Vilayanur Ramachandran, a neurologist at the University of California, San Diego, knows a thing or two about the wildly varying ways that people look at the world.
Brain damage can produce startling perceptual effects.
Take for instance the stroke patients that Ramachandran and his colleagues, Eric Altschuler and Steven Hillyard, have studied recently. People with injury to the right parietal lobe of the brain may remain clear-headed but tend to ignore everything on their left side, a condition called left hemisphere neglect. The condition usually wears off in a few weeks, but it sometimes lingers on for years. While patients have neglect, they will eat off only the right side of a plate of food, draw only half an object, and shave only half their face. They can see objects to the left only if someone else calls attention to them.