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Agnosia is a rare neuropsychological symptom defined as a failure of recognition that cannot be directly attributed to elementary sensory defects, dementia, attentional disturbances, aphasia, or unfamiliarity with external stimuli. Agnosia is modality specific; the patient who fails to recognize material presented through one sensory modality (e.g., vision) can do so successfully in another (e.g., audition). Agnosias are most commonly caused by vascular lesions (interruptions of blood supply to the brain), either to cortical areas that process high-level sensory or semantic information or to the white matter fibers that connect sensory association areas with semantic systems.

Types of Agnosia
Visual Agnosias

The patient with visual agnosia cannot identify visually presented material even though language, memory, and general intellectual functions are relatively preserved. The unrecognized visual object can ...

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