When they cant tell one object from another

The part of the brain where an image is processed,known as the lower visual cortex,was similar in SM and in normal test subjects. But in and around the area where SM had a lesion,he had decreased brain activity. Its not that his brain does not respond at all to visual inputit certainly does, said Marlene Behrmann,a neuroscientist at Carnegie Mellon and one of the studys authors. Rather,the problem is that his brain is unable to uniquely assiagn that visual input to a known object,like a harmonica.

But the most surprising finding was that there was also abnormal activity in the patients intact left hemisphere,in the same small area where the lesion was on the right side. This led to the insight that theres this sort of cooperativity with the other hemisphere that is needed, Behrmann said.

By understanding exactly what brain regions are affected and how,Behrmann believes that it might one day be possible to develop devices to aid patients with such visual recognition disorders.Sindya N. Bhanoo