If these brain regions are damaged - by an injury or a tumor - it can lead to prosopagnosia: The affected have problems with the perception of faces, even if their visual system is intact and they are able to recognize everything else well.
For some prosopagnosicians, the whole world has become faceless. The New York neuropsychologist Oliver Sacks reported in his bestselling book about a professor at a conservatoire who not only lost the ability to recognize faces and occasionally confused his wife with a hat, but also suspected faces where none existed: "On the street, he pats hydrants and parking meters as he passes by because he thinks they are children; graciously he addresses carved posts and is amazed if they give no answer. "
While other patients know they see a face, they can not identify it. A soldier who was wounded in the head in 1944, all faces came to the same after: as strangely flat, white, oval plates with large dark eyes. However, he could still imagine the faces of people he had seen before his injury. Another patient described his impairment as follows: "I can clearly see the eyes, the nose and the mouth, but I can not form a picture of it. They all seem to be drawn in chalk on a black blackboard. "Some prosopagnosicians can no longer tell animals or even single animals. A hobby ornithologist lost the ability to differentiate between blackbird, finch, and star after a head injury; a farmer was no longer able to tell the faces of his cows, though he still knew they were cows. A guard in a natural history museum confused his own reflection with the image of a monkey. display
Some researchers see in prosopagnosia a kind of reversal of the Capgras syndrome. While Capgras patients recognize faces, but their brains do not connect them with the corresponding feelings, and even close people therefore seem strange to them, Prosopagnosiker respond emotionally to familiar faces: The gauges register a physical arousal. However, even with good acquaintances, people can not tell who they are facing.=== Rüdiger Vaas