Effect of levels of stimulus uncertainty and consonantal context on formant frequency discrimination.

Abstract

Discrimination thresholds for the second formant of vowels in consonantal context were significantly larger than for vowels in isolation in a report by Mermelstein [J. Acoust. Soc. Am. 63, 572 (1978)]. These results were not upheld in a recent report to this society [Kewley-Port and Watson, J. Acoust. Soc. Am. 89, 1996 (A) (1991)] for testing under minimal stimulus uncertainty procedures. Moreover, Mermelstein’s thresholds were a factor of 5 larger than those reported by Kewley-Port and Watson. The present experiment examines the effects of testing under higher levels of stimulus uncertainty in conditions more similar to those of Mermelstein. For well-trained subjects, most thresholds for the eight CVC stimuli tested did not change when levels changed from minimal to medium uncertainty. Further studies, using testing conditions similar to those of Mermelstein, employed untrained subjects. Results indicated that some subjects rapidly improved their ability to discriminate changes in formant frequency during just 1 h of testing. The differential effects of consonantal context, training, and levels of stimulus uncertainty will be discussed. [Research supported by NIH and AFOSR.]