Shape Constancy

When an objects shape changes depending on the angle we view it at even though the actual size cannot change is called shape constancy. Its when we perceive the form of familiar objects as constant even while out retinal images of them change. For example the CD below looks thin in the top left picture, but then in the one next to that the CD looks wider. Finally in the bottom picture the full surface o the CD is shown and it seems to have a different shape compared to the other two when really it doesn't; its just the angle of the camera that distorts our vision of seeing the whole CD.