Effects of Masked and Delayed Auditory Feedback on Fundamental Frequency Modulation in Vocal Vibrato

Rosemary A. Lester-Smith, PhD, CCC-SLP | University of Texas in Austin

Dr. Rosemary A. Lester-Smith received an NSDA Travel Award to the 2019 Fall Voice Conference and presented a research poster that contributes to our understanding of expert vocal control and informs the development of strategies to improve vocal control in individuals with neurological voice disorders like essential vocal tremor. Dr. Lester-Smith in the Department of Communication Sciences and Disorders at the University of Texas in Austin.

Dr. Lester-Smith shared, “This meeting provided opportunities to discuss current research on neurological voice disorders with other scientists and clinicians and to develop new collaborative research directions. In addition, it provided both undergraduate and graduate student opportunities to meet leading scientists and clinicians in the field and to see the benefit of collaboration between speech-language pathologists, otolaryngologists, singing teachers, and voice scientists. Also, this NSDA Research Travel award supported the dissemination of research on neurological voice disorders to a diverse audience and facilitated the development of new research ideas.” Below is an abstract of her presentation.

Introduction: Vocal vibrato is a singing technique characterized by modulation of the fundamental frequency (fo) with a rate of 5-7 Hz and an extent of 6-8% (Prame, 1994; Shipp et al., 1980; Sundberg, 1995). Previous studies on auditory-motor control of vibrato in singers reported inconsistent effects of altered auditory feedback on the modulation rate and extent (Deutsch & Clarkson, 1959; Shipp et al., 1988). In Shultz-Coulon and Battmer’s study (as cited in Shipp et al., 1988) there was no change in the rate when auditory feedback was masked with noise in one singer, although the extent became more variable. Deutsch & Clarkson (1959) reported that the rate decreased when auditory feedback was delayed by 500 ms in one singer. In contrast, Shipp et al. (1988) reported that the rate increased when auditory feedback was delayed by 120, 300, and 500 ms in three singers, but did not significantly change when auditory feedback was delayed by 200 or 400 ms. Shipp et al. (1998) did not find significant differences in the extent with delayed auditory feedback. As a result of these inconsistent findings, it is unclear how altered auditory feedback affects the rate and extent of fo modulation in vibrato. It is important to understand expert control of modulated voice in singers to inform future studies of disordered control of modulated voice in individuals with voice disorders. For example, essential vocal tremor (EVT) is a neurogenic voice disorder characterized by involuntary modulation of fo (Duffy, 1995). Similar to vibrato, EVT is characterized by an average fo modulation rate of 5 Hz and extent of 5- 10% (Barkmeier-Kraemer et al., 2011; Lester et al., 2013). Although EVT and vibrato have acoustical similarities, it is unknown whether auditory-motor control differs for undesired modulation of voice in EVT and desired modulation of voice in vibrato.

Purpose: The current study examined the effect of masked and delayed auditory feedback on the rate and extent of fo modulation in singers producing vibrato.

Methods: Ten classically-trained singers produced vibrato in sustained vowels across three conditions. In the noise and babble conditions, participants’ auditory feedback was masked with either pink noise or multi-talker babble or unmasked in control trials. In the delay condition, auditory feedback was delayed by 200 or 300 ms or undelayed in control trials. Auditory feedback was amplified by about 10 dB SPL relative to the microphone signal to mask air-conducted feedback. Acoustical analyses of the rate and extent of fo modulation were performed using custom-written Praat scripts (Boersma & Weenink, 2019).

Results: Noise masking, babble masking, and delayed auditory feedback did not have a significant effect on the rate or extent of fo modulation.

Conclusions: The results of the current study suggest that classically-trained singers do not rely on their auditory feedback to control the extent or rate of fo modulation in vibrato. This experimental protocol will be used to investigate the effects of masked and delayed auditory feedback on fo modulation in individuals with essential vocal tremor with the aim of informing behavioral intervention for essential vocal tremor.

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