Evolved Electrophysiological Soft Robots

Abstract

The embodied cognition paradigm emphasizes that both bodies and brains combine to produce complex behaviors, in contrast to the traditional view that the only seat of intelligence is the brain. Despite recent excitement about embodied cognition, brains and bodies remain thought of, and implemented as, two separate entities that merely interface with one another to carry out their respective roles. Previous research co-evolving bodies and brains has simulated the physics of bodies that collect sensory information and pass that information on to disembodied neural networks, which then processes that information and return motor commands. Biological animals, in contrast, produce behavior through physically embedded control structures and a complex and continuous interplay between neural and mechanical forces. In addition to the electrical pulses flowing through the physical wiring of the nervous system, the heart elegantly combines control with actuation, as the physical properties of the tissue itself (or defects therein) determine the actuation of the organ. Inspired by these phenomena from cardiac electrophysiology (the study of the electrical properties of heart tissue), we introduce electrophysiological robots, whose behavior is dictated by electrical signals flowing though the tissue cells of soft robots. Here we describe these robots and how they are evolved. Videos and images of these robots reveal lifelike behaviors despite the added challenge of having physically embedded control structures. We also provide an initial experimental investigation into the impact of different implementation decisions, such as alternatives for sensing, actuation, and locations of central pattern generators. Overall, this paper provides a first step towards removing the chasm between bodies and brains to encourage further research into physically realistic embodied cognition. Introduction and Background The fields of evolutionary robotics and artificial life have seen a great deal of emphasis on embodied cognition in recent years [Cheney et al. (2013); Bongard (2013); Rieffel et al. (2013); Auerbach and Bongard (2012); Hiller and Lipson (2012a); Lehman and Stanley (2011); Auerbach and Bongard (2010a,b); Pfeifer et al. (2007); Hornby et al. (2001); Lipson and Pollack (2000)]. There is even a paradigm called embodied cognition, which argues that the specifics of the embodiment (such as the morphology) are Figure 1: Current flowing through an evolved creature. The legend for voltage within each cell (colors) is given in Fig. 3. vital parts of the resulting behavior of the system: It argues that the co-evolutionary connection between body and brain is more deeply intertwined than the body simply acting as a minimal physical interface between the brain and the environment [Pfeifer and Bongard (2006)]. Recent work in evolutionary robotics has shown that complex behaviors can arise when co-evolving bodies and brains. At one end of the spectrum, Auerbach and Bongard (2010b) demonstrated the evolution of physical structures that had no joints or actuators, and evolved to cover the largest distance in a controlled fall due to gravity. While that work exemplifies the evolution of behavior emerging from morphology alone, it does not co-evolve any actuation or control. Auerbach and Bongard (2010a) then evolved the placement of CPG controlled rotational joints between cellular spheres, thus co-evolving morphology and control. Cheney et al. (2013) evolved locomoting soft robots made of multiple different materials: two passive voxels of differing rigidity and two actuated voxel types that expanded cyclically via out-of-phase central pattern generators (CPGs). While this work added a variety of soft materials and a new type of actuation, the pairing of muscle types directly to a CPG again reflected a focus on evolving morphology rather than sophisticated neural control. Many examples in the literature include the co-evolution of a robot morphology with an a