ゴム手の幻想

Proprioception is the brain's ability to sense where your limbs are positioned relative to your body and surroundings. It relies on the brain's control and feedback signals to track limb location, enabling you to walk without hitting obstacles, sit on chairs, and perform coordinated movements. This sense integrates information from vision, touch, and proprioceptive inputs to create an accurate body representation in space.

The illusion works by synchronously stroking a participant's hidden real hand and a visible rubber hand with paintbrushes for 10 minutes. The brain integrates the simultaneous visual and tactile inputs, creating a false sense of body ownership over the rubber hand. This demonstrates that vision and touch work together to establish which limbs belong to the body, even when proprioceptive signals contradict this multisensory integration.

Participants rate statements on a scale from strongly disagree to strongly agree. Strong agreement with statements about feeling brushing on the rubber hand indicates illusion success. However, disagreement with statements about the rubber hand looking like their own arm and disagreement about altered proprioception shows that vision influences touch and body position, but not the reverse. This pattern confirms the illusion affected perception without changing visual appearance or spatial awareness.

The premotor cortex, an area responsible for controlling motor actions, shows greater activation during the illusion compared to asynchronous brushing conditions. This region connects visual and somatosensory areas, particularly the posterior parietal cortex, providing an anchor between visual, tactile, and proprioceptive information. This neural activity pattern suggests the premotor cortex integrates multisensory signals to create the sense of body ownership.

In schizophrenia patients, the illusion is stronger, induces faster, and produces increased perceptual reports even during asynchronous brushing when the illusion should not occur. These effects can be mimicked in healthy individuals using drugs like ketamine or amphetamine. This suggests that distorted body ownership in schizophrenia involves altered multisensory integration in brain regions responsible for representing the body in space.

Yes, the illusion can be adapted therapeutically using mirrors to trick the brain into seeing two complete limbs. This approach helps reorganize connections within multisensory pathways associated with the missing limb, potentially alleviating phantom limb pain in amputees. By manipulating visual and proprioceptive signals, researchers can reduce the distressing sensations that persist after limb loss.

Synchronous brushing—where the real and rubber hands are stroked simultaneously—creates a temporal match between visual and tactile inputs that the brain interprets as belonging to the same limb. Asynchronous brushing breaks this temporal correlation, preventing the illusion. This demonstrates that the brain relies on timing and multisensory correspondence to determine body ownership, showing how investigating visual awareness and inattentional blindness relates to broader perceptual mechanisms.