The studies reported in Annual Technical Report 1 were designed to probe various aspects of spatial pattern discrimination. Several important findings have emerged allowing limits of pattern discrimination to be related to structural properties of the photoreceptor lattice. First, our findings have suggested that spatial frequency discrimination exceeds resolution of the photoreceptor mosaic for spatial frequencies above approximately 4 c/deg, thus spatial frequency discrimination qualifies as a hyperacuity task. Further, spatial frequency discrimination was not a smooth function of spatial frequency, but rather showed a regularly segmented structure that appeared to be related to foveal photoreceptor center-to-center spacing. This result suggests that the photoreceptor lattice could be the primary geometrical instrument for estimating distance or separations between stimulus features. We have developed a technique to study the structural quality of a retinal mosaic by digitizing the foveal photoreceptor lattice of a primate (Macacca fascicularis). Our analyses of the foveal region has revealed a very high quality hexagonal lattice with a correlation length of at least 130 photoreceptors. These results confirm that the photoreceptor lattice is constructed with sufficient structural quality to provide a source of geometrical information reflected in spatial discrimination tasks.