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The authors studied pattern stability and error correction during in-phase and antiphase 4-ball fountain juggling. To obtain ball trajectories, they made and digitized high-speed film recordings of 4 highly skilled participants juggling at 3 different heights (and thus different frequencies). From those ball trajectories, the authors determined and analyzed critical events (i.e., toss, zenith, catch, and toss onset) in terms of variability of point estimates of relative phase and temporal correlations. Contrary to common findings on basic instances of rhythmic interlimb coordination, in-phase and antiphase patterns were equally variable (i.e., stable). Consistent with previous findings, however, pattern stability decreased with increasing frequency. In contrast to previous results for 3-ball cascade juggling, negative lag-one correlations for catch–catch intervals were absent, but the authors obtained evidence for error corrections between catches and toss onsets. That finding may have reflected participants’ high skill level, which yielded smaller errors that allowed for corrections later in the hand cycle. [authors summary]

The relationship between point-of-gaze and ball movements in three-ball juggling was examined as a function of expertise, pattern and tempo. Five intermediately skilled and five expert jugglers performed the standard and reverse cascade at three tempos, while point-of-gaze and ball movements were recorded simultaneously. Scaled to the size of the ball patterns, the experts made smaller point-of-gaze movements than the intermediates, especially in the horizontal direction and in the standard cascade. In both skill groups, point-of-gaze and ball movements were often 1 : 1 frequency locked in the horizontal direction, whereas in the vertical direction 1 : 2 frequency locking also occurred. In the latter direction, the 1 : 1 ratio prevailed in the intermediates and the 1 : 2 ratio in the experts. In addition, the incidence of the 1 : 1 ratio decreased and that of the 1 : 2 ratio increased with increasing tempo. Furthermore, in the vertical direction, increasing tempo resulted in a weaker 1 : 1 locking, whereas the strength of the 1 : 2 ratio remained unaffected by tempo. In the horizontal direction, the strength of the 1 : 1 locking was higher on average in the reverse cascade than in the standard cascade. We conclude that expertise in juggling is reflected by an overall reduction in the extent to which the balls are visually tracked, and that task constraints such as tempo and juggling pattern affect the visual search patterns of both expert and intermediate jugglers. [authors summary]

To uncover the underlying control structure of three-ball cascade juggling, we studied its spatiotemporal properties in detail. Juggling patterns, performed at fast and preferred speeds, were recorded in the frontal plane and subsequently analyzed using principal component analysis and serial correlation techniques. As was expected on theoretical grounds, the principal component analysis revealed that maximally four instead of the original six dimensions (3 balls x 2 planar coordinates) are sufficient for describing the juggling dynamics. Juggling speed was shown to affect the number of dimensions (four for the fast condition, two for the preferred condition) as well as the smoothness of the time evolution of the eigenvectors of the principal component analysis, particularly around the catches. Contrary to the throws and the zeniths, and regardless of juggling speed, consecutive catches of the same hand showed a markedly negative lag-one serial correlation, suggesting that the catches are timed so as to preserve the temporal integrity of the juggling act. [authors summary]

The circle map provides a general mathematical model for the mode-locking behavior observed in systems of coupled oscillators. From this theoretical perspective, multifrequency tapping was studied. Three experiments were conducted in which skilled drummers participated. The results were in qualitative agreement with the dynamical features of the circle map. The stability of behavior was affected by the movement frequency at which the multifrequency relations were performed. Attraction to lower order ratios (predominantly showing Farey relations) was observed. In some situations bistability and hysteresis occurred, implying that the system was situated in the supercritical domain of the circle map where resonance zones overlap. Furthermore, the results suggest that multifrequency tapping is characterized by an asymmetrical coupling in that the influence of the fast hand on the slow hand is the strongest. [authors summary]

It is argued that the proportional duration model provides an inadequate route into the problem of timing in skilled movements. It is theoretically shallow and lacks the predictive power to guide a research programme. An alternative, task-dynamical approach is proposed and exemplified in a study of relative timing in juggling. The adopted methodology emphasizes the need to first identify the major temporal constraints on the task and its key relative timing variable(s), and then to construct specific hypotheses regarding both the invariant and the variant properties of these relative timing variable(s).[author summary]

A natural-physical approach is pursued in uncovering basic timing and phase relations in human rhythmic movement. The approach is based on the theory of nonlinear oscillatory motion, entrained by continuously and discretely distrib- uted forcing. In the context of juggling three balls in a figure-eight pattern, a preliminary modeling attempt of the cyclical hand motion suggested that the dynamics underwriting juggling are captured best by a discretely kicked, highly nonlinear, self-sustained oscillator. Discretely kicked, nonlinear oscillators may be characterized by regime diagrams that depict the periodic (phase-locked) and quasiperiodic (not phase-locked) regimes in which the system can operate depending on the magnitude of the kicks. This article provides evidence for 2-quasiperiodicity and near, but not perfect, phase locking between tl/tf and tu/tf (where tl is the mean time that the hands move loaded with a ball, tu is the mean time that the hands move empty, and tf is the mean flight time of the balls). Jugglers perform along the boundaries of Arnol'd tongues (representing complete phase locking) in a regime diagram without actually entering into them. With the help of Denjoy's decomposition of phase modulation into a fast and a slow mode, the deviation from the potential minimum defined by complete phase locking can be understood. The frequency ratios within the continuous relative phase between the two juggling hands reveal a Farey type of phase-locking structure, allowing a qualitative insight into which regimes jugglers position themselves when asked to speed up or slow down their act. Modulation of the hand movements increases when timing constraints become more severe (e.g., when the number of balls in the air increases). The modified standard map promises to he an adequate tool in analyzing the phase progression in juggling. All in all, the results favor an understanding of rhythmic movement in terms of discretely forced, nonlinear dynamics, rather than fully autonomous, self-sustaining oscillators.[author summary]