Visual agnosia is an impairment in recognition of visually presented objects. It is not due to a deficit in vision (acuity, visual field, and scanning), language, memory, or low intellect. There are two types of visual agnosia: apperceptive agnosia and associative agnosia.
Recognition of visual objects occurs at two primary levels. At apperceptive level, the features of the visual information from the retina is put together to form a perceptual representation of an object. At associative level, the meaning of an object is attached to the perceptual representation and the object is identified. If a person is unable to recognize objects because he cannot perceive correct forms of the objects, although his knowledge of the objects is intact, it is apperceptive agnosia. If a person correctly perceives the forms and has knowledge of the objects, but cannot identify the objects, it is associative agnosia.
Visual agnosia is often due to bilateral damage in the posterior occipital and/or temporal lobe(s) in the brain.
Read more about Visual Agnosia: Classification, Symptoms, Pathophysiology, In Popular Culture
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