Spatial frequency representation in V2 and V4 of macaque monkey
Spatial frequency (SF) is an important attribute in the visual scene and is a defining feature of visual processing channels. However there remains many unsolved questions about how primate visual cortex, in particular extrastriate areas V2 and V4, codes this fundamental information. Here, using intrinsic signal optical imaging in visual cortex of Macaque monkeys, we quantify the relationship between spatial frequency maps and (1) visual topography, (2) color and orientation maps, and (3) across visual areas V1, V2, and V4. We find that in orientation regions, low to high spatial frequency is mapped orthogonally to orientation; however, in color regions, which is reported to contain orthogonal axes of color and lightness, only low spatial frequencies are represented without a gradient of SF representation. This produces the first observation of a population spatial frequency fluctuation related to the repeating color/orientation organizations. These findings support a generalized hypercolumn model across cortical areas, comprised of two orthogonal parameters with additional parameters.