Visual agnosias

Michael S Vaphiades DO (Dr. Vaphiades of the University of Alabama at Birmingham has no relevant financial relationships to disclose.)
Jonathan D Trobe MD, editor. (Dr. Trobe of the University of Michigan has no relevant financial relationships to disclose.)
Originally released April 7, 1999; last updated August 11, 2014; expires August 11, 2017

This article includes discussion of visual agnosias, Capgras syndrome, prosopagnosia, topagnosia, and visual object agnosia. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.

Overview

Visual agnosias are a group of disorders characterized by a patient's inability to recognize a visual target despite the preservation of mental and visual functions. In this article, the author reviews visual agnosias and related disorders, including Capgras syndrome, which is characterized by the delusion that closely related people have been replaced by replicas.

Historical note and terminology

Visual agnosia is characterized by the inability to recognize a visual target despite the preservation of mental and visual functions (Bender 1963). One of the first descriptions of a visual agnosia was provided by Munk in 1881 (Munk 1881). Munk noted that following bilateral partial occipital lobe ablation, a dog had a change in his responsiveness to familiar objects; the dog could see the objects but could not recognize them. In 1890 Lissauer distinguished between 2 forms of visual agnosia: apperceptive and associative. In the apperceptive form, the patient had impaired perception of the object. In the associative form, perception was intact but devoid of meaning due to impaired access to memory (Lissauer 1890; Riddoch et al 1999). In other words, apperceptive agnosics have visual deficits that prevent them from correctly perceiving a stimulus, whereas associative agnosics can perceive an object correctly but cannot associate the percept with a stored memory of that object (Delvenne et al 2004). In 1891, Freud introduced the term "agnosia," which was later defined as failure to recognize objects, not attributable to a defect in visual acuity, impaired cognition, or aphasia (Bender and Feldman 1972). Bender and Feldman found that a coexisting visual field defect was commonly associated with the visual agnosias, and the defect was usually a homonymous hemianopia or quadrantanopia (Bender and Feldman 1972). Typically, visual agnosia results from a structural brain lesion, most commonly an infarction in the domain of the posterior cerebral artery (Benson et al 1974). However, there are exceptions, one of which is autopagnosia, the inability to localize body parts either in a person (self or someone else) or in a picture. Autopagnosia is generally associated with a left parietal lobe neoplasm. It was not previously clear if this disorder was due to a deficit in interpreting body schema or an aphasia with which it is frequently associated. Guariglia and colleagues reported a man with a left corona radiata ischemic infarction and autopagnosia. There was no language disorder, cognitive impairment, or visuospatial disorder. The authors believed that this case supported the existence of a specific system in the brain devoted to processing body schema (Guariglia et al 2002). Capgras syndrome, a delusional state, has aspects that overlap visual agnosia and will, therefore, be discussed.

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