Speech Dynamics and Resilience of Speech Production: Can Typically Fluent Adults Adapt to Long-Latency Delayed Auditory Feedback?

Purpose: Delayed auditory feedback (DAF) is a potent speech perturbation that can induce disfluencies and speech errors along with slowing speaking rate in typical speakers. Typical speakers vary considerably in their susceptibility to DAF. In this study, we tested if typical speakers can completely suppress DAF effects or show a gradual, incomplete adaptation to DAF. Understanding the degree and time course of adaptation has clinical relevance as auditory manipulations are emerging as treatment options for several disorders. Method: Thirty-eight speakers read a single passage under nonaltered auditory feedback followed by 10–12 repeated readings of a different passage under 250-ms DAF. Disfluency rate (DR), articulation rate (AR), and reading duration were measured for each reading. The analysis used parametric statistics and growth models to test for change over time. Results: Over repeated readings of the same passage under DAF, DR decreased and AR increased compared to the first DAF reading for each speaker. Ten speakers reached our criteria for suppression of DAF effects, while a larger number approached the adaptation criteria for one of the dependent variables. Conclusions: Extended exposure to DAF during repeated readings promotes significant adaptation, but most speakers did not fully suppress the influence of DAF. Incomplete adaptation is more consistent with a slow process of modifying speech production strategies rather than rapid cognitive adjustments.