Electromyography focused on activeness and passiveness in embodied interaction: Toward a novel interface for co-creating expressive body movement

In expressive bodily movement created by one person and his or her partner, they feel as if their bodies are united. In such an inseparable relationship, a process to physically feel activeness and passiveness is important. The objective of this study is to capture activeness and passiveness in bodily interaction. We focused on myoelectric (ME) potential, by which the difference in time of generation and amplitude between voluntary and reactive movements can be estimated. A system for measuring ME potential in bodily interaction was developed. This system comprises a board that slides only in a front-back direction to simplify bodily interaction, an liner encoder, active electrodes for surface electromyography, and an amplifier. Experiments showed that for active movement, the increase in ME potential was earlier and the amplitudes of the ME potential were larger when compared with those for passive movement. We also attempted to distinguish between active and passive movements using the amplitude of the ME potential in embodied interaction, with fixing the relationship between active and passive roles. The concordance rate was more than 80%; thus, the validity of this method was confirmed. Moreover we examined the degree of correspondence between the estimated active or passive status by the proposed determining method and the subjective sensation by button-report in embodied interaction without fixing active-passive roles. The concordance rate was 68%. This result suggested there is discrepancy between the subjective sensation and physical state when the roles of the pair change dynamically in creating improvised bodily-expression.