The organization of the second visual area (V II) in the owl monkey: a second order transformation of the visual hemifield.

The visuotopic organization of the second visual area (V II) in the owl monkey was mapped by determining the receptive field positions for single neurons and small clusters of neurons recorded with microelectrodes. Our data indicate that V II is a long narrow strip of cortex which appears to correspond to area 18 of BrodmannB• The results also indicate that the topological transformation of the visual field in V II is fundamentally different from that in the primary visual area (V I). In V I, adjacent loci in the contralateral half of the visual field are always represented in adjacent cortical loci, and thus V I is a simple topological representation which we refer to as a first order transformation of the visual hemifield. In contrast, adjacent loci in the contralateral hemifield are not always represented in adjacent loci in V II. Beyond the central 7° in V II, the representation of the horizontal meridian splits to form most of the anterior border of V II, and the upper and lower quadrants of the visual field are represented separately. Thus, two adjoining parts of the visual field on each side of the horizontal meridian can be represented in quite separate parts of V II. We refer to V II as a second order transformation of the visual hemifield and sug­ gest that V II serves as a functional adjunct to V I.