Lighting direction and visual field modulate the brightness of 3D objects M McCourt, B Blakeslee, G Padmanabhan |
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Center for Visual and Cognitive Neuroscience, North Dakota State University, ND, United States
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| When interpreting object shape the visual system assumes that illumination comes from above left. Does the direction of lighting influence object brightness (and/or perceived intensity of illumination)? An array of nine cubes was stereoscopically rendered. Individual cubes varied in their 3D pose, but all possessed identical triplets of visible faces. The cubes were illuminated from one of four directions: above-left, above-right, below-left, and below-right (±24.4o; ±90o). Simulated illumination intensity possessed 15 linear levels. “Standard” cubes were illuminated from above-left at intensity 8; comparison cubes were illuminated from the four directions and appeared in either the left or right visual field. Using the method of adjustment we determined comparison cube illumination required to establish subjective equality with the standard cubes as a function of comparison cube visual field, illumination elevation, and illumination azimuth. Cubes appeared significantly brighter in the left visual field (p=.008), and when illuminated from below (p<.001). The enhanced brightness of cubes lit from below was greatest when also lit from the right (p=.001). Cubes lit from below appear brighter (more highly illuminated) than identical cubes lit from above, due perhaps to long-term adaptation to downward lighting. Brightness is amplified in the left visual field, presumably via attentional enhancement. |
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