Intrinsic dynamics in human sensorimotor control of unilateral hand and forearm coordination

Abstract

Coordination dynamics is concerned with the underlying principles of cooperative\ud behavior among various body parts during coordinated activity. The intrinsic dynamics of\ud a multicomponent system stem from the innate behavioral tendencies borne out of the\ud inherent properties of the components, be it in their individual or coupled states, under\ud unregulated (or free-choice) conditions. A simple model of the human reach-and-grasp\ud system consisting of two components, namely, the hand and the forearm, unilaterally\ud engaged in the coordinative actions of manipulation and transport was devised for studying\ud the intrinsic dynamics via characterization of movement frequencies in various phasing\ud relationships. The Haken-Kelso-Bunz (HKB) Model provided the framework for\ud parameterizing the coordination behavior of this two-component movement system.\ud Participants were specifically instructed to choose their movement speeds for various\ud visually-guided rhythmic movement conditions in experimental trials conducted over two\ud consecutive days. A comparison of the natural frequencies of the components, before\ud coupling, and the preferred frequencies of the system performing various movement patterns, after coupling, revealed that the forearm was able to cycle at a higher natural rate\ud than the hand. The 0?? and 180?? relative phase patterns of movement had higher preferred\ud movement frequencies and less variability of frequency and relative phase than the\ud movement of the hand and the forearm coupled with a phase angle difference of 247.5??.\ud Hence, the former two patterns were relatively more stable. The natural frequency of\ud neither the hand nor the forearm was more correlated with the preferred frequency of the\ud hand-and-forearm system for all the three relative phases of 0??, 180??, and 247.5??. For all\ud the three movement conditions (with relative phases of 0??, 180??, and 247.5??), the natural\ud combined frequency, defined mathematically as the average of the sum of the natural\ud frequencies of the hand and the forearm, had a higher correlation with the preferred\ud frequencies than the association between the natural separated frequency, expressed\ud mathematically as the absolute difference between the natural frequencies of the hand and\ud the forearm, and the preferred frequencies. This was despite the fact that the natural\ud separated frequency was commonly used to represent aw in movement studies that\ud referenced the HKB Model