The brain never ceases to impress me. In my last post I told you about blindsight. People with this condition are able to react to objects in their visual field, even though they are cortically blind (see video here of a blind man, navigating his way accurately through a cluttered hallway). People with blindsight don’t see but still respond to things in their visual fields. There is a condition that appears to be the reverse of blindsight, i.e. people who see, but fail to respond to what they see.
These people do not respond to stimuli presented to a part of their visual field (usually the left side), even though their vision is intact. They do not orient their eyes or head toward anything on their left side. If it comes from the left, it doesn’t seem to exist. In their everyday life they may neglect the walls, the cars or the people on their left side and even the food on the left side of their plate. Some also only shave or put makeup on the right side of their face, ignoring the left side. These people are not blind, if their attention is drawn to something on their left, they can see it and identify it. They just don’t seem to care. This is not a problem of vision, but of awareness and it is called hemispatial neglect.
In the book, Fractured Minds, Jenni A. Ogden tells the story of Janet, a middle-aged, energetic, intelligent woman who enjoyed landscape painting and pottery. The first sign of her condition was apparent during her 50th birthday celebration. She managed to blow all the candles out on the right side of her cake, seemingly unaware of leaving the candles on the left side burning. When tested with neuropsychological test is was apparent that Janet suffered from hemispatial neglect. When reading aloud, she read fluently but missed two or three words of the left of every single line. When she wrote a letter to her daughter all the words were written down the right side of the page.
When asked to put numbers in on a clock face, Janet included all the right numbers from 1 to 12, but wrote them all on the right side of the clock face and left the other side blank. Tests also showed that Janet not only neglected the left side of things she saw, but also the left side of visual images she invoked in her mind.
Visual neglect is the most common form of neglect, but not the only form. Anything that can be sensed, can be neglected. Janet also showed signs of motor neglect. She felt her left arm did not belong to her and did not use it. She called it “that hunk of meat” and asked for it to be removed from her bed. When she dressed in the hospital, she put her right arm in the right sleeve of her nightgown, but left her left shoulder bare. When asked, she declined to put her left arm into the sleeve, saying she would rather leave it as it was. This was by the way not the result of a loss of motor function.
Of course people who ask their doctors to remove their arm or leg from their beds (Janet is far from being the only example) sound as if they have totally lost their minds. This is not so. What makes a request like Janet’s seem so preposterous, is precisely that it is coming from a person who is sensible and lucid in most other ways.
The parietal lobes are concerned with the spatial layout of the world, enabling us to navigate our surroundings without bumping into things. Hemispatial neglect is common immediately following a stroke in the right parietal lobe leading to neglect in the left side of the visual field. Usually the neglect is not persistent for more than 3 months. Here is a video with more information on blindsight and visual neglect: http://youtu.be/ADchGO-0kGo
According to this video, posted by oggie114 on YouTube.com, dogs can also suffer from hemispatial neglect following a stroke: