Rhythmic tapping to a moving beat: motion kinematics overrules motion naturalness.

Beat induction is the cognitive ability that allow humans to listen to a regular pulse in music and move in synchrony with it. Although auditory rhythmic cues are known to induce more consistent synchronization than flashing visual metronomes, this asymmetry can be canceled out by visual moving metronomes. Here, we investigated whether the naturalness of the visual motion or its kinematics could provide a synchronization advantage over flashing metronomes. Subjects tap in sync with visual isochronous metronomes defined by vertically or horizontally accelerating and decelerating motion, either congruent or not with natural gravity, and then continue tapping with no metronome. We found that motion kinematics was the predominant factor determining rhythm synchronization, as accelerating moving metronomes in either cardinal direction produced more precise and predictive tapping than decelerating or flashing conditions. Notably, a Bayesian observer model revealed that error correction during tapping synchronization and regression towards the mean in accuracy during tapping continuation in the absence of external cues are optimal control strategies independently of the moving properties of the visual metronomes. Our results support the notion that accelerating visual metronomes convey a strong sense of beat as seen in the cueing movements of an orchestra director.