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
Most cases have injury to the occipital and temporal lobes and the critical site of injury appears to be in the left occipito-temporal region, often with involvement of the splenium of the corpus callosum. The etiology of the cognitive impairment, as well the areas of the brain affected by lesions and stage of recovery are the primary determinants of the pattern of deficit. More generalized recognition impairments, such as, animate object deficits, are associated with diffuse hypoxic damage, like carbon monoxide poisoning; more selective deficits are correlated with more isolated damage due to focal stroke.