For the study, Lorimer Moseley of Oxford University and his colleagues recruited 10 participants, all of whom suffer from chronic pain in their right arm. The participants were asked to perform a set of movements with their right arm, under different conditions. In one condition, they observed their limb through a pair of binoculars, which magnified their hand to twice its normal size; in another, the binoculars were inverted so that their hands appeared smaller than they actually were.

As they performed the arm movements, the participants were asked to rate the amount of pain they experienced. Each one reported that the pain they felt became markedly worse when they moved their limb. Surprisingly though, every participant also reported that the extent to which their pain increased depended on how their vision had been manipulated. They reported the greatest increase in pain when they saw a magnified view of their hand, and the smallest increase when their hands were minified.

I think this TED talk by Vilayanur Ramachandran touches on same and is really interesting to watch.