What causes agnosia?
Agnosia
In order to assess an individual for agnosia, it must be verified that the individual is not suffering from a loss of sensation, and that both their language abilities and intelligence are intact.  In order for an individual to be diagnosed with agnosia, they must only be experiencing a sensory deficit in a single modality.  To make a diagnosis, the distinction between apperceptive and associative agnosia must be made.  This distinction can be made by having the individual complete copying and matching tasks.  If the individual is suffering from a form of apperceptive agnosia they will not be able to match two stimuli that are identical in appearance.  In contrast, if an individual is suffering from a form of associative agnosia, they will not be able to match different examples of a stimulus.  For example, an individual who has been diagnosed with associative agnosia in the visual modality would not be able to match pictures of a laptop that is open with a laptop that is closed.[3]