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F E Cheney

Publications and source records attributed to F E Cheney.

6 recordsLinked to original sources
PubMed1993

Probability-summation model of multiple laser-exposure effects.

A probability-summation model is introduced to provide quantitative criteria for discriminating independent from interactive effects of multiple laser exposures on biological tissue. Data that differ statistically from predictions of the probability-summation model indicate the action of sensitizing (synergistic/positive) or desensitizing (hardening/negative) biophysical interactions. Interactions are indicated when response probabilities vary with changes in the spatial or temporal separation of exposures. In the absence of interactions, probability-summation parsimoniously accounts for "cumulative" effects. Data analyzed using the probability-summation model show instances of both sensitization and desensitization of retinal tissue by laser exposures. Other results are shown to be consistent with probability-summation. The relevance of the probability-summation model to previous laser-bioeffects studies, models, and safety standards is discussed and an appeal is made for improved empirical estimates of response probabilities for single exposures.

Humans↗
PubMed1987

Vision beyond the resolution limit: aliasing in the periphery.

Pattern resolution is generally considered a prerequisite for spatial vision because details too fine to be resolved cannot be distinguished from a uniform field. However, our experiments using peripheral vision demonstrate that reliable pattern detection is possible for images far beyond the resolution limit. The visual percept which arises in this case is an illusion called aliasing in which the apparent spatial structure of the stimulus is quite different from that actually present. Aliasing begins at spatial frequencies just above the classical resolution limit, which is taken as evidence that peripheral resolution is limited by the coarse spacing of visual neurons rather than by increased size of their receptive fields. At a given eccentricity, the very finest pattern which produces aliasing has a spatial period which approaches the smallest anatomical dimension: the diameter of a single cone photoreceptor.

Form Perception↗
PubMed1987

Retinal limits to the detection and resolution of gratings.

The maximum spatial frequency for the detection and resolution of sinusoidal gratings was determined as a function of stimulus location across the visual field. Stimuli were produced directly on the retina as interference fringes, thus avoiding possible loss of image quality, which may occur when the optical system of the eye is used to form the retinal image. Contrary to earlier reports, we found that subjects could detect gratings with spatial frequencies much higher than the resolution limit. At 5 degrees of eccentricity from the fovea, the detection limit was about three times the resolution limit, and this factor increased to about 10 as the test stimulus was moved 35 degrees into the periphery. Quantitative comparison of the data with retinal anatomy and physiology suggests that pattern resolution is limited by the spacing of primate beta (midget) retinal ganglion cells, whereas pattern detection is limited by the size of individual cones.

Humans↗