Visual agnosia
Encyclopedia
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 familiar objects or faces. This is distinct from blindness
, which is a lack of sensory input to the brain due to damage to the eye
, optic nerve
, or primary visual systems in the brain such as the optic radiations or primary visual cortex. 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. 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.
Careful analysis of the nature of visual agnosia has led to improved understanding of the brain's role in normal vision.
. Failure in high-level object recognition despite normal vision
is apperceptive visual agnosia. Associative visual agnosias are categorized by inability to identify objects due to impaired access to stored semantic information about the objects. 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.
Known clinical variants of visual agnosia include agnosias for prosopagnosia (agnosia for faces), pure word blindness (agnosias for words), agnosias for colors, agnosias for the environment such as known landmarks and simultanagosia which is the inability to perceive multiple objects in a visual scene.
Human eye
The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
to make sense of or make use of some part of otherwise normal visual stimulus and is typified by the inability to recognize familiar objects or faces. This is distinct from blindness
Blindness
Blindness is the condition of lacking visual perception due to physiological or neurological factors.Various scales have been developed to describe the extent of vision loss and define blindness...
, which is a lack of sensory input to the brain due to damage to the eye
Human eye
The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
, optic nerve
Optic nerve
The optic nerve, also called cranial nerve 2, transmits visual information from the retina to the brain. Derived from the embryonic retinal ganglion cell, a diverticulum located in the diencephalon, the optic nerve doesn't regenerate after transection.-Anatomy:The optic nerve is the second of...
, or primary visual systems in the brain such as the optic radiations or primary visual cortex. Visual agnosia is often due to damage, such as stroke
Stroke
A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
, in the posterior occipital
Occipital lobe
The occipital lobe is the visual processing center of the mammalian brain containing most of the anatomical region of the visual cortex. The primary visual cortex is Brodmann area 17, commonly called V1...
and/or temporal lobe
Temporal lobe
The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....
(s) in the brain.
The specific symptoms can vary depending on the cause of the agnosia
Agnosia
Agnosia is a loss of ability to recognize objects, persons, sounds, shapes, or smells while the specific sense is not defective nor is there any significant memory loss...
. Some sufferers are unable to copy drawings but are able to manipulate objects with good dexterity. 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.
Careful analysis of the nature of visual agnosia has led to improved understanding of the brain's role in normal vision.
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 drawDrawingDrawing is a form of visual art that makes use of any number of drawing instruments to mark a two-dimensional medium. Common instruments include graphite pencils, pen and ink, inked brushes, wax color pencils, crayons, charcoal, chalk, pastels, markers, styluses, and various metals .An artist who...
common objects. - Inability to copyCopyingCopying is the duplication of information or an artifact based only on an instance of that information or artifact, and not using the process that originally generated it. With analog forms of information, copying is only possible to a limited degree of accuracy, which depends on the quality of the...
drawings of objects. - AchromatopsiaAchromatopsiaAchromatopsia , is a medical syndrome that exhibits symptoms relating to at least five separate individual disorders. Although the term may refer to acquired disorders such as color agnosia and cerebral achromatopsia, it typically refers to an autosomal recessive congenital color vision disorder,...
, an impaired recognition of colorColorColor or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors...
. - ProsopagnosiaProsopagnosiaProsopagnosia is a disorder of face perception where the ability to recognize faces is impaired, while the ability to recognize other objects may be relatively intact...
, an impaired recognition of human faces. - ProsopamnesiaProsopamnesiaProsopamnesia is a rare neuropsychological deficit defined by an inability to remember faces. It can be subdivided into two different types, including a 'congenital' and 'acquired' version....
, an impaired remembrance of human faces.
Types
The two major types of visual agnosia are apperceptive and associative visual agnosiaAgnosia
Agnosia is a loss of ability to recognize objects, persons, sounds, shapes, or smells while the specific sense is not defective nor is there any significant memory loss...
. Failure in high-level object recognition despite normal vision
Visual perception
Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...
is apperceptive visual agnosia. Associative visual agnosias are categorized by inability to identify objects due to impaired access to stored semantic information about the objects. Patients with apperceptive visual agnosias cannot draw or copy drawings, whereas patients with associative visual agnosias appear to retain the neural circuits
Biological neural network
In neuroscience, a biological neural network describes a population of physically interconnected neurons or a group of disparate neurons whose inputs or signalling targets define a recognizable circuit. Communication between neurons often involves an electrochemical process...
necessary for object recognition without being aware of this ability. Associative visual agnosia is likely the result of disruption of connections between visual perception
Perception
Perception is the process of attaining awareness or understanding of the environment by organizing and interpreting sensory information. All perception involves signals in the nervous system, which in turn result from physical stimulation of the sense organs...
and verbal
Language
Language may refer either to the specifically human capacity for acquiring and using complex systems of communication, or to a specific instance of such a system of complex communication...
systems.
Known clinical variants of visual agnosia include agnosias for prosopagnosia (agnosia for faces), pure word blindness (agnosias for words), agnosias for colors, agnosias for the environment such as known landmarks and simultanagosia which is the inability to perceive multiple objects in a visual scene.
In popular culture
- A famous report on this condition is the title essay of Oliver SacksOliver SacksOliver Wolf Sacks, CBE , is a British neurologist and psychologist residing in New York City. He is a professor of neurology and psychiatry at Columbia University, where he also holds the position of Columbia Artist...
' book, The Man Who Mistook His Wife for a HatThe Man Who Mistook His Wife for a HatThe Man Who Mistook His Wife for a Hat and Other Clinical Tales is a 1985 book by neurologist Oliver Sacks describing the case histories of some of his patients. The title of the book comes from the case study of a man with visual agnosia...
. - The murder suspect in the Picket FencesPicket FencesPicket Fences is a 60-minute American television drama about the residents of the fictional town of Rome, Wisconsin, created and produced by David E. Kelley. The show initially ran from September 18, 1992, to June 26, 1996, on the CBS television network in the United States...
episode "Strangers" supposedly suffered from agnosia. - The patient in the HouseHouse (TV series)House is an American television medical drama that debuted on the Fox network on November 16, 2004. The show's central character is Dr. Gregory House , an unconventional and misanthropic medical genius who heads a team of diagnosticians at the fictional Princeton-Plainsboro Teaching Hospital in...
episode "Adverse EventsAdverse Events"Adverse Events" is the third episode of the fifth season of House and the eighty-ninth episode overall. It first aired on September 30, 2008. Breckin Meyer guest starred as an artist who has an unexplained visual problem.- Plot :...
" suffered from agnosia. - A peculiar type of visual agnosia resulting from experimental brain surgery drives the plot of the 6th volume of Osamu TezukaOsamu Tezukawas a Japanese cartoonist, manga artist, animator, producer, activist and medical doctor, although he never practiced medicine. Born in Osaka Prefecture, he is best known as the creator of Astro Boy, Kimba the White Lion and Black Jack...
's PhoenixPhoenix (manga)is a manga series by Osamu Tezuka. Tezuka considered Phoenix his "life's work"; it consists of 12 books, each of which tells a separate, self-contained story and takes place in a different era. The plots go back and forth from the remote future to prehistoric times. The cycle remains unfinished...
series. - In Saya no UtaSaya no Utais a visual novel by Nitroplus with horror elements. The original plot is written by Gen Urobuchi.Like Nitroplus' heavily Mythos-inspired Demonbane series, Saya no Uta's plot is somewhat Lovecraftian...
, 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 PreacherPreacher (comics)Preacher is a comic book series created by writer Garth Ennis and artist Steve Dillon, published by the American comic book label Vertigo , with painted covers by Glenn Fabry....
, a one eyed waitress named Lori has Visual Agnosia.
See also
- AgnosiaAgnosiaAgnosia is a loss of ability to recognize objects, persons, sounds, shapes, or smells while the specific sense is not defective nor is there any significant memory loss...
- Color agnosiaColor agnosiaColor agnosia , is a medical or psychological condition that prevents a person from correctly associating hue names with common objects. The sufferer retains the ability of distinguishing hues...
- ProsopagnosiaProsopagnosiaProsopagnosia is a disorder of face perception where the ability to recognize faces is impaired, while the ability to recognize other objects may be relatively intact...
- BlindnessBlindnessBlindness is the condition of lacking visual perception due to physiological or neurological factors.Various scales have been developed to describe the extent of vision loss and define blindness...
- Klüver-Bucy syndromeKlüver-Bucy syndromeKlüver-Bucy syndrome is a behavioral disorder that occurs when both the right and left medial temporal lobes of the brain malfunction. The amygdala has been a particularly implicated brain region in the pathogenesis of this syndrome. The syndrome is named for Heinrich Klüver and Paul...