Figure 1.

Spatial transformations. Left figures: Parallel lines and planes in physical space run from a screen (light blue) in front of an eye to infinity (just a finite part is shown). Center figures: Projections of the lines and planes on the frontal screen represent the proximal stimulus. Right figures: Visual space is postulated to be the 3-D expansion of the proximal stimulus in depth limited to a finite vanishing point. The vanishing point is in the straight-ahead direction in the top figures and in a rightward direction in the bottom figures. The light-red vertical plane indicates the sagittal plane.