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M A Finkelstein

Publications and source records attributed to M A Finkelstein.

6 recordsLinked to original sources
PubMed1990

Sites of sensitivity control within a long-wavelength cone pathway.

A flashed-field increment threshold paradigm was used to examine sites of sensitivity control within a long-wavelength cone pathway. The data were fit with a model containing two static nonlinearities, one at the receptors and the second at a red/green opponent stage. The nonlinearities are modified by multiplicative and subtractive processes of adaptation. Comparisons of the model's parameters with physiological measures of the long-wavelength cones suggest that, in the dark, sensitivity is controlled by the opponent site. At high adapting intensities, receptor nonlinearities may limit sensitivity under some conditions. The data also suggest that the spectral tuning of the opponent site varies with adapting intensity.

Color Perception↗
PubMed1984

Detection and discrimination of small, brief lights: variable tuning of opponent channels.

There is disagreement as to how closely the properties of the pathways that detect small spots resemble the properties of the achromatic system. Spectral sensitivities for small, brief lights show a single, relatively broadband peak similar to the achromatic spectral sensitivity. The lights also appear relatively desaturated near threshold. However, recent field sensitivity data (Finkelstein and Hood, 1981, 1982) have shown that opponent mechanisms are either directly involved in detecting small spots, or they interact with, and desensitize mechanisms are either directly involved in detecting small spots, or they interact with, and desensitize, a strictly achromatic detection pathway. The test sensitivity, test mixture, and wavelength discrimination data of the present study support the first alternative; they implicate opponent (chromatic) mechanisms in the detection of small, brief lights. However, the data cannot be fit by the same opponent systems used to fit large-test data. They suggest instead an hypothesis in which large and small lights are detected by opponent mechanisms that change their spectral tuning with changes in stimulus parameters.

Color Perception↗
PubMed1982

Opponent-color cells can influence detection of small, brief lights.

Spectral sensitivities for small, brief lights presented on a neutral adapting field resemble the photopic luminosity function. The lights often appear achromatic near threshold. These findings are consistent with a hypothesis linking sensitivity to an independent class of nonopponent cells. To test this hypothesis, a variation of the Stiles two-color threshold procedure was used. Field sensitivities were measured with a small, brief 580 nm target presented on flashed fields of monochromatic light; a 633/541 nm flash mixture was also used. All stimuli were delivered on a 4.0 log td steady neutral adapting field. The field sensitivity and field mixture data refute the hypothesis. They argue instead that reg/green opponent cells can substantially influence the detectability of small, brief lights.

Color Perception↗
PubMed1979

Comparison of changes in sensitivity and sensation: implications for the response-intensity function of the human photopic system.

Brightness magnitude estimations of foveally presented flashes deviate from a power function. Increment threshold functions for test lights presented upon these same flashes deviate drastically from a constant Weber fraction. These departures from the classic laws of sensation and sensitivity are shown to be in qualitative agreement and to be affected in similar ways by changes in steady adapting fields. Both sets of data can be fit over the lower range of flash intensities by models based on a saturating response function; both sets deviate from these models at high flash intensities in ways consistent with a nonsaturating response function.

Adaptation, Ocular↗