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Final Technical Report on Contract FQ8671-83-0517 for 1 February 1983 - 31 January 1986,
EYE RESEARCH INST OF RETINA FOUNDATION BOSTON MA
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Low contrast, low spatial frequency luminance sawtooth patterns look like luminance staircases, with no brightness changes over the shallower luminance slope. Brightness measurements at corresponding points in different cycles of these patterns showed substantial illusory brightness differences. Other measurements showed that the illusion is not confined to strictly subthreshold luminance gradients, but occur with slightly suprathreshold gradients as well. In models which attempt to explain these visual illusions the visual system integrates over the thresholded gradient of the stimulus distribution. The integration encounters problems due to curl introduced by the nonlinear threshold operator. Lightness measurements indicated that these problems have a visual counterpart, further support for the models. Several new illusion were found to result from this nonlinear threshold for spatial gradient, including patterns where gradients were perceived in uniform regions and nonuniform stimulus regions were perceived as uniform. Color constancy was measured for multiple regions of the visual field under different illuminants.
APPROVED FOR PUBLIC RELEASE