Agnosia
Agnosia is the inability to process sensory information. Often there 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. It is usually associated with brain injury or neurological illness, particularly after damage to the occipitotemporal border, which is part of the ventral stream. Agnosia only affects a single modality, such as vision or hearing. More recently, a top-down interruption is considered to cause the disturbance of handling perceptual information.
Associative visual agnosia
Visual object agnosia (or semantic agnosia) is the most commonly encountered form of agnosia. The clinical "definition" of the disorder is when an affected person is able to copy/draw things that they cannot recognize. Individuals afflicted with the associative type often cannot identify, describe or mimic functions of items, though perception is intact, since images of objects can be copied or drawn. Individuals may retain semantic knowledge of the items, as exemplified during tasks where objects are presented through alternate modalities, through touch or verbal naming or description. Some associative visual object agnostics retain the ability to categorize items by context or general category, though unable to name or describe them. Diffuse hypoxic damage is the most common cause of visual object agnosias.