked effect of the F2 discrimination limen. All groups show good F2 discrimination when the formants are separated by more than 1 oct. Some subjects demonstrated abnormally poor discrimination when F2 was 10 dB lower than F1, but improved when the amplitude difference was reduced. [Work supported by U. S. Public Health Service grant.]