Shape-from-shading depends on visual, gravitational, and body-orientation cues.

@article{Jenkin2004ShapefromshadingDO,
  title={Shape-from-shading depends on visual, gravitational, and body-orientation cues.},
  author={H. L. Jenkin and Michael R. M. Jenkin and Richard Dyde and Laurence R. Harris},
  journal={Perception},
  year={2004},
  volume={33 12},
  pages={1453-61}
}
The perception of shading-defined form results from an interaction between shading cues and the frames of reference within which those cues are interpreted. In the absence of a clear source of illumination, the definition of 'up' becomes critical to deducing the perceived shape from a particular pattern of shading. In our experiments, twelve subjects adjusted the orientation of a planar disc painted with a linear luminance gradient from one side to the other, until the disc appeared maximally… CONTINUE READING