Octopus arm search strategies over complex surfaces

Abstract Despite the extreme flexibility of the octopus’s arms and their resulting near infinite possible configurations, the octopus effectively controls its arms during a wide variety of behaviors, including locomotion, foraging, excavation, exploration, and manipulation. If appropriately characterized, the octopus’s biomechanical properties and control strategies could be implemented in the development of a soft robotic limb with the same range of capabilities. When operating without visual feedback, the octopus must rely on the complex chemotactile sensory system within its suckers, and in these conditions sucker recruitment plays a prominent role in search behavior, causing the arm to conform to surface features in the environment. However, how this mechanism is used to search over the complex and convoluted surfaces in the octopus’s natural habitat is unknown. Here, we investigate the strategies the octopus uses to search for a reward hidden among a row of multiple small openings of a task space, and how it uses multiple arms to search three parallel versions of this task space. We found that when the arm encounters multiple openings in a surface, it performs a distal to proximal search pattern, starting with the farthest openings within reach then working its way proximally with a preference for searching each opening in succession. This strategy would allow the octopus to use its highly flexible limbs to perform an exhaustive search pattern over complex surfaces.