MIRROR AGNOSIA

Normal people rarely confuse the mirror image of an object with a real object so long as they realize they are looking into a mirror. We rep ort a new neurological sign, 'mirror agnosia', following right parieta l lesions in which this ability is severely compromised. We studied fo ur right hemisphere stroke patients who had left visual field 'neglect '-i.e. they were indifferent to objects in their left visual field eve n though they were not blind. We then placed a vertical parasagittal m irror on each patients' right so that they could clearly see the refle ction of objects placed in the (neglected) visual field. When shown a candy or pen on their left, the patients kept banging their hand into the mirror or groped behind it attempting to grab the reflection they did not reach for the real object on the left, even though they were m entally quite lucid and knew they were looking into a mirror. Remarkab ly, all four patients kept complaining that the object was 'in the mir ror', 'outside my reach' or 'behind the mirror'. Thus, even the patien ts' ability to make simple logical inferences about mirrors has been s electively warped to accommodate the strange new sensory world that th ey now inhabit. The finding may have implications for understanding ho w the brain creates representations of mirror reflections.