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Recent neuroscientific studies on the cerebral mechanism of vision in animals and man have revealed that modular organization is the basic principle underlying visual information processing in the brain (Ungerleider and Mishkin, 1982; Macko et al., 1982: Macko and Mishkin, 1985; Iwata, 1989; Zeki, 1992). That is to say, the brain consists of a number of independent computers, each one of which is specialized for analyzing a special feature of the visual information coming from the outside world. Each individual special feature of the information to be analyzed separately is called a “module,” and the system of such division of labor is called “modular organization” (Marr, 1982). Table 1 shows the modules that are known to be processed by a certain specific cortical area.
Experimental physiologists divided various cortical areas related to vision into five areas named V1, V2, V3, V4, and V5. V1 is the primary visual cortex; V2, V3, and V4 are visual association areas; and V5 belongs to the higher association areas (Van Essen and Maunsell, 1980; Livingston and Hubel, 1988; Zeki, 1992).
V1 consists of three different functional units: an orientation column that detects the spatial orientation of lines; a color blob that reacts to color; and layer 4B, which is sensitive to the motion of lines.
V2 consists of three different stripes arranged in alternation; these can be differentiated by cytochrome oxidase staining into thin stripes, thick stripes, and interstripes. Thin stripes have input mainly from the color blobs of V1 and send their outputs to V4. V4 is thought to be the analyzer of color. The neurons of the color blobs of V1 and of the thin stripes of V2 selectively react to the wavelength of the input, while in V4, there are color-coded neurons that