Agnosia lets you see a face perfectly and still not know who it is
People with agnosia have working eyes, ears or noses and intact memories, yet the brain fails to turn the signal into recognition. One patient, asked about breakfast, said the word sounded familiar but did not speak to him. Sigmund Freud coined the name in 1891, from the Greek for not knowing.
Agnosia usually follows brain injury or neurological disease, from strokes and dementia to head trauma, infection, inherited conditions or developmental disorders. Damage typically lies in the occipital or parietal lobes, often at the border between occipital and temporal regions, part of the brain's ventral visual stream. Crucially it strikes a single sense, leaving other thinking skills in place. Researchers increasingly suspect a breakdown in top-down handling of perceptual information.
Visual agnosia splits into two broad kinds. In the apperceptive form, linked to damage at the back of the right hemisphere, people can trace an object's outline but struggle to sort it into a category. In the associative form, linked to damage on both sides, they see the object but cannot name it. Prosopagnosia, face blindness, is a specific associative type: friends, relatives and colleagues become strangers, while other objects are recognised normally. Speech agnosia, or pure word deafness, leaves hearing, speaking and reading intact while spoken words turn to unrecognisable noise, though some patients still tell whether a voice is male or female.
The ideas grew out of 19th-century neurology. Carl Wernicke described receptive aphasia in 1874, Kussmaul blamed word deafness on destruction in the left temporal lobe in 1877, and Heinrich Lissauer proposed in 1890 that recognition could fail either at early perception or at the stored representation of the object. Oddly, people who dramatically regain sight after blindness can show significant or even total agnosia.
There is essentially no direct cure. Many patients at first do not realise anything is wrong, a lack of awareness called anosognosia that can breed denial. Presenting information through an unaffected sense can help, along with occupational or speech therapy depending on the cause. Face-blind people may rely on verbal descriptions and other cues, and those with visual agnosia can lean on organising strategies such as grouping clothes on different hangers.
Source: Agnosia
