Contrast dependency of foveal spatial functions: orientation, vernier, 
separation, blur and displacement discrimination and the tilt and Poggendorff 
illusions

Westheimer, G; Brincat, S; Wehrhahn, C

doi:10.1016/S0042-6989(98)00200-4

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Contrast dependency of foveal spatial functions: orientation, vernier, separation, blur and displacement discrimination and the tilt and Poggendorff illusions

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Wehrhahn, C
Department Physiology of Cognitive Processes, Max Planck Institute for Biological Cybernetics, Max Planck Society;
Max Planck Institute for Biological Cybernetics, Max Planck Society;

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https://www.sciencedirect.com/science/article/pii/S0042698998002004
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Citation

Westheimer, G., Brincat, S., & Wehrhahn, C. (1999). Contrast dependency of foveal spatial functions: orientation, vernier, separation, blur and displacement discrimination and the tilt and Poggendorff illusions. Vision Research, 39(9), 1631-1639. doi:10.1016/S0042-6989(98)00200-4.

Cite as: https://hdl.handle.net/11858/00-001M-0000-0013-E721-1

Abstract

To examine the effect of reducing luminance contrast in human foveal vision, discrimination thresholds were measured in four tasks and also a
numerical measure of two visual illusions were obtained by a nulling technique. The patterns used for all tasks were made very similar to facilitate comparison
between them-all featured luminance step edges whose contrast could be varied from near unity down to the detection threshold. Orientation, vernier and blur
discrimination thresholds rise on average 5-6-fold when the contrast is reduced from near unity to a Michelson value of 0.03. Jump displacement thresholds are
somewhat more robust to contrast reduction, and the curve of separation discrimination versus contrast is much shallower, rising by a factor of about 2. The
magnitude of the Poggendorff and tilt illusions changes very little until the inducing contours are barely detectable. (C) 1999 Elsevier Science Ltd. All rights
reserved.