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Abstract
Purpose: The amount of stuttering produced by persons who stutter can be temporarily eliminated or substantially reduced during several known fluency-inducing conditions (FICs). One hypothesis put forth to explain this reduction was Wingates (1969; 1970) Modified Vocalization Hypothesis (MVH). Stated simply, Wingate proposed that the reduction in stuttering occurs because speakers do something different with their speech apparatus during the FICs, as compared to their normal speaking pattern. There has been much research aimed at examining this hypothesis, but the lack of experimental control of several possible confounding variables (e.g., speaking context, speech rate and instatement style used) limits the conclusions that can be drawn from these studies. Literature within and outside the stuttering community reveals that these issues likely affect data collection and interpretation, but no study has examined the nature of these confounds. The present study examined the effect of these issues using one of the most powerful FICs: the metronome effect. Method: This study involved 11 adult stutterers between the ages of 18 and 62 years old. Each participant completed a variety of tasks involving speaking to the beat of a metronome. A repeated-measures design was used to examine the relationship between several speech production variables (vowel duration, voice onset time, fundamental frequency, intraoral pressure, pressure rise time, transglottal airflow, and phonated intervals), and speaking context, instatement style, and speech rate. Results: The results revealed that instatement style and speech rate had a significant impact on the distribution of the main dependent variables, and on the specific dependent variables that are timed-based, including vowel duration, voice onset time, pressure rise time, and phonated intervals. Peak pressure was influenced by speaking context. Maximum airflow, vowel midpoint airflow, and fundamental frequency were not significantly impacted by speaking context, instatement style, or speech rate, with the exception of maximum airflow being altered by a large difference in speech rate. Conclusion: The results show the importance of considering speaking context, instatement style, and speech rate when examining vocalization variables during production of FICs. These issues must be considered when drawing conclusions about the importance of vocalization changes to the fluency resulting during the FICs.