Development of Perception of Weight from Human or Robot Lifting Observation

Human interaction is based, among other factors, on non verbal and implicit communication. By observing the action of someone else we can automatically infer several non obvious details of what's happening, as the goal of the agent, his mood and even some features of the object he is using, e.g., if it is heavy or light. This action reading skill is developed very early in life and constitutes a fundamental basis for the development of collaboration. A similar capacity to implicitly communicate weight would be desirable also in a humanoid robot, to allow for a natural preparation for hand-over between the robot and the human partner. Here we have investigated how the ability to infer weight from human action observation develops during childhood and whether such ability generalizes to the observation of a humanoid robot. In particular, the robot was not programmed to perform human-like lifting actions, but just to replicate a property of human lifting deemed as determinant for weight reading: exhibiting a velocity proportional to object weight. Our results suggest that although 6-year-olds can already judge weight from the observation of a lifting action, they cannot generalize this skill to simplified robotic actions as the ones proposed here.