Rhythmic tapping difficulties in adults who stutter: a deficit in Central Clock and/or Motor Implementation?

The study aims to better understand the origin of increased tapping variability and inaccuracy in people who stutter during paced and un-paced tapping. The overall question is to what extent these timing difficulties are related to a central clock deficit, a deficit in motor execution, or both.Finger tapping behavior of 16 adults who stutter (PWS) with different levels of musical training was compared with performance of 16 matching controls (PNS) in three finger tapping synchronization tasks ― a simple 1:1 isochronous pattern, a complex non-isochronous pattern, and a 4 tap:1 beat isochronous pattern ―, a continuation task (without external stimulation), and a reaction task involving aperiodic and unpredictable patterns. The results show that PWS exhibited larger negative asynchrony (expressed as phase angles), and increased synchronization variability (expressed as phase locking values) in paced tapping tasks, and that these differences from the PNS group were modulated by rhythmic complexity and musical training. The tapping asynchrony with a simple isochronous pattern correlated significantly with the average inter-tap duration, and with tap reaction times during the reaction task. The synchronization variability with a simple isochronous pattern correlated significantly with both the central clock and motor implementation variances as extracted during un-paced tapping, according to the Wing and Kristofferson’s model of timing.The results support the idea that increased tapping variability of PWS is associated with both a central clock and a motor execution deficit. The greater Negative Mean Asynchrony of PWS does not appear to be attributable to a deficit in time estimation but rather to a motor deficit. Several models and theories related to deficits in sensorimotor integration were considered to explain the interactions with beat strength, pattern complexity, and musical training.