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Toni Saarela, Maria Olkkonen; Integration of color and gloss in surface material discrimination. Journal of Vision 2017;17(10):229. doi: 10.1167/17.10.229.
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Background: Real-world surfaces differ from each other in several respects, for example, in roughness, diffuse reflectance (color), and specular reflectance (gloss). When identifying and discriminating surface materials, the visual system could use information from several such cues to perform more precisely and consistently across varying viewing conditions. We tested the integration of information from diffuse and specular reflectance in a discrimination task. Methods: Stimuli were spectrally rendered images of 3D shapes with surface corrugation. We independently varied two surface-material "cues": (1) diffuse reflectance, resulting in greenish-to-bluish color variation, and (2) specular reflectance, resulting in matte-to-glossy appearance variation. On each trial, the observer saw a reference and a test stimulus. The reference was near the middle of the color and gloss ranges, with trial-to-trial jitter. In different blocks of trials, the test varied in the color-only, gloss-only, or in one of three intermediate directions. The observer identified the bluer and/or glossier stimulus. We fit psychometric functions to the proportion-bluer/glossier data to estimate discrimination thresholds. To encourage observers to judge surface properties rather than local image cues, different shapes were interleaved, but within each trial the two shapes were identical. Each shape was further rendered with several rotation angles, changing the pattern of colors and specular highlights. On each trial, rotation was selected randomly for each stimulus. Results: Having two cues improved discrimination: Thresholds were lower in the two-cue, compared to the single-cue conditions. Comparison against model predictions revealed that cue integration was less than optimal statistically, falling between the optimal and strongest-single-cue threshold predictions. Conclusion: The visual system can combine information from color and gloss to improve discrimination of surface material, although the integration falls short of statistically optimal. When faced with shape, viewpoint, and material variation, the visual system might rely on a robust but sub-optimal strategy of cue integration.
Meeting abstract presented at VSS 2017
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