We measure the center-to-center spacings and disorder in spacings between all pairs of cones in a strip of primate retina extending from the foveal center to approximately 5.75 deg of retinal eccentricity along the temporal horizontal meridian. The strip is partitioned into windows, and the positions of the cone centers in each lattice window are digitized for analysis of lattice structure and quality. We find a nearly monotonic increase in cone spacing with eccentricity. The cone mosaic is a high-quality hexagonal lattice near the foveal center, and cone positional disorder (jitter) relative to averaging spacing increases beyond about 1.5 deg. We estimate human acuity measured through the optics of the eye over a retinal region comparable with our lattice strip by pooling the results of previous investigators. When the monkey lattice is scaled to human foveal resolution, application of the sampling theorem to average cone spacing predicts these pooled visual-acuity data from the foveal center to about 1.5 deg and overestimates visual acuity more eccentrically. Orientation reversal, a new technique developed by Coletta and Williams [
J. Opt. Soc. Am. 4,
1987)] for estimating the Nyquist limit, estimates Nyquist frequencies from the foveal edge to beyond 5 deg of retinal eccentricity that agree with the cutoff frequencies predicted on the basis of our average spacing measurements. We conclude that the sampling theorem based on average spacing alone predicts the Nyquist limit from the foveal center to about 5 deg when that limit is measured by using the new aliasing technique. The sampling theorem based on average spacing overestimates the pooled estimate of visual acuity from the foveal edge to about 5 deg, probably because of sampling noise caused. by orientation and spacing disorder combined with demodulation as a result of the optics of the eye.
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