In the experiment, 
subjects did perceive a slanted 
plane (although the slant they 
perceived was not as great as 
the actual slant), and they 
perceived the depth much more 
accurately when the sheet 
moved than when it was 
stationary. Notice that in this 
experiment it is the display 
that moves, not the observer. It 
was presumed, though, that the 
exact same kind of information 
would be available were the 
display to be stationary and the 
observer to move, as is more 
typically the case in daily life. 
 
    Motion can create the 
impression of depth in other 
ways as well. For example, the 
shadow cast on a screen by a 
thin, tilted rod attached to a 
wire stem will appear to 
observers to be in a frontal 
plane, but, if the object is 
rotated, observers will perceive 
the pattern of cast shadows as 
an object rotating in the third 
dimension. That is, when the 
object is rotated, observers 
perceive veridically that it is a 
rigid thing tilted in the third 
dimension, not a thing 
changing in length and tilt in a 
frontal plane. Hans Wallach 
and his associates, who first 
conducted experiments along 
these lines, termed this 
phenomenon the kinetic depth 
effect. Again, we would expect 
the same outcome were the 
observer to circle the wire 
object from a distance of 
several feet, viewing its 
changing projection with one 
eye closed. Were the observer to 
remain stationary, the object 
would probably appear to be in a 
frontal plane because all other 
cues would be eliminated.