The visual field representation in striate cortex of the macaque monkey: asymmetries, anisotropies, and individual variability.

The topographic organization of striate cortex in the macaque was studied using physiological recording techniques. Results were displayed on two-dimensional maps of the cortex, which facilitated the quantitative analysis of various features of the visual representation. The representation was found to be asymmetric with more cortex devoted to lower than to upper fields. Over much of striate cortex the representation is anisotropic, in that the magnification factor depends upon the direction along which it is measured. There is considerable individual variability in these features as well as in the overall size of striate cortex. Outside the fovea, the cortical representation shows only modest deviations from a logarithmic conformal mapping, in which the magnification factor is proportional to the inverse of eccentricity in the visual field. Comparison of receptive field size with cortical magnification was used to estimate the "point image size" in the cortex (i.e. the extent of cortex concerned with processing inputs from any given point in the visual field). Our evidence supports a previous report that point-image size varies significantly with eccentricity. This is of interest in relation to anatomical evidence that the dimensions of columnar systems in striate cortex are largely independent of eccentricity.