An outline description is given of the experimental work on the visual acuity and hyperacuity of human beings. The very high resolution achieved in hyperacuity corresponds to a fraction of the spacing between adjacent cones in the fovea. We briefly outline a computational theory of early vision, according to which (a) retinal image is filtered through a set of approximately bandpass, spatial filters and (b) zero-crossings may contain sufficient information for much of the subsequent processing. Consideration of the optimum filter lead to one which is equivalent to a cell with a particular center-surround type of response. An "edge" in the visual field then corresponds to a line of zero-crossings in the filtered image. The mathematics of sampling and of Logan's zero-crossing theorem are briefly explained.
