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Brainard, D.

Publications and source records attributed to Brainard, D..

3 recordsLinked to original sources

The relative contribution of color and material in object selection

Information about color, material, texture and shape guide how we interact with objects. We developed a paradigm that quantifies how two object properties (color and material) combine in object selection. On each experimental trial, observers viewed three blob-shaped objects -- the target and two tests -- and selected the test that was more similar to the target. Across trials the target was fixed while the tests varied in color and material. We present a novel observer model that allows us to describe observers selection data in terms of (1) the underlying perceptual stimulus representation and (2) a color-material weight, which quantifies the relative importance of color vs. material in selection. We document large individual differences in the color-material weight. Furthermore, our analyses reveal limits on how precisely selection data simultaneously constrain perceptual representations and the color-material weight. These limits should guide future efforts towards understanding the multidimensional nature of object perception.

neuroscience

Computational-Observer Analysis of Illumination Discrimination

The spectral properties of the ambient illumination provide useful information about time of day and weather. We study the perceptual representation of illumination by analyzing measurements of how well people discriminate between illuminations across scene configurations. More specifically, we compare human performance to a computational-observer analysis that evaluates the information available in the isomerizations of the cones in a model human photoreceptor mosaic. Some patterns of human performance are predicted by the computational observer, other aspects are not. The analysis clarifies which aspects of performance require additional explanation in terms of the action of visual mechanisms beyond the isomerization of light by the cones.

neuroscience

Simulating retinal encoding: factors influencing Vernier acuity

Humans resolve the spatial alignment between two visual stimuli at a resolution that is substantially finer than the spacing between the foveal cones. In this paper, we analyze the factors that limit the information at the cone photoreceptors that is available to make these acuity judgments (Vernier acuity). We use open-source software, ISETBIO1 to quantify the stimulus and encoding stages in the front-end of the human visual system, starting with a description of the stimulus spectral radiance and a computational model that includes the physiological optics, inert ocular pigments, eye movements, photoreceptor sampling and absorptions. The simulations suggest that the visual system extracts the information available within the spatiotemporal pattern of photoreceptor absorptions within a small spatial (0.12 deg) and temporal (200 ms) regime. At typical display luminance levels, the variance arising from the Poisson absorptions and small eye movements (tremors and microsaccades) both appear to be critical limiting factors for Vernier acuity.

neuroscience