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Depth Cues

There are many possible cues to depth, but that does not mean that the visual system uses them all (or that it weighs their respective influences evenly; or that they're all useful in all circumstances). Here, we list several depth cues, broken up into 3 categories: extraretinal (e.g., not from information on the retina), monocular (one eye), and binocular (2 eyes). This is just a partial list-- see if you can come up with others.

Extraretinal cues

Monocular cues

  • Linear perspective. Parallel lines facing the observer converge as they move away, toward the horizon.

  • Size gradient. The size of an image depends on the size of the object (of course) as well as it's distance from the viewer. This is especially obvious when viewing a regular, repetitive pattern; see such a texture gradient.

  • Height in visual field. Since our eyes are off the ground, objects at different distances project to different heights on the retina.

  • Shading and contours. Our visual system usually assumes lighting comes from above. The shape of a surface (convex or concave)- and hence the pattern of depth along its surface- is affected by shading.

  • Foreshortening. Related to size gradient, above.

  • Occlusion. Yes, objects that appear to "occlude" or block the view of other objects are perceived as closer in depth.

  • Atmospheric blur. When viewing a natural scene, the further things are, the more 'hazy' they look, due to moisture and other particles in the air.

  • Motion parallax. As you move your eyes side to side, closer objects move more in the visual field than further objects.

Binocular cues

  • Horizontal disparity (see text and notes).

Last modified: Thu Jul 15 01:21:22 PDT