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.
Associative visual agnosia
Teuber described the associative agnostic as having a "percept stripped of its meaning," because the afflicted individual cannot generate unique semantic information to identify the percept, since though it is fully formed, it fails to activate the semantic memory associated with the stimulus. Warrington (1975) offered that the problem lies in impaired access to generic engrams (memory traces) that describe categories of objects made up of a multitude of similar elements. Essentially, damage to a modality-specific meaning process (semantic system), is proposed, either in terms of defective access to or a degradation of semantic memory store for visual semantic representations themselves. The fact that agnosias are often restricted to impairments of particular types of stimuli, within distinct sensory modalities, suggests that there are separate modality specific pathways for the meaningful representation of objects and pictures, written material, familiar faces, and colors.