= because 2 eyes are offset, they produce 2 diff images on retina, so brain uses disparity to calculate depth
far object = not much disparity
close object = lots of disparity
ex. if bring finger closer to face and close each eye, finger shifts around more the closer it is to eyes
= looking at closer objects causes our eyes to converge
brain uses this info to calculate depth
when eyes view near object, muscles move eyes toward each other (strain)