How a Robotic Body Swap Reveals the Processing of Space and Time in the Brain
Whether standing upright or recovering from a stumble, the brain must continuously interpret sensory information that is already out of date by the time it arrives. These unavoidable delays—only a few hundred milliseconds—create a fundamental challenge for balance control and become longer with age and neurological disease. Yet how the brain compensates for this temporal lag, and how it blends information about the body’s mechanical properties with the timing of sensory feedback, has remained largely unknown.
In a new paper published in Science Robotics, Patrick Forbes together with colleagues from the University of British Columbia, developed a robotic “body-swap” system that allows researchers to alter the physics of a person’s body in real time while they stand. By coupling participants to a balance robot that simulates their body as an inverted pendulum, the team could independently modify two key spatial properties—inertia (how heavy the body feels) and viscosity (how resistant or destabilizing movement feels)—as well as impose a 200 ms sensorimotor delay, effectively creating a controlled mismatch between motor actions and their sensory consequences.
The authors found that reducing inertia or adding negative viscosity produced instability patterns nearly identical to those caused by a 200 ms delay. Participants also perceived these spatial changes as equivalent to the feeling of balancing with delayed feedback. Remarkably, when the robot combined the imposed delay with a “heavier” or “more damped” virtual body, participants immediately regained stability—without any training.
These findings reveal that the nervous system processes spatial and temporal properties of balance through overlapping internal representations rather than treating them as separate dimensions. This discovery provides a new framework for understanding how the brain stabilizes posture under uncertainty and suggests that carefully tuned mechanical interventions may help compensate for neurological delays.
Beyond neuroscience, the work offers promising applications for robotics, where integrating spatial and temporal control into a unified architecture may enhance balance in bipedal machines, and for clinical rehabilitation, where robotic or wearable devices could one day help older adults and patients with sensory or motor delays avoid falls.
In a new paper published in Science Robotics, Patrick Forbes together with colleagues from the University of British Columbia, developed a robotic “body-swap” system that allows researchers to alter the physics of a person’s body in real time while they stand. By coupling participants to a balance robot that simulates their body as an inverted pendulum, the team could independently modify two key spatial properties—inertia (how heavy the body feels) and viscosity (how resistant or destabilizing movement feels)—as well as impose a 200 ms sensorimotor delay, effectively creating a controlled mismatch between motor actions and their sensory consequences.
The authors found that reducing inertia or adding negative viscosity produced instability patterns nearly identical to those caused by a 200 ms delay. Participants also perceived these spatial changes as equivalent to the feeling of balancing with delayed feedback. Remarkably, when the robot combined the imposed delay with a “heavier” or “more damped” virtual body, participants immediately regained stability—without any training.
These findings reveal that the nervous system processes spatial and temporal properties of balance through overlapping internal representations rather than treating them as separate dimensions. This discovery provides a new framework for understanding how the brain stabilizes posture under uncertainty and suggests that carefully tuned mechanical interventions may help compensate for neurological delays.
Beyond neuroscience, the work offers promising applications for robotics, where integrating spatial and temporal control into a unified architecture may enhance balance in bipedal machines, and for clinical rehabilitation, where robotic or wearable devices could one day help older adults and patients with sensory or motor delays avoid falls.
