Preponderance of Lead Voice Onset Times in Stutterers under Varying Constraints
Viswanath, Nagalapura S., Rosenfield, David B., Communication Disorders Quarterly
Differences between stutterers and nonstutterers in temporal organization of fluent speech may offer clues to the elemental basis of fully elaborated, perceptible stuttering events. Guided by this hypothesis, we investigated voice onset time--the interval between voice onset and upper articulatory stop release--in voiced stop consonants under varying constraints. Under variation of rate, lexical stress location, and location of key words beginning with voiced stops, the stutterers realized voiced stops by voicing before release (prevoicing), whereas the controls realized voiced stops by voicing following the release. The significance of this phonetic strategy difference for understanding and treating stuttering is discussed.
The study of timing and sequencing of gestures underlying the fluent and disfluent speech of stutterers has gained impetus with recent advances in speech technology and models of speech production. The issue of timing has been raised in relation to (a) perceptible stuttering events such as part-word repetitions (Viswanath & Neel, 1995) and (b) perceptibly fluent utterances (e.g., Agnello, 1975; Hillman & Gilbert, 1977; Zimmerman, 1980). Partly as consequence of these studies, several researchers have suggested that stutterers' intermittent (perceptible) speech breakdowns, frequently recognized as "moments of stuttering," are but the tip of the iceberg (Adams & Runyan, 1981, Zebrowski, Conture, & Cudahy, 1985). This suggestion carries the strong implication that even when stutterers appear to be fluent, they may be subtly aberrant. Consistent with this suggestion, Viswanath (1989) and Viswanath and Rosenfield (1991) proposed that such subtle aberrancies are likely in utterance locations where stutterers typically experience their greatest difficulty, namely, the beginning of words in relation to variables such as lexical stress, rate, and word location that predispose stutterers to stutter.
Under this general rubric, several investigators (Agnello & Wingate, 1972; Hillman & Gilbert, 1977; Jancke, 1994; Metz, Conture, & Caruso, 1979; Watson & Alfonso, 1982) have examined voice onset times (VOT) in perceptibly fluent speech of stutterers. VOT is defined as the interval between onset of two gestures during the course of a stop production:
1. onset of vocal fold vibrations and
2. its upper articulatory release (Lisker & Abramson, 1964; see Note).
As a measure of intergestural temporal coordination, VOT has many things to recommend it:
1. It is a well-recognized articulatory dimension underlying voiced-voiceless distinctions of stops in many languages.
2. It can be easily and reliably measured using acoustic techniques.
3. It is a well-researched dimension in the initial syllables of words.
This is a fortunate circumstance for stuttering research because the beginning of words is the most likely location for stuttering disruption (Wingate, 1979).
Generally, VOT studies in stutterers were explicitly or implicitly motivated by the following question: "How fast a stutter begins voicing after stop release?" The idea was that slower onset of voicing signals laryngeal involvement that serves as a basis for discoordination (Agnello & Wingate, 1972; Healy & Gutkin, 1984; Hillman & Gilbert, 1977; Jancke, 1994; Metz et al., 1979; Watson & Alfonso, 1982). Thus, Watson and Alfonso used the simple reaction time paradigm to compare initiation of voicing to a response-and-stop release to a signal. Because the question mentioned above determines the design of a study, the bulk of the research on VOT in stutterers has involved the study of long- and short-lag VOTs of voiceless and voiced stops. Researchers have neglected the lead VOT continuum in their investigations. Because English permits alternative realizations of fluent voiced stops, either with lead or short-lag VOTs, it is interesting to ask whether stutterers show a preference for either of the two strategies. …