I agree. It's all dependent on what your brain sees first. It so happens that the absence of visual detail makes it easier to decide the mask as seen from the f

I agree. It's all dependent on what your brain sees first. It so happens that the absence of visual detail makes it easier to decide the mask as seen from the front instead of from the back. The moment your brain is told that it should not be seeing the concave face a switch turns on telling you how to 'see' the mask.