Rhythmic tapping difficulties in adults who stutter: A deficit in beat perception, motor execution, or sensorimotor integration?

Abstract

Objectives: The study aims to better understand the rhythmic abilities of people who stutter and to identify which processes potentially are impaired in this population: (1) beat perception and reproduction; (2) the execution of movements, in particular their initiation; (3) sensorimotor integration.

Material and method: Finger tapping behavior of 16 adults who stutter (PWS) was compared with that of 16 matching controls (PNS) in five rhythmic tasks of various complexity: three synchronization tasks - a simple 1:1 isochronous pattern, a complex non-isochronous pattern, and a 4 tap:1 beat isochronous pattern -, a reaction task to an aperiodic and unpredictable pattern, and a reproduction task of an isochronous pattern after passively listening.

Results: PWS were able to reproduce an isochronous pattern on their own, without external auditory stimuli, with similar accuracy as PNS, but with increased variability. This group difference in variability was observed immediately after passive listening, without prior motor engagement, and was not enhanced or reduced after several seconds of tapping. Although PWS showed increased tapping variability in the reproduction task as well as in synchronization tasks, this timing variability did not correlate significantly with the variability in reaction times or tapping force. Compared to PNS, PWS exhibited larger negative mean asynchronies, and increased synchronization variability in synchronization tasks. These group differences were not affected by beat hierarchy (i.e., "strong" vs. "weak" beats), pattern complexity (non-isochronous vs. isochronous) or presence versus absence of external auditory stimulus (1:1 vs. 1:4 isochronous pattern). Differences between PWS and PNS were not enhanced or reduced with sensorimotor learning, over the first taps of a synchronization task.

Conclusion: Our observations support the hypothesis of a deficit in neuronal oscillators coupling in production, but not in perception, of rhythmic patterns, and a larger delay in multi-modal feedback processing for PWS.

Fig 1. Summary of the five tasks: 1:1_ISO_SYNC—Synchronization task with a quadruple metered isochronous pattern; 0:1_ISO_REPRO–Reproduction, without any external reference, of a quadruple metered isochronous pattern, after listening passively to it; 1:4_ISO_SYNC: Synchronization task with a quadruple metered isochronous pattern, where only the strong beats (one every four) were marked by an auditory stimulus; NONISO_SYNC—Synchronization task with a quadruple metered non-isochronous pattern; REACT–Reaction task to an unpredictable and aperiodic pattern.

The small lines indicate the metronome beats of an 8- beat cycle. The black dots indicate the auditory stimuli that were played to the participants. The grey triangles indicate the participants finger taps.

Fig 2. (a) Average finger reaction time and (b) variability of this reaction time, in the condition REACT during which participants had to follow aperiodic and unpredictible auditory stimuli.

People who stutter (PWS, N = 16) are compared with typical adults without speech disorder (PNS, N = 16).

Fig 3. (a) Coefficient of Variation (CV), inversely related to the degree of isochrony of the reproduced pattern, measured over the very first taps or the stabilized phase of ISO_REPRO, compared to the stabilized phase of the synhcronization task 1:1_ISO_SYNC.

People who stutter (PWS, N = 16) are compared with typical adults without speech disorder (PNS, N = 16). (b) Average Periodicity Error (PE) when reproducing the specific 500ms period of the previously heard isochronous pattern of the condition ISO_REPRO, over the very first taps (first 8-beat cycle) or the more stabilized phase (second and third 8-beat cycles) of the condition.

Fig 4. (a) Average Phase Angle and (b) Phase Locking Value, for the synchronization task with an isochronous pattern (1:1_ISO_SYNC), over the very first 8-beat cycle of taps or the two next cycles.

Fig 5. Tapping Force (in arbitrary unit) on the “strong” vs. “weak” beats of a 8-beat isochronous pattern, in which all the beats were marked by an auditory stiumulus (1:1_ISO_SYNC), or only the strong ones (1:4_ISO_SYNC), and on the “half-beat” pulses of a non-isochronous pattern (NONISO_SYNC).

People who stutter (PWS, N = 16) are compared to with matched control particpants without speech disorders (PNS, N = 16).

Fig 6. Average Phase Angle on the “strong” vs. “weak” beats of a 8-beat isochronous pattern, in which all the beats were marked by an auditory stiumulus (1:1_ISO_SYNC), or only the strong ones (1:4_ISO_SYNC), and on the “half-beat” pulses of a non-isochronous pattern (NONISO_SYNC).

People who stutter (PWS, N = 16) are compared to with matched control particpants without speech disorders (PNS, N = 16).

Fig 7. Phase Locking Value on the “strong” vs. “weak” beats of a 8-beat isochronous pattern, in which all the beats were marked by an auditory stiumulus (1:1_ISO_SYNC), or only the strong ones (1:4_ISO_SYNC), and on the “half-beat” pulses of a non-isochronous pattern (NONISO_SYNC).

People who stutter (PWS, N = 16) are compared to with matched control particpants without speech disorders (PNS, N = 16).