Apperceptive agnosia
Each patient that suffers from apperceptive agnosia does not have brain damage in exactly the same area. However, brain damage in proximity to the occipital lobe is largely correlated with the patterns of deficit seen in apperceptive agnosics. For example, patient JB suffered extensive damage to the parietal-occipital areas to the left cerebral hemisphere leading to his deficit in the ability to name distinguish between structurally similar object.
Apperceptive agnosia
Visual apperceptive agnosia is a visual impairment that results in a patient's inability to name objects. While agnosics suffer from severe deficits, patients' visual acuity and other visual abilities such as perceiving parts and colours remain intact. Deficits seem to occur because of damage to early-level perceptual processing. While patients are able to effectively allocate attention to locate the object and perceive the parts, they are unable to group together the parts they see and name the object accurately. This is demonstrated by the fact that patients are more effective at naming two attributes from a single object than they are able to name one attribute on each of the two superimposed objects. In addition they are still able to describe objects in detail and recognize objects by touch.