The effect of rhythm on inter-gestural coupling of onset and vowel gestures and predictive timing in stuttering

Abstract

In this study we investigate articulatory timing in fluent speech production in persons who stutter (PWS) and persons who do not stutter (PWNS) by focusing on consonant–vowel (CV)-timing, which refers to the coupling of onset consonant and vowel gestures, as well as on predictive timing, which describes the synchronization of the speech onset to a rhythmic event. These two timing mechanisms are particularly interesting to investigate in relation to stuttering, given that CV-timing is especially challenging for PWS and that they exhibit differences in predictive timing related to speech-motor and manual-motor tasks, suggesting that disturbances in inter-gestural coordination and auditory-motor integration may contribute to stuttering. To shed further light on this, we examine CV-timing and predictive timing under different rhythmic conditions.

Twenty German-speaking adults (10 PWS and 10 PWNS) were recorded using electromagnetic articulography (EMA). Participants produced target words that started with a bilabial onset, followed by a vowel (/a/, /o/, or /u/) and were embedded in a carrier phrase in four different conditions: Unpaced (speaking), Tapping (speaking while concurrently tapping), Metronome (synchronizing speech to a metronome), and Metronome+Tapping (speaking to a metronome while concurrently tapping).

We found evidence for both CV-timing and predictive timing differences between PWS and PWNS. Our results suggest that in general, PWS time CV gestures closer together. However, CV-timing differences were linked to condition in an unexpected way. As to predictive timing, PWS initiated their speech later to a metronome beat than PWNS but they did not differ when timing speech to their own finger tapping, indicating that motor-pacing may stabilize the speech motor system of PWS. In the Metronome+Tapping condition, the groups appeared to rely on different rhythmic cues. While PWNS timed their speech more towards the metronome beat, PWS synchronized their speech onset closer to the finger tap. We discuss that this difference could result from differences in CV-timing. Furthermore, the potential for future research on the interplay of non-verbal and verbal motor systems and the possible benefit for the stuttering population is discussed.