How does movement parallax help a person judge the distance of objects?

Movement parallax is a vital monocular cue that allows a person to judge the distance of objects by observing changes in their retinal images as the observer moves.1

When an individual moves their head—either from side to side or forward and backward—objects at different distances appear to shift at different rates across the field of vision. Specifically, the retinal image of a nearby object moves significantly more than the image of a more distant object. Furthermore, objects closer to the observer appear to move in the opposite direction to the movement of the head in relation to more distant points.12

Unlike binocular disparity, which relies on the slightly different images received by two eyes, movement parallax is especially important for depth perception when using only one eye (monocular vision). By interpreting the relative speed and direction of these image shifts, the brain can effectively estimate the relative positions of objects in space.12