Active manipulation of surface orientation under directional illumination improves color discrimination

Human observers show improved surface color discrimination when they can actively tilt surfaces to sample directional illumination, confirming directional variation helps overcome illuminant metamerism.

• Why it matters: Illuminant metamerism can make two differently colored surfaces look the same under a fixed, directionally uniform light, limiting discrimination. Real lighting varies by direction, but whether observers can exploit that variation was unclear.
• What they did: The study tested human observers under directional illumination while allowing spatiotemporally structured surface tilting to change the sampled illumination spectrum. Observers’ sampling motions were analyzed for how they related to lighting geometry versus pair-specific color cues.
• The result: Discrimination improved with tilting, and motion patterns appeared directed toward the general lighting geometry rather than systematically maximizing information for specific surface pairs. This implies directional sampling can be used to reduce metamerism-related confusion.

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