What is agnosia?

Quick Answer
Inability to identify objects or persons using one or more of the senses, even though the basic sensory modalities are not defective.
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Causes and Symptoms

Agnosia is typically caused by brain damage produced by head injury, stroke, infection, or carbon monoxide poisoning that sometimes causes lesions in the parietal and temporal lobes of the brain, significantly impairing an individual’s cognitive processes. Agnosia can also result from neurological disorders, especially if the occipitotemporal border of the ventral stream is damaged. The three main types of agnosia are visual agnosia, auditory agnosia, and tactile agnosia. Some types of agnosia have been found to be genetic.

Victims of agnosia may not recognize objects, persons, shapes, sounds, or smells but retain their cognitive abilities in other areas. Sufferers often have difficulty recognizing the geometric features of an object or a face and determining the use of the object or whether the face is familiar. Some patients can see only one object at a time, while others see multiple objects but recognize only one at a time. Some do not consciously perceive the orientation of an object but will reach for it with a correctly oriented grasp.

Treatment and Therapy

Since no specific treatment or direct cure has been found for agnosia, treatment is generally symptomatic and supportive. Depending on the etiology, some patients with agnosia can be assisted in compensating for disorder deficits through speech or occupational therapy.

In order to treat the specific problems of a particular patient, the primary cause of the disorder must be determined. Physical examination often identifies primary deficits in individual senses or communication that are not related to agnosia. Images of the brain obtained through computed tomography (CT) scanning or magnetic resonance imaging (MRI) are used to characterize any brain lesions and to check for atrophy that may suggest a degenerative disorder.

Perspective and Prospects

Case studies reporting selective inabilities to recognize faces or objects were reported throughout the nineteenth century. Starting in 1947, studies led by Joachim Bodamer, a German neurologist, helped to develop theories about visual agnosia. Different victims show different types and levels of impairment. Evidence indicates that there may be a specific face perception system in the brain. In the early twenty-first century, a form of congenital prosopagnosia, or face blindness, was identified. It is inherited by 2.5 percent of the population. As more research uncovers details about various types of agnosia, medical recognition, effective treatments, and specific therapies will be enhanced.


Brust, John. Current Diagnosis and Treatment in Neurology. New York: McGraw-Hill Medical, 2007.

Farah, Martha J. Visual Agnosia. 2d ed. Cambridge, Mass.: MIT Press, 2004.

Parker, James N., ed. The Official Patient’s Sourcebook on Agnosia: A Revised and Updated Directory for the Internet Age. San Diego, Calif.: Icon Health, 2002.

National Institute of Neurological Disorders and Stroke. "NINDS Agnosia Information Page." National Institute of Neurological Disorders and Stroke, Oct. 2, 2007.