Visual agnosia
Visual agnosia is the inability of the brain to make sense of or make use of some part of otherwise normal visual stimulus and is typified by the inability to recognize. The literal meaning of agnosia is "without knowledge". Without damage to the retina, optic nerve, cornea, pupil, or anything for that matter involving the eye-an individual suffering from this is able take sensory input [see], but unable to perceive, interpret and organize that information using our long-term memory in order to understand the environment. The brain cannot make the connection between sensory information and past experience. Visual agnosia is often due to damage, such as stroke, in the posterior occipital and/or temporal lobe(s) in the brain.
The specific symptoms can vary depending on the cause of the agnosia. Some sufferers are unable to copy drawings but are able to manipulate objects with good dexterity.[1] Commonly, patients can describe objects in their visual field in great detail, including such aspects as color, texture and shape but are unable to recognize them. Similarly, patients can often describe familiar objects from memory despite their visual problems.[2]
Careful analysis of the nature of visual agnosia has led to improved understanding of the brain's role in normal vision.
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[edit] Symptoms and subtypes
Any of the following may be considered symptoms of visual agnosia. Some of them are also regarded as subtypes:
- Inability to identify common objects.
- Inability to draw common objects.
- Inability to copy drawings of objects.
- Achromatopsia, an impaired recognition of color.
- Prosopagnosia, an impaired recognition of human faces.
- Prosopamnesia, an impaired remembrance of human faces.
[edit] Types
The two major types of visual agnosia are apperceptive and associative visual agnosia. Failure in high-level object recognition despite normal vision is apperceptive visual agnosia.[3] Associative visual agnosias are categorized by inability to identify objects due to impaired access to stored semantic information about the objects.[4] Patients with apperceptive visual agnosias cannot draw or copy drawings, whereas patients with associative visual agnosias appear to retain the neural circuits necessary for object recognition without being aware of this ability. Associative visual agnosia is likely the result of disruption of connections between visual perception and verbal systems.[5]
Known clinical variants of visual agnosia include prosopagnosia (inability to recognize faces), pure word blindness (inability to recognize words), agnosias for colors (inability to differentiate colors), agnosias for the environment (inability to recognize landmarks etc.) and simultanagosia (inability to sort out multiple objects in a visual scene). [6]
[edit] In popular culture
- A famous report on this condition is the title essay of Oliver Sacks' book, The Man Who Mistook His Wife for a Hat.
- The murder suspect in the Picket Fences episode "Strangers" supposedly suffered from agnosia.
- The patient in the House episode "Adverse Events" suffered from agnosia.
- Val Kilmer's character suffers from visual agnosia in the film At First Sight.
- A peculiar type of visual agnosia resulting from experimental brain surgery drives the plot of the 6th volume of Osamu Tezuka's Phoenix series.
- In Saya no Uta, the protagonist undergoes drastic emergency brain surgery to save his life from a fatal traffic accident that kills his parents. As a side effect of this life-saving surgery, the protagonist is left with a bizarre form of visual agnosia that makes the world appear to him as "warped", where non-organic objects resemble organic structures of putrid flesh and people appear to be monsters to him.
- In the comic book series Preacher, a one eyed waitress named Lori has Visual Agnosia.
[edit] See also
[edit] References
- ^ Visual Agnosia - A Disorder of the Ventral Stream, Student Web Pages, Department of Applied Health Sciences, University of Waterloo
- ^ Candace N. Palmer. An Examination of Visual Agnosia, Stephen F. Austin State University
- ^ Shelton PA, Bowers D, Duara R, Heilman KM (1996). "Apperceptive visual agnosia: a case study". Brain Cogn. 25 (1): 1–23. doi:10.1006/brcg.1994.1019. PMID 8043261.
- ^ Anaki D, Kaufman Y, Freedman M, Moscovitch M (2007). "Associative (prosop)agnosia without (apparent) perceptual deficits: a case-study". Neuropsychologia. 48 (8): 1658–71. doi:10.1016/j.neuropsychologia.2007.01.003. PMID 17320120.
- ^ Carlson, Neil R. “Analysis of Visual Information: Role of the Visual Association Cortex. Physiology of Behavior, 9. Boston, Mass., USA: Pearson Education, Inc., 2007. ISBN 0-205-46724-5.
- ^ Biran I. and Coslett H.B. (2003). Visual Agnosia.Current neurology and neuroscience reports, 3(6):508 - 512. ISSN 1528-4042. DOI: 10.1007/s11910-003-0055-4
- Farah, Martha J. The Cognitive Neuroscience of Vision. Fundamentals of Cognitive Neuroscience, 3. Malden, Mass., USA: Blackwell Publishers, 2000. ISBN 0-631-21403-8.
