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Biomedical subjects

J I Yellott

Publications and source records attributed to J I Yellott.

7 recordsLinked to original sources
PubMed1987

Photon noise and constant-volume operators.

In an earlier paper [J. Opt. Soc. Am. A 2, 1769 (1985)] a class of nonlinear image processing operators was introduced in which each photoreceptor creates a nonnegative point-spread function whose center height is proportional to its quantum catch and whose volume is constant, so that the local spatial-summation area varies inversely with the local quantum catch. These constant-volume (CV) operators are designed to maximize spatial resolution in the presence of photon noise. In the previous paper it was shown that when CV operators are applied to deterministic images, they produce a surprising range of effects that are reminiscent of human vision, including Mach bands and Weber's-law behavior. In this paper the consequences of applying CV operators to images containing Poisson noise are analyzed. It is shown that a fixed-parameter CV operator can duplicate the global qualitative properties of spatial vision for retinal illuminances ranging from absolute threshold to 1000 Td. Although there are fundamental obstacles to modeling the exact quantitative properties of human spatial vision by CV operators, these operators seem likely to be useful in machine vision.

Humans↗
PubMed1985

Intensity-dependent spatial summation.

Psychophysical evidence indicates that, in the human retina, the size of the spatial-summation area decreases as illuminance increases. Such a relationship would be beneficial for the detection of spatial contrast in the presence of photon noise. We analyze an image-processing mechanism in which the area of a strictly positive point-spread function varies inversely with local illuminance while its volume remains constant. In addition to its expected effect of improving spatial resolution as illuminance increases, this mechanism also yields center-surround antagonism and all other manifestations of bandpass filtering and accounts for Ricco's law and Weber's law--including the failures of both laws as a function of test conditions. The relationship between this mechanism and lateral inhibition is analyzed.

Humans↗
PubMed1984

Image sampling properties of photoreceptors: a reply to Miller and Bernard.

Miller and Bernard argue that photoreceptor sampling occurs at the inner rather than outer segments. Foveal inner segments form a lattice-like array that should create visible Moiré patterns when frequencies above 60 c/deg are image by interferometry. Despite a checkered past, this prediction is confirmed by recent experiments. Extrafoveally, frequencies above the nominal Nyquist limits of the cones are routinely present in the retinal image. Spectral analysis shows that the inner segments there form optimally irregular sampling arrays that avoid Moiré distortion by scattering supra-Nyquist frequencies into broadband noise. Thus is appears that topological disorder in the receptor mosaic prevents aliasing outside the fovea--the only place it could occur in normal vision.

Animals↗
PubMed1983

Spectral consequences of photoreceptor sampling in the rhesus retina.

Optical transforms were used to compute the power spectra of rhesus cones treated as arrays of image sampling points. Spectra were obtained for the central fovea, parafovea, periphery, and far periphery. All were consistent with a novel spatial sampling principle that introduces minimal noise for spatial frequencies below the Nyquist limits implied by local receptor densities, while frequencies above the nominal Nyquist limits are not converted into conspicuous moiré patterns, but instead are scattered into broadband noise. This sampling scheme allows the visual system to escape aliasing distortion despite a large mismatch between retinal image bandwidth and the Nyquist limits implied by extrafoveal cone densities.

Animals↗
PubMed1979

Depth inversion despite stereopsis: the appearance of random-dot stereograms on surfaces seen in reverse perspective.

Inside-out relief masks of faces can be depth-inverted (i.e. seen in reverse perspective) during close-up binocular viewing. If a random-dot stereogram is projected onto such a mask, stereopsis can be achieved for the stereogram, and its depth planes are correctly seen while the mask itself, including the region covered by the stereogram, is simultaneously perceived as depth-inverted. This demonstration shows that binocular depth inversion cannot be explained by a complete loss of stereoscopic information (e.g. through monocular suppression), or by a process analogous to pseudoscopic viewing whereby retinal disparities are incorporated into perception, but with their signs uniformly reversed.

Cues↗