Size-constancy effects make distant objects, especially in pictures, look larger. So in the table above, the back edge looks wider than the front edge. In fact, the sides of the table are strictly parallel. The fact that they don’t get closer together with distance, as we expect them to following the rules of perspective, produces a specially strong size constancy effect.

Here’s another demo, the Wonky Window.

The right hand upper window is leaning the wrong way, which is wonky for a start, but it’s not quite as wonky as it looks. It’s really identical to the window of the left, and only seems to lean over more. That’s because the sides of the house, strongly converging with distance, produce an effect that we usually don’t notice. The greater the distance, at just the same time as the receding lines in perspective are converging, perceptual space is expanding, thanks to the size constancy effect. The width of the house at the level of the bottom of the windows expands with it, and so the parallel edges in each window appear to diverge. It’s a bit counter intuitive!

Another famous size-constancy effect (according to some) is the Moon Illusion.