Human body schema exploration: Analyzing design requirements of Robotic Hand and Leg Illusions

Understanding the integration of user-proximal robots in the body schema of their human users has a distinct potential to improve human-robot interaction. Robotic devices can help to investigate the psychological fundamentals of body schema integration. While the Rubber Hand Illusion experiment indicates how artifacts can be perceived as a part of the own body, it relies on a passive limb that does not perform motions during the examinations. Novel setups aim at Robotic Hand/Leg Illusions induced by robotic devices which imitate human motions. Although such devices distinctly extend experimental possibilities, their design is rather proprietary and unstructured up to now. This paper analyzes the requirements of robotic hand and leg illusion setups based on systematic discussion of a multidisciplinary team of researchers from engineering and psychology. In a comparative study, requirements are collected and structured, their similarities and differences are determined, and the most important ones are extracted yielding design implications. The requirements with the highest priority are setup characteristics that concern the occurrence and quality of the illusion, i.e., hiding the real limb, anatomical plausibility, visual appearance, temporal delay, and software-controlled experimental conditions. Based on the results, the design of future robotic devices for the exploration of human body schema integration might be guided and supported.