Editing Depth perception (section)

=== {{visible anchor|Depth from motion}} ===

When an object moves toward the observer, the retinal projection of an object expands over a period of time, which leads to the perception of movement in a line toward the observer. Another name for this phenomenon is ''depth from optical expansion''.<ref>{{cite journal|last=Swanston|first=M.C.|author2=Gogel, W.C.|title=Perceived size and motion in depth from optical expansion|journal=Perception & Psychophysics|year=1986|volume=39|issue=5|pages=309–326|doi=10.3758/BF03202998|pmid=3737362|doi-access=free}}</ref> The dynamic stimulus change enables the observer not only to see the object as moving, but to perceive the distance of the moving object. Thus, in this context, the changing size serves as a distance cue.<ref>{{cite journal|last=Ittelson|first=W.H.|title=Size as a cue to distance: Radial motion|journal=American Journal of Psychology|date=Apr 1951|volume=64|issue=2|pages=188–202|doi=10.2307/1418666|jstor=1418666|pmid=14829626}}</ref> A related phenomenon is the visual system's capacity to calculate time-to-contact (TTC) of an approaching object from the rate of optical expansion{{snd}}a useful ability in contexts ranging from driving a car to playing a [[ball game]]. However, the calculation of TTC is, strictly speaking, a perception of velocity rather than depth.