The rubber tool illusion reveals how body image modifies body schema.

Abstract

Rubber hand illusion and tool-use paradigms have been extensively used to investigate body representation. Although both approaches rely on multisensory integration and external object incorporation, they are typically studied in isolation. Here, we introduce a novel paradigm that combines these methods to investigate whether perceptual modifications to body representation can induce motor changes, and vice versa. First, participants completed a tool-use task, actively using a short or long grabber tool to move cubes. When asked to point toward the forearm midpoint, only long tool users exhibited a distal shift, denoting an expansion in motor representation. Next, participants experienced the "rubber tool illusion" by passively holding the same tool while observing a rubber hand grasp an identical-looking tool. Notably, participants holding a short tool exhibited an expanded forearm representation when they observed a synchronously stroked long tool during illusion. Control experiments revealed that this effect depended on prior active tool use, embodiment of the observed rubber hand/tool, and a length mismatch between the held and observed tools. These findings reveal for the first time that motor representation of forearm length, a component of body schema, can be modulated by changes in body image. (PsycInfo Database Record (c) 2025 APA, all rights reserved).