There’s a whole bunch of cues that people can use to judge distance. The following are the key ones.
<digs out old textbook to make sure I get everything>
Accommodation is refocusing of the eye.
Convergence is the angle of your eyes toward or away from your nose.
Size is regarded as being judgemental rather than perceptual. (You have to know how big the traget is in order for this to work.)
The ground plane affects perspective and texture gradients–something that you’re familiar with. Parallel lines converge in the distance; patterns get finer farther away (note that this is indepent of absolute size judgment).
Binocular disparity is your eyes getting two different pictures since they are separated in space.
Occlusion: Whether something is in front of another.
Height in visual field: Things that are farther away tend to be higher in the visual field.
Aerial perspective: Stuff gets blurry when it’s far away due to moisture and pollutants in the air.
Motion perspective: Move your head back and forth. Near objects seem to move a lot, distant objects not so much.
Different cues contribute to greater or lesser degrees at different distances. For example, convergence and accommodation are good out to about arm’s length; binocular disparity is good out to about 11 meters; but occlusion works at any distance.
Gillam, B. (1995). The Perception of Spatial Layout from Static Optical Information. In Epstein, W. and Rogers, S (eds). Perception of Space and Motion. San Diego: Academic Press.
Cutting, J. and Vishton, P. (1995). Perceiving Layout and Knowing Distances: The Integration, Relative Potency, and Contextual use of Different Information about Depth. In Epstein, W. and Rogers, S (eds). Perception of Space and Motion. San Diego: Academic Press.