How does binocular disparity help the brain judge depth and distance?

Binocular disparity is a primary cue for depth and distance perception that relies on the fact that our eyes are positioned at different points in the skull, causing them to receive slightly different images of the same object.1

The brain judges depth through the following biological processes:

• Retinal Disparity: Because the eyes view objects from slightly different angles, the images formed on the two retinas are not identical. The brain processes these dissimilar images to create a three-dimensional experience.12
• Fusion of Disparate Images: The brain possesses the ability to fuse these slightly different, or "disparate," images into a single, coherent perception. When the disparity between the two images is within a specific range—known as Panum’s fusional area—the brain interprets the difference as depth rather than seeing double.2
• Cortical Processing: Specialized nerve cells in the visual cortex act as "disparity detectors." These cells assess the small displacements between the two retinal images to calculate binocular parallax, allowing the brain to perceive objects at varying distances from the fixation point.23

This mechanism is most effective in near space, as the angular difference between retinal images diminishes as objects move further away.1