It is evident, from all of this work, that the brain’s representation of the body can often be fooled simply by scrambling the inputs from different senses.  If sight and touch say one thing, however absurd, even a lifetime of proprioception and a stable body image cannot always resist this.  (Individuals may be more or less suseptible to such illusions, and one might imagine that dancers or athletes, who have an exceptionally vivid sense of where their bodies are in space, may be harder to fool in this way).

The body illusions Ehrsson is exploring are very much more than party tricks; they point to the ways in which our body ego, our sense of self, is formed from the coordination of senses – not just touch and vision but proprioception and perhaps vestibular sensation, too.  Ehrsson and others favour the idea that there are “multisensory” neurons, perhaps at a number of places in the brain, which serve to coordinate the complex (and usually consistent) sensory information coming into the brain.  But if this is interfered with – by nature or experiment – our seemingly unassailable certainties about the body and the self can vanish in an instant.

Oliver Sacks, Hallucinations.