Depth and Distance Perception

Perceptual processes function in the three‐dimensional organization of stimuli as well as in distance judgments. The processes include use of both monocular and binocular cues.

Monocular cues. Monocular cues, those used when looking at objects with one eye closed, help an individual to form a three‐dimensional concept of the stimulus object. Such cues include

  • size of the stimulus

  • interposition, when one stimulus blocks the image of another

  • shadows, which indicate distance

  • linear perspective, the convergence of parallel tracks or lines as they recede into the distance

  • texture changes (distinct bricks are seen in a near wall but become a pattern with increased distance)

  • relative motion (motion parallax), used in judging distance (when you are traveling in a car, near objects seen out the window seem to move rapidly, but far ones don't seem to move)

Binocular cues. Binocular cues, those used when looking at objects with both eyes, also function in depth perception. Examples are

  • retinal disparity, the differences in images on the retinas of the two eyes

  • eye convergence, a necessary visual response in order to focus on a distant object

Illusions. Presentation of multiple stimuli elicits a tendency to group some of them together and others apart, a phenomenon which can create optical illusions. An example is the Müller‐Lyer illusion shown in Figure . The lengths of the two lines appear to be different but are the same.

figure 1

The Müller‐Lyer Illusion