i've had this problem for a while (i now realize): i have trouble telling how close (or far) something is to me when the object isn't in visual field. specifically, if i'm looking at something it isn't a problem but if someone is walking behind me i can't tell if they are a foot or 10 feet away, for example. similarly, if i'm walking under a low overpass or ceiling i can't tell if it's an inch or 10 inches.

what could this relate to? any thoughts on fixing this?