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How does motion parallax help a person judge distance using one eye?

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Diagram illustrating how astronomers calculate the distance to a star using parallax: Earth is shown in two positions on opposite sides of its orbit around the Sun, with lines extending to a nearby star X and further to distant background stars. The apparent shift in star X's position, measured as angle A, is used to determine its distance, with the baseline labeled as 186,000,000 miles. — Parallax Calculating stellar distances.

Motion parallax, also referred to as visual movement parallax, is a crucial monocular cue that allows a person to judge distance and depth when using only one eye.1

This phenomenon occurs when an observer moves their head, either from side to side or forward and backward. As the observer moves, the images of objects in the visual field shift across the retina at different rates depending on their distance from the observer. Specifically, objects that are closer to the observer appear to move more across the visual field, while objects that are further away appear to move less.12

By observing these relative changes in the position of objects, the brain can interpret the spatial relationships and estimate the distance of those objects. Unlike binocular disparity, which requires two eyes to perceive depth through the difference between two retinal images, motion parallax provides an effective way to perceive three-dimensional space using only one eye.12