Different Stable Patterns between Intra- and Inter-personal Systems: Experimental Study on Inter-limb Tapping Coordination

Different Stable Patterns between Intra- and Inter-personal Systems: Experimental Study on Inter-limb Tapping Coordination Kentaro Kodama (kodamakentaro@nii.ac.jp) Department of Informatics, School of Multidisciplinary Science, The Graduate University for Advanced Studies, 2-1-2 Hitotsubashi, Chiyoda-ku, Tokyo, Japan. Ryosaku Makino (ryosaku@nii.ac.jp) Department of Informatics, School of Multidisciplinary Science, The Graduate University for Advanced Studies, 2-1-2 Hitotsubashi, Chiyoda-ku, Tokyo, Japan. Nobuhiro Furuyama (furuyama@nii.ac.jp) Information and Society Research Division, National Institute of Informatics, 2-1-2 Hitotsubashi, Chiyoda-ku, Tokyo, Japan, Department of Informatics, School of Multidisciplinary Science, The Graduate University for Advanced Studies, and Graduate Schools of Tokyo Institute of Technology. Abstract To reveal the differences between intra- and inter-personal systems in terms of the perceptual effect on the stability of inter-limb coordination, the present study conducted a finger- tapping experiment in in-phase and anti-phase mode. We investigated a between-subjects factor (the intra-/inter- personal condition), and a within-subject factor (the phase mode). In the intra-personal condition, participants bimanually tapped their index fingers, paced by a metronome, with the frequency gradually increasing from 1 Hz to 3 Hz. In the inter-personal condition, pairs of participants were asked to perform the same task, but to use their right or left index finger, while sitting side-by-side and looking at each other’s fingers moving. Analysis showed that the average number of phase transitions, average time-to-transition and standard deviation of the relative phase differed between the intra- personal system and inter-personal system. Some results do not agree with the predictions of theoretical model proposed in previous studies on inter-limb coordination.  Keywords: Inter-limb coordination; Finger Tapping Task; Perceptual Effect; Dynamical Systems Approach Introduction To reveal the differences between intra- and inter-personal coordination systems, a finger-tapping experiment was conducted in which two phase modes (in-phase and anti- phase) were manipulated as a factor. The present study had two objectives. One objective was to reveal the role of perceptual information in inter-limb coordination. For this, we conducted a finger-tapping experiment, comparing the intra-personal condition with the inter-personal condition. Because the tapping task required participants to utilize visual, auditory, and haptic information (e.g., looking at a moving finger, listening to auditory metronome stimuli as well as the sounds of tapping, and touching the surface of the desk), the effect of multi-modal perceptual information could be examined (Kodama and Furuyama, 2010). We investigated not only the intra-personal system, which involves neural and mechanical coupling between limbs, but also the inter-personal system, which involves visual coupling through watching the other’s movements. We could thus focus on the perceptual effect on inter-limb coordination. The other objective was to see how generally the existing model on human inter-limb coordination, called the Haken-Kelso-Bunz (HKB) model, could be applied to human inter-limb coordination in the intra-personal system and in the inter-personal system. The first application of self-organization theory to human inter-limb coordination was attempted by Scott Kelso (Kelso, 1984) and his colleagues (Haken et al., 1985). Since then, research on this topic has developed tremendously. In this approach, called the dynamical systems approach, the general findings are that bimanual coordination is more stable in the in-phase mode than in the anti-phase mode; one of the most important observations is that phase transitions take place unidirectionally from the anti-phase mode to the in-phase mode when the required oscillation frequency reaches or exceeds a critical point. These findings led to the proposal of a theoretical model, called the Haken-Kelso- Bunz (HKB) model (Haken et al., 1985). The above findings have been confirmed for inter- personal coordinated movement (e.g., swinging of pendulums or legs) (Schmidt et al., 1990, 1998). Phase transitions in inter-personal systems indicate that visual information involves coordinated movement because inter- personal systems do not involve mechanical or neural couplings between limbs, unlike intra-personal systems. Schmidt et al. (1998) suggested that the self-organization principle of intra-personal systems governs inter-personal systems as well but that the coupling strength between limbs is stronger in intra-personal systems. However, most studies on coordinated movement have dealt with either intra- or inter-personal coordination of a pair of oscillators (fingers, legs, pendulums, etc.) wiggling or swaying in the air; that is, these studies did not address