A diamond pattern, first noticed in 1995 in the Vision Lab, produces a cumulative lightness effect. The well known Cornsweet edge creates the perception of a single step in surface lightness between two adjacent regions even though they have identical mean luminance. We might imagine that a concatenated set of these Cornsweet edges would create accumulating lightness steps, but they do not. The diamond pattern, with each diamond filled with an identical luminance gradient does give a cumulative Cornsweet effect (Cavanagh & Anstis, 2018, PDF). These effects are consistent with an illumination gradient interpretation: a set of diamonds each of uniform lightness but stepping up in lightness from left to right viewed under an illuminant that decreases from left to right. It turns out that the key is to have the illumination change along the edges to strengthen the effect. The effect is more evident for the pointy diamonds on the left than for the squat diamonds on the right.
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