Abstract
Two principles in neuronal organization are pivotal to the understanding of visual cortical processing: multiple parallel pathways and anatomical segregation of functionally specialized areas. The functional specialization of separate anatomical areas is confirmed by the effect of selected lesions producing deficits limited to color, spatial perception, or movement. It must be acknowledged that anatomical segregation is far from absolute and some lesions limited to specific areas only produce a temporary effect with subsequent recovery. Anatomical studies in primates have demonstrated 305 interconnecting pathways among the various visual areas. Question remains on the reconciliation of the hypotheses of multiple parallel channels, functional specialization, and hierarchical organization with the unitary integrated phenomenology of visual experience. The hypothesis of a distributed network may bring these separate concepts together. The visual system is modular; modules are added as needed to increase information processing and each module operates via a distributed network with crucial nodal points (or information bottlenecks). The most crucial nodal point is VI where all incoming information is received and then distributed to the other areas of the network. Lesions at crucial nodal points are likely to produce specific visual deficits for example, homonymous hemianopia in VI lesions. Lesions in the network may be silent or transient. Other modules or network connections may compensate for the damaged area (plasticity).