The study of patients with lesions of the central visual system has shown that certain complex visual disturbances are generally associated with lesions in the ventral occipital lobe and adjoining temporal lobe, while other disturbances are more commonly associated with lesions of the dorsal occipital cortices and adjoining parietal lobe. Cerebrovascular lesions in the distribution of the posterior cerebral artery, tumor, trauma, and neurodegenerative processes such as Alzheimer's disease are common etiologies of these disturbances and can be assessed using modern neuroimaging techniques. The corresponding visual function deficits can be separated out by a systematic clinical approach incorporating visual sensory and cognitive testing procedures, as outlined below.