On Silhouettes, surfaces, and Sorensen

Sorensen (2008) argued that when we see a silhouetted object, the part of the object that we see is its back surface. I argue against this claim and in favour of the thesis that the part of a silhouetted object that we see is its edge/edges. I provide a general 'Parts Perception Principle' (PPP) for determining which part/parts of a seen object are seen and show that it both provides the intuitively correct answers in cases of normal seeing and also that it favours the edge theory over the back-side-theory in cases of seeing silhouetted objects. I also briefly compare and contrast cases in which a subject can see part of a camouflaged object.