The neural representation of visual space

Abstract

THE approximate form of the projection of visual space on the striate cortex in man has long been established from neurological evidence^1–3 and estimates of cortical magnification M (the extent of striate cortex in millimetres corresponding to a degree of arc in visual space) have been derived from studies on cortical phosphenes and visual acuity⁴, and migraine scotoma dimensions⁵. The possibility that M could be estimated from the density of retinal ganglion cells which provide the output from the eye to the brain has received support from studies on monkeys^6–8. It has been shown that M is proportional to √D_c (where D_c is the projected ganglion cell density in cells per solid degree of visual space) for peripheral angles (θ) greater than 10°. More centrally, where D_c is maximal, this relationship breaks down because the cells are displaced from their receptive fields by an amount which is difficult to determine⁸. If data on ganglion cell receptive field density, D_r (in receptive fields per solid degree) were available, they might be expected to relate to M at every point in the visual field. I report here that I have obtained such estimates of D_r and examined their usefulness as predictors of M. The results are summarised in three basic equations.