The incapacity to recognise objects, despite adequate sensory information about them reaching the brain via the ears or eyes or through touch. In order for an object to be recognised, the sensory information it provides must be interpreted, which involves the recall of memorised information about similar objects. Agnosia is caused by harm to areas of the brain involved in interpretative and recall functions. The most widespread causes of this kind of damage are head injury or stroke.
Agnosia is commonly associated with just one of the senses of vision, touch, or hearing and is described as visual, auditory, or tactile respectively. For example an object could be completely recognisable by touch and hearing, but it cannot be recognised by sight, despite the sense of vision being perfectly normal (an example of visual agnosia). Occasionally some people, after experiencing a stroke that damages the right cerebral hemisphere seem uninformed of any disability in the affected left limbs. This is called sensory inattention or agnosia.
There is no particular treatment for agnosia, but some of the lost interpretative ability may ultimately return.