Visual agnosia is the inability to recognize objects despite having no damage to the eyes or intelligence. There are two types: apperceptive agnosia, which is the inability to recognize objects, and associative agnosia, which is the inability to understand the function of objects. People with the condition can compensate by relying on other senses. There is currently no cure.
Visual agnosia is a medical condition in which the afflicted person can see an object placed in front of them but cannot figure out what the object is or what it is used for. In other words, the person lacks object recognition. People with this condition have no structural or neurological damage to the eye, nor is there any erosion in their intelligence that would explain the failure of object recognition. The problem behind this condition lies in the processing of visual information within the brain. There are two types of visual agnosia, apperceptive agnosia and associative agnosia.
Apperceptive agnosia, also called visual space agnosia, is the inability to recognize one object and to distinguish between two similar objects. For example, if a shoe and glove are placed in front of someone with apperceptive agnosia, the patient would be unable to identify either object. He would not even be able to perceive that the two objects are very different. People afflicted with this condition cannot copy a picture, play a matching game, or even complete a comparison test. This form of agnosia is most often caused by anoxia or prolonged depleted oxygen levels, stroke, or carbon monoxide poisoning.
There are three parts to visual associative agnosia. First, people with this type of agnosia can perceive an object using touch, or they will understand the object if it is described to them. In other words, they can identify the object using memory or any other sense other than sight.
Second, people with the condition may match similar objects but will not understand the function of the objects or even know their names. Finally, a patient with associative agnosia retains sufficient visual memory to be able to copy an image that she has seen. The causes of visual associative agnosia are highly variable, with lesions in many different areas of the brain resulting in this condition.
Visual agnosia was introduced to the public in Oliver Sacks’ book The Man Who Mistook His Wife for a Hat. Part of this book describes a man with visual agnosia who is highly functional in his professional and personal life despite his inability to recognize objects. This shows that people suffering from the condition are often able to compensate by relying on other senses, especially the sense of touch and smell. Clearly, object recognition is a complex function that relies heavily on the eyes and brain, but must also require input from all of the other senses for the brain to make a final decision. As of 2011, there is no therapy to cure this disease.
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