Importance of hue: color discrimination of three-dimensional objects and two-dimensional discs

While flat, 2D stimuli have traditionally been used to measure color discrimination, our everyday interactions typically involve 3D objects. Here, we compare discrimination thresholds for rendered matte 3D objects and uniform discs. Participants performed a 4AFC odd-one-out task, where the odd stimulus reflectance differed in hue or chroma in four quadrants of DKL color space. Hue thresholds for 3D objects and 2D discs were equal, while object chroma thresholds were significantly higher, suggesting that hue is especially important for object discrimination. Chroma-to-hue threshold ratios were above 1 in all quadrants, particularly the bluish and orangish where a preponderance of natural object reflectances plot. This supports the idea that hue is also more important for the object colors we see most in our environment.