The New York Times:
Object agnosia is a rare disorder in which an individual cannot visually recognize objects. In the case of a patient known as SM, he mistook a harmonica for a cash register.
Researchers from Carnegie Mellon and Princeton University studied SM’s brain and discovered that it was affected not only in the portion of the right hemisphere that had been damaged in a car accident, but also in his structurally intact left hemisphere.
They performed functional M.R.I. brain scans on the patient and report their findings in the journal Neuron.
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.
“It’s not that his brain does not respond at all to visual input — it certainly does,” said Marlene Behrmann, a neuroscientist at Carnegie Mellon and one of the study’s authors.
Rather, the problem is that his brain is unable to uniquely assign that visual input to a known object, like a harmonica.
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