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How does binocular parallax help people judge the distance of nearby objects?

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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.

Binocular parallax, also known as binocular disparity, is a primary cue for depth perception that allows humans to judge the distance of nearby objects. Because the eyes are positioned at different points in the skull, each eye receives a slightly different image of the same object.12

The brain interprets this difference as a three-dimensional experience. Specifically, the degree of disparity depends on the difference between the angles at which an object is fixed by the left and right eyes. The binocular parallax of any point in space is defined by the angle subtended at that point by the line joining the nodal points of the two eyes.21

When viewing objects, the brain fuses these disparate images into a single perception of depth. The greater the parallax difference between the two retinal images, the closer the object is perceived to be. This phenomenon is most effective in near space, as the angular difference between retinal images diminishes significantly when viewing distant objects.12