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Qualitative shape from shading?

Experimental question (Todd and Reichel): is shape perception metric (depth), or ordinal (depth order)?

Prediction: If ordinal, judgement of relative depth between two points will be strongly affected by nonmonotonicity of the intervening surface.

Finding: it is.

Interpretation: in favor of qualitative rather than quantitative shape from shading.

Edelman Shimon
Wed Oct 18 09:18:18 EDT 1995