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We have studied the ability of observers to discriminate between suprathreshold vertical sinusoidal spatial-frequency gratings on the basis of spatial frequency. The results show that spatial-frequency discrimination is not a smooth function of spatial frequency but instead appears regularly segmented. Similar results were also obtained in an experiment in(More)
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(More)
We test the hypothesis that the diameters of foveal and near-foveal rods and cones for one well-studied human photoreceptor mosaic and one well-studied monkey photoreceptor mosaic (Macaca fascicularis) are scaled relative to focal length. We conclude that this hypothesis is not supported. Rather than being scaled proportionally, the sizes of the rods and(More)
Pseudohyphal differentiation in the budding yeast Saccharomyces cerevisiae is induced in diploid cells in response to nitrogen starvation and abundant fermentable carbon source. Filamentous growth requires at least two signaling pathways: the pheromone responsive MAP kinase cascade and the Gpa2p-cAMP-PKA signaling pathway. Recent studies have established a(More)
Regulatory genes directing embryonic development are expressed in complex patterns. The Drosophila homeobox gene fushi tarazu (ftz) is expressed in a striped pattern that is controlled by several discrete and large cis- regulatory elements. One key cis-element is the ftz proximal enhancer which is required for stripe establishment and which mediates(More)
We test three specific models of how the human visual system computes a just-noticeable-difference (jnd) in spatial separation. The strategies employed by these three models range from strictly local to global, and use a new discrimination task that measures the precision with which displacements of random dots in random dot arrays can be detected. Fits of(More)
Quantitative analysis of a primate photoreceptor lattice shows that the foveal lattice is a highly regular hexagonal structure with a positional correlation length of at least 130 photoreceptors. This result indicates that the photoreceptor lattice is not sufficiently disordered to prevent aliasing in the fovea, but rather could provide the metric with(More)
The yeast mer1 mutant produces inviable spores and is defective in both meiotic recombination and chromosome pairing. A gene called MER2 partially suppresses the mer1 phenotype when present in high copy number. Both gene conversion and chromosome pairing are completely restored in mer1 strains overexpressing MER2; however, reciprocal crossing over and spore(More)
The large subunit of RNA polymerase II contains a highly conserved and essential heptapeptide repeat (Pro-Thr-Ser-Pro-Ser-Tyr-Ser) at its carboxy terminus. Saccharomyces cerevisiae cells are inviable if their RNA polymerase II large subunit genes encode fewer than 10 complete heptapeptide repeats; if they encode 10 to 12 complete repeats cells are(More)