Visual agnosia is a rare neuropsychological disorder which may affect the processing of object form, integration of object parts or access to the meaning of a perceived shape. These distinct stages of object processing are the presumed levels of impairment that characterize form, integrative and object agnosia respectively. In contrast to these three disorders simultanagnosia can be described as a disorder of attention, rather than perception. Patients with this disorder suffer from a severe restriction of spatial attention, sometimes resulting in the impossibility to perceive more than one object at a time. Thorough study of patients with visual agnosia provides invaluable clues about the cognitive and neural architecture of object processing.