Superimposition in interlimb rhythmic coordination

Von Holst (1939/1973) identified three processes of intersegmental rhythmic coordination: the magnet effect, the maintenance tendency, and superimposition. Superimposition, the augmenting or diminishing of amplitude (A), is believed to interact with the other two processes in such a way that the most stable organization will maximize A. The present experiment tests this hypothesis by having subjects oscillate hand-held pendulums in three different modes, one uncoupled (single pendulum oscillations) and two coupled (inphase (φ = 0) and antiphase (φ = π)). The order parameter dynamics of relative phase predict an increased phase attraction at φ = 0 resulting in greater A. In agreement with predictions, oscillations at φ = 0 were shown to (i) be more stable (that is, lower SD φ) and (ii) possess a greater A than at φ = π. Additionally, uncoupled A was only slightly greater than coupled A suggesting weak coupling. These results support the hypothesized relation between superimposition and the magnet effect and the strategy of modelling coupled oscillators without reference to A.