Thresholds for formant-frequency discrimination of vowels in consonantal context.

Thresholds for formant frequency discrimination were shown to be in the range of 1%-2% by Kewley-Port and Watson [J. Acoust. Soc. Am. 95, 485-496 (1994)]. The present experiment extends that study and one by Mermelstein [J. Acoust. Soc. Am. 63, 572-580 (1978)] to determine the effect of consonantal context on the discrimination of formant frequency. Thresholds for formant frequency were measured under minimal stimulus uncertainty for the vowel /I/ synthesized in isolation and in CVC syllables with the consonants /b/, /d/, /g/, /z/, /m/, and /l/. Overall, the effects of consonantal context were similar to those reported by Mermelstein (1978), although his threshold estimates were a factor of 4-5 times larger because less-than-optimal psychophysical methods had been used. Compared to the vowel in isolation, consonantal context had little effect on thresholds for F1 and a larger effect on F2. When a shift in threshold was observed, subject variability was high and resolution was degraded by as much as a factor of 2. Analyses of stimulus parameters indicated that resolution was degraded by shortening steady-state vowel duration or if the separation between the onsets of the formant transitions was small. Overall, consonantal context makes it more difficult for some, but not all, listeners to resolve formant frequency as accurately as for vowels in isolation.