From The New York Times:
Whether made of highly polished metal or of glass with a coating of metal on the back, mirrors have fascinated people for millennia: ancient Egyptians were often depicted holding hand mirrors. With their capacity to reflect back nearly all incident light upon them and so recapitulate the scene they face, mirrors are like pieces of dreams, their images hyper-real and profoundly fake. Mirrors reveal truths you may not want to see. Give them a little smoke and a house to call their own, and mirrors will tell you nothing but lies.
To scientists, the simultaneous simplicity and complexity of mirrors make them powerful tools for exploring questions about perception and cognition in humans and other neuronally gifted species, and how the brain interprets and acts upon the great tides of sensory information from the external world. They are using mirrors to study how the brain decides what is self and what is other, how it judges distances and trajectories of objects, and how it reconstructs the richly three-dimensional quality of the outside world from what is essentially a two-dimensional snapshot taken by the retina’s flat sheet of receptor cells. They are applying mirrors in medicine, to create reflected images of patients’ limbs or other body parts and thus trick the brain into healing itself. Mirror therapy has been successful in treating disorders like phantom limb syndrome, chronic pain and post-stroke paralysis.
More here.