Morphologic and physiologic studies have identified many regions of the cerebral cortex that are involved in vision. All of these are, in some sense, “Visual cortex,” but this term also has more restricted meanings. “Primary visual cortex” refers to a region of distinctive cytoarchitecture that the anatomist Brodmann designated area 17. In primates, this is the principal target of the geniculo-cortical projection. Echoing this fact, as well as its appellation of primary visual cortex, area 17 is sometimes designated VI. The term “striate cortex” arises from the presence in humans of the stria of Gennari, a prominent horizontal band in area 17 that stains heavily for myelin and is visible to the naked eye in fresh tissue. It is also called the calcarine cortex because it lies adjacent to the calcarine sulcus. Visually responsive regions outside area 17 are collectively called extrastriate areas and will be treated later in this chapter.

Effects of Lesions in Striate Cortex

Humans with complete destruction of the striate cortex on one side cease to perceive stimuli in the contralateral visual field. Partial lesions result in localized scotomata, which may be more or less “dense” depending on how much function remains. Sometimes vision is reduced to detection of motion or the presence of light. When the striate cortex and nearby regions are ablated in nonhuman primates, severe deficits are observed in tasks that presumably require visual perception. Ablation of visual cortex in other animals does not always produce such striking deficits.