Stuttering inhibition via visual feedback at normal and fast speech rates

Immediate and drastic reductions in stuttering are found when speech is produced in conjunction with a variety of second signals (for example, auditory choral speech and its permutations, and delayed auditory feedback). Initially, researchers suggested a decreased speech rate as a plausible explanation for the reduction in stuttering as people who stutter produced speech under second signals. However, this explanation was refuted by research findings that demonstrated reductions in stuttering at both normal and fast speech rates under second signals. Recent studies have also demonstrated significant reductions in stuttering from second signals delivered via the visual modality. However, the question as to whether stuttering can be substantially reduced at normal and fast speech rates under visual speech feedback conditions has yet to be answered.

The current study investigated stuttering frequency reduction at normal and fast speech rates across different visual speech feedback conditions relative to a no-visual feedback condition.

Ten adults who stutter recited memorized tokens of eight to 13 syllables under five visual speech feedback conditions at both normal and fast speech rates. Visual speech feedback conditions consisted of participants viewing the lower portion of their face (that is, lips, jaw, and base of the nose) on a monitor as they produced the aforementioned utterances. Conditions consisted of (1) no-visual feedback condition, (2) 0 ms (simultaneous visual speech feedback), (2) a 50-ms delay, (3) a 200-ms delay, and (4) a 400-ms delay.

A significant main effect of visual speech feedback on stuttering frequency was found (p= 0.001) with no significant main effect of speech rate or the interaction between speech rate and visual speech feedback. Relative to the no-visual feedback condition, the feedback conditions produced reductions in stuttering ranging from 27% (0 ms) to 62% (400 ms). Post-hoc comparisons revealed that all of the delay conditions differed significantly from the simultaneous feedback (p= 0.017) and the no-visual feedback conditions (p= 0.0002) while no significant differences between delay conditions (that is, 50, 200, and 400 ms) were observed.

The current findings demonstrate the capabilities of visual speech feedback signals to reduce stuttering frequency that is independent of the speaker's rate of speech. Possible strategies are suggested to transfer these findings into naturalistic and clinical settings, though further research is warranted.