Dancing robots: The control theory of communication through movement

Abstract

This chapter summarizes work to understand various aspects of the communication that occurs through the movements of partners in a dance. The first part of the paper adopts the terminology of motion description languages and deconstructs an elementary form of the well-known popular dance, salsa, in terms of four motion primitives (dance steps). These motion primitives can be specified entirely by the motions of the dancer’s feet, and hence the motions can be effectively carried out by simple unicycle-like mobile robots. We describe an experiment in which ten performances by an actual pair of dancers are evaluated by judges and then compared in terms of several complexity metrics. An energy metric is also defined. Values of this metric are obtained by summing up the lengths of motion segments executed by wheeled robots replicating the movements of the human dancers in each of ten dance performances. Of all the metrics that are considered in this experiment, energy is the most closely correlated with the human judges assessments of performance quality. The second part of the paper discusses an enhanced form of (intermediate level) salsa in which upper body motions play a role in the steps of the dance. In this version, it is stipulated that the dancers must remain in physical contact by holding hands. The number of motion primitives is increased to eleven, and the requirement that the dancers’ hands must remain linked imposes constraints on the structure of the dance sequences. These constraints are discussed using simple ideas from topological knot theory. Using a natural Markov model to generate possible dance sequences, it is shown that because the topological constraints enforce syntactic constraints on the motion transitions, the entropy rate of the intermediate level salsa is smaller than that of the beginner level salsa. The chapter concludes with a brief discussion of the challenges and possible approaches to creating robotic movement that will be perceived as having artistic merit.