Disorder of higher visual function

Both monkey and human neuroimaging studies show that visual processing beyond the striate cortex involves a highly complex network of regions with modular functions. Lesions within this network lead to specific clinical syndromes. In this review we discuss studies on blindsight, which is the ability of remaining regions to support vision in the absence of striate cortex or visual awareness, recent work on 'ventral stream' syndromes such as object agnosia, alexia, prosopagnosia, and topographagnosia, which follow damage to medial occipitotemporal structures, and simultanagnosia, the classic 'dorsal stream' deficit related to bilateral occipitoparietal lesions.

We highlight work on the anatomic basis of blindsight, the recent description of the new disorder developmental topographic disorientation, and studies contrasting global and local perception in simultanagnosia.

These studies advance our understanding of the mechanisms of complex visual processing and provide an important neuropsychological complement to our expanding knowledge about vision from functional neuroimaging.