Why the cortical magnification factor in rhesus can not be isotropic.

Using the data of Hubel and Wiesel (1974) J. comp. Neurol. 158, 295-306, on macaque, the shape of the operculum of striate cortex (area 17) is calculated from their magnification factor values assuming that the cortical magnification factor is locally isotropic with respect to displacement on the cortical surface (from a fixed point of origin). Using geometric considerations, the shape predicted from the isotropic assumption is inconsistent with the actual shape given by anatomical reconstruction by LeVay, Hubel and Wiesel (1975) J. comp. Neurol. 159, 559-576. Rather the true shape is more consistent with the hypothesis that on the average the magnification factor along a meridian is twice the value as orthogonal to it. Except in the region of the horizontal meridian, this is often the same as assuming that the magnification factor across ocular dominance columns is twice that going parallel to them.