Structure and duration of vowels together specify fricative voicing

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Abstract
The durations of vowels specify several types of linguistic information in [humans]. Thus, multiple durational cues may be decoded from the same temporal interval of the signal, a situation which should create perceptual ambiguity. Four perceptual studies of postvocalic fricative voicing examined how information in the duration and dynamic structure of the vowel might combine to resolve these ambiguities. Stimuli were made by varying the duration and structure of vowels from utterances of /jus/ and /juz/. In the 1st experiment vowel structure differences influenced voicing judgments by 30-40%. The 2nd experiment showed that the offset characteristics of the /juz/ vowel were not the major vowel structure cues in the 1st experiment. The 3rd experiment examined identification and discrimination of stimuli with neutral vocalic voicing cues which differed only in friction duration. Even with these stimuli, friction duration was a weak and poorly discriminated voicing cue. The 4th experiment showed that variations in the structure and duration of vowels are specific to the voicing contrast and minimally influence vowel identification. Acoustic analyses of /jus/ and /juz/ produced at normal and rapid rates revealed that the proportional durations of the semivowel transitions and vowel steady state differed reliable before /s/ and /z/, regardless of total vowel duration. Before /s/ the steady-state duration was .apprx. 45% that of the entire vowel, as compared with 65% before /z/. These proportional values remained stable across talkers and speaking rates. Postvocalic fricative voicing contrasts apparently may be encoded in the relative timing of articulatory events which produce the entire voiced portion of the syllable. Attunement to both the structure and duration of vowels as sources of perceptual information may then account for the minimal ambiguity of linguistic contrasts assumed to be cued by differences in vowel duration.