Evaluation of vowel duration as a cue for the voicing distinction in the following word-final consonant.

Previous measurements have indicated that vowels before voiced and voiceless consonants exhibit a systematic duration difference, the former being longer approximately by a 3:2 ratio than the latter. Experiments with synthetic speech have shown that vowel duration is an important cue for the voicing distinction of the following consonant in word-final position. In the present paper the role of this cue is evaluated for natural speech, which may also contain secondary cues for maintaining this distinction. The stimuli, spoken by a female speaker, were 24 English monosyllabic words ending with voiced stops, fricatives, and consonant clusters after intrinsically long and intrinsically short vowels. Duration of the vowel nucleus was systematically reduced using a digital gating technique. Recognition rates as a function of vowel duration were obtained. Category change takes place mainly for intrinsically long vowels and for high vowels in combination with final fricatives alone or in consonant clusters. In other cases, category change cannot be established even after the vowel duration is reduced to only 30% of its original duration. In particular, the presence of a long voice bar for a final voiced stop will make shortening of the vowel perceptually less effective. A multiple regression analysis of the experimental data indicates that in natural speech not only vowel duration, but also voice bar duration, duration of silent closure preceding the final release transient, and duration of the release burst or frication noise, depending on the consonant type, vary in weight as cues for voicing under different vowel- and consonant-type conditions.