Distinct Timing Mechanisms Produce Discrete and Continuous Movements

Abstract

The differentiation of discrete and continuous movement is one of the pillars of motor behavior classification. Discrete movements have a definite beginning and end, whereas continuous movements do not have such discriminable end points. In the past decade there has been vigorous debate whether this classification implies different control processes. This debate up until the present has been empirically based. Here, we present an unambiguous non-empirical classification based on theorems in dynamical system theory that sets discrete and continuous movements apart. Through computational simulations of representative modes of each class and topological analysis of the flow in state space, we show that distinct control mechanisms underwrite discrete and fast rhythmic movements. In particular, we demonstrate that discrete movements require a time keeper while fast rhythmic movements do not. We validate our computational findings experimentally using a behavioral paradigm in which human participants performed finger flexion-extension movements at various movement paces and under different instructions. Our results demonstrate that the human motor system employs different timing control mechanisms (presumably via differential recruitment of neural subsystems) to accomplish varying behavioral functions such as speed constraints.

Asymmetric Transfer of Visuomotor Learning between Discrete and Rhythmic Movements

“…For example, the movement speed-accuracy tradeoff was different in the two classes of movements (Smits-Engelsman et al, 2002), which seems to support the third hypothesis. On the other hand, a theoretical study suggested that discrete movement can be constructed from rhythmic movement (i.e., supporting the second hypothesis) by imposing timekeeper mechanisms on the controller (Huys et al, 2008).…”

“…The third hypothesis assumes that rhythmic and discrete movements are two different (or partially different) classes of movements (Sternad et al, 2000;Buchanan et al, 2003). These hypotheses have been examined from behavioral (Buchanan et al, 2003;van Mourik and Beek, 2004), theoretical (Schöner, 1990;Huys et al, 2008;Ronsse et al, 2009), and neuronal (Spencer et al, 2003(Spencer et al, , 2007Schaal et al, 2004) perspectives. The current consensus is that rhythmic movements are not mere concatenations of discrete movements (i.e., the first hypothesis has been ruled out).…”

Fitts' law is not continuous in reciprocal aiming

“…Importantly, the drift coefficients numerically express the system's vector field in phase space, that is, they allow recovery of the flow that allows for the unambiguous qualification of dynamical systems (cf. Strogatz 1994;Huys et al 2008 and averaged across blocks of 10 trials with adjacent ID e 's. From the first two drift coefficients (representing the velocity vector's x and y components), we determined for each bin the angles u between its neighbouring velocity vectors and extracted its maximum value (u max ).…”

Anticipation of tennis-shot direction from whole-body movement: The role of movement amplitude and dynamics

“…In other words, phase flows capture the causation underlying the time evolution of such dynamical systems. Of late, the (topological) structure in phase flows has been used as a conceptual tool for the categorization of (discrete and rhythmic) movements (Huys, Studenka, Rheaume, Zelaznik, & Jirsa, 2008;Jirsa & Kelso, 2005). Phase flow patterns, however, may also underlie the perceptual recognition of distinct motor processes (Perdikis & Jirsa, 2010; see also Muchisky & Bingham, 2002).…”