The organization of sensory cortex.

Recent studies of primary visual cortex (V1) redefine layers 3 and 4 of V1 in monkeys and show that monkeys, apes and humans have different laminar specializations. Projections from V1 define a smaller, but complete, third visual area, and a dorsomedial area. The middle temporal visual area has two types of motion-sensitive modules with inputs from cytochrome oxidase columns in V1. Second-level somatosensory areas have been described in humans, and a second-level auditory area is shown to respond to somatosensory stimuli.