- • The brain keeps a representation of which things are part of our body. This sense of ownership is easily manipulated using brushing of the skin or movement of a limb to create an illusion of ownership over an inanimate object, such as a rubber hand.
- • We induced a sense of ownership of an artificial finger using movement of the index finger without vision of the hands. As cutaneous receptors had been anaesthetised, this illusion depended on proprioceptive signals from muscle receptors.
- • In addition, we found a new grasp illusion in which perceived distance between the index fingers decreases when subjects hold an artificial finger.
- • These results increase understanding of how the brain generates our body representation and may help in understanding diseases in which the sense of ownership is disrupted.
Abstract Body ‘ownership’ defines which things belong to us and can be manipulated by signals from cutaneous or muscle receptors. Whether signals from muscle proprioceptors on their own influence perceived ownership is unknown. We used finger-joint movement to induce illusory ownership of an artificial finger without vision. We coupled the subject's index finger to an artificial finger 12 cm above it. The experimenter held the subject's other index finger and thumb on the artificial finger and passively moved them congruently or incongruently for 3 min with the index finger and the grasping index finger and thumb intact or anaesthetised. When intact, congruent movement (19 subjects) reduced perceived vertical distance between index fingers to 1.0 (0.0, 2.0) cm [median (IQR)] from 3.0 (3.0, 4.0) cm with incongruent movement (P < 0.01). Simply grasping the artificial finger reduced perceived spacing between the grasping and test index fingers from 6.0 (5.0, 9.0) cm to 3.0 (3.0, 6.0) cm (P < 0.01), a new grasp illusion. Digital anaesthesia eliminated this grasp effect, after which congruent movement still reduced the perceived spacing between the index fingers to 1.0 (0.0, 2.75) cm compared to 4.0 (3.25, 6.0) cm with incongruent movement (P < 0.001). Subjects more strongly agreed that they were holding their own finger after congruent but not incongruent movement (P < 0.01). We propose that the brain generates possible scenarios and tests them against available sensory information. This process can function without vision or motor commands, and with only one channel of somatic information.