We asked a student to stand on her left holding a pen so Sally could see the reflection of the pen in the mirror on her right (and she said she could). We then asked Sally to take the pen with her (nonparalyzed) right hand and write her name on a notepad on her lap. Imagine our astonishment when Sally reached straight toward the mirror and attempted to grab the reflection! When asked where the pen was, she replied with frustration: “The pen is inside the darned mirror, doctor.” On other occasions, she reached behind the mirror, groping for the pen, insisting that “the pen is behind the mirror.” It was as though her brain were saying, “This is a mirror reflection, so the pen is on my left. But left doesn’t exist in my universe, so the pen must be in the mirror. That is the only ‘solution’ to the problem.”
What is surprising is the illusion’s resistance to intellectual correction. Her high-level knowledge about mirrors and what they do cannot correct her behavior even after repeated failed attempts to grab the pen. Indeed, it is the other way around: her knowledge of mirror optics has been warped to accommodate the strange sensory world she is now trapped in (to the extent of rationalizing her action by saying things such as “The pen is inside the darned mirror, doctor”). We have dubbed this new neurological disorder (or “sign”) mirror agnosia.
Hope for Recovery?
Mirror agnosia is unlikely to be a deficit that is restricted to mirrors. In fact, we have seen patients recover temporarily from neglect (by irrigating the ear with cold water) but continue to reach for the pen in the mirror. We should regard it as a specific—if dramatic—manifestation of a more general disorder: an inability to deal with complex spatial relations caused by the right parietal damage. Recognizing a mirror image as a mirror image requires a peculiar dual representation in the brain: a mirage superimposed on reality (e). With a damaged right parietal lobe, Sally’s brain cannot handle this peculiar juxtaposition. Even a four-year-old child or an orangutan rarely confuses a mirror image of a banana for the real thing, but the older, wiser Sally does, despite her lifetime experience with mirrors.
Neglect is a common clinical problem. It is frustrating to therapists who try to educate the use of the left arm during the critical window of the first few weeks after a stroke; the patient’s indifference to her left side becomes an impediment to therapy. We found that with repeated coaxing, Sally would start reaching for the pen on the left, but when we came back after a few hours the mirror agnosia returned. Would repeated training sessions, spread over several days, finally correct her mirror agnosia? Would it get rid of the neglect entirely? This cure remains to be seen.
What is clear for now, though, is that studying patients with Sally’s deficits can give us valuable insight into how the brain constructs reality.
Note: This article was originally printed with the title, "Half a World".