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Yury Petrov, Jiehui Qian; Optic flow strongly affects brightness. Journal of Vision 2010;10(7):418. doi: 10.1167/10.7.418.
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It is well known that brightness/lightness is determined by the pattern of luminance within the target's context. Here we report a new phenomenon demonstrating that brightness is also strongly affected by the motion pattern within the context. We found that the optic flow of dots which is consistent with the dots moving in depth modulates their brightness. The brightness of light dots increases while the brightness of dark dots decreases by 30% when the dots appear to move away to twice the original distance from the viewer. The effect reverses when the dots appear to move nearer. The effect persists for a wide range of dot contrasts, velocities, sizes, densities, and background luminances. We also found that the density of dots modulates their brightness in a similar fashion, but the density effect alone is about 3 times weaker than that produced by the optic flow. To explain the phenomenon we suggest that the brain calculates brightness based on the estimated distance to the dots. When the distance appears to increase while the luminance of the dots remains constant, the brain interprets this as an increase in the dots' luminosity and (partially) displays this increased luminosity as the increased brightness. This interpretation is corroborated by the fact that the size of the dots appears to be modulated in the same fashion as their brightness: the receding dots seem to grow, while the approaching dots seem to shrink.
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