Given the absence of a highly detailed model, in this case a Charlie Chaplain mask, the illusory effects may be due to the absence of sufficient visual depth cues - similar to the effects seen in the "Spinning Dancer" effect. As a further example, next time you see a plane in the air making a turn at a great distance from you, there are actually two ways you could perceive its direction - all dependant on what you convince your brain it to be first. I would not draw too many conclusions from such a vague study.
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.
