Magnification factors and the organization of the human striate cortex.

We review the evidence relating to the organization of the human striate cortex to determine whether the latter is organized in a way similar to that of the macaque monkey. There are only limited data available to allow direct determination of the magnification factors in human striate cortex. These suggest that the linear magnification factor is about 1.6 times greater than that in the macaque. This is consistent with the observations that the human striate cortex, compared to that of the macaque, has over 2 times the area, has neurones with longer dendrites, wider ocular dominance columns and more widely separated cytochrome oxidase "blobs". The striate cortices in both species have the same total number of neurones. The foveal magnification factor in the macaque is presently believed to be about 15 mm.deg-1; it seems reasonable, therefore, to believe that the human foveal value will be about 20-25 mm.deg-1 rather than the value of 8-11 mm.deg-1 which is currently accepted. Magnification factor falls more rapidly with eccentricity than do current estimates.