Abstract

Contrast thresholds in foveal vision for circular disks of various angular sizes were measured as the image was blurred by being thrown out of focus. The threshold increased with blurring of the retinal image, but the rate of this increase was less with the larger stimulus disks. The data plot was fitted by an equation developed on theoretic bases, which used the concept of a minimal effective retinal area. The relationship between contrast threshold and size of the stimulus disk was shown to be described by a hyperbola, one asymptote of which was defined by Ricco’s law, the other by a constant threshold for larger subtenses of the disk. This relationship was shown to fit adequately the data of other investigators for sharp imagery. With blurring of imagery, the thresholds were increased; but below a critical angle, they obeyed Ricco’s law. The critical angle increased with increase of blurring. The results are discussed with regard to the optical image on the retina, quasi-independent retinal areas with total or partial summation, and the influence of experimental conditions.

© 1961 Optical Society of America

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Blurring of the Retinal Image and Contrast Thresholds in the Fovea*

Kenneth N. Ogle
J. Opt. Soc. Am. 50(4) 307-315 (1960)

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