back to 'Seeing in 3D'
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.
- Vergence ("convergence") of the eyes varies (crosses or uncrosses) as you fixate on near and far objects.
- Accomodation. The amount of accomodation that the eye (lens) performs to focus on an object varies with depth.
- 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.
- Horizontal disparity (see text and notes).
Last modified: Thu Jul 15 01:21:22 PDT