Nonmetrical: info about one object in front of another, nothing about how large it is. Metrical depth: some distance info relative depth: something is farther, (a lot, a little) Assume depth: don"t get depth information from visual signal, its a good guess usually. How do we figure out that 3rd information - cuz depth is not given in visual info. Visual system takes a lot of info from world that isn"t variable and combines it to guess what the distance is. Monocular and binocular: one eye or require 2 eyes. Accommodation (monocular): focus on close things: round thick lens. Problem: only works within the areas that there is variability of lens thickness - there is a limited range: between near and far point. Vergence movements: your eyes move to focus on object. Brain uses info from muscles to see how much convergence there is. Limitation: only gives info to about 2 meters, eyes can"t diverge anymore.