An 11-bit High Dynamic Range (HDR) Luminance Display and Its Use to Discover Contextual Mechanisms of Real-World Luminance Normalization for Visual Acuity and Target Discrimination
Chou P Hung,
Paul D Fedele,
Kim F Fluitt,
Barry D Vaughan,
Anthony J Walker,
Matthew M Jaswa,
Andre V Harrison
Posted 05 Aug 2019
bioRxiv DOI: 10.1101/718437
Posted 05 Aug 2019
Luminance can vary widely when scanning across a scene, by up to 10^9 to 1, requiring multiple normalizing mechanisms spanning from the retina to cortex to support visual acuity and recognition. Vision models based on standard dynamic range luminance contrast ratios below 100 to 1 have limited ability to generalize to real-world scenes with contrast ratios over 10,000 to 1 (high dynamic range [HDR]). Understanding and modeling brain mechanisms of HDR luminance normalization is thus important for military applications, including automatic target recognition, display tone mapping, and camouflage. Yet, computer display of HDR stimuli was until recently unavailable or impractical for research. Here we describe procedures for setup, calibration, and precision check of an HDR display system with over 100,000 to 1 luminance dynamic range (650-0.0065 cd/m^2), pseudo 11-bit grayscale precision, and 3-ms temporal precision in the MATLAB/Psychtoolbox software environment. The setup is synchronized with electroencephalography and IR eye-tracking measurements. We report measures of HDR visual acuity and the discovery of a novel phenomenon - that abrupt darkening (from 400 to 4 cd/m^2) engages contextual facilitation, distorting the perceived orientation of a high-contrast central target. Surprisingly, the facilitation effect depended on luminance similarity, contradicting both classic divisive and subtractive models of contextual normalization.
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