Hans Wallach and his 
associates at Swarthmore 
College showed just such a 
learning process at work in 
depth perception, although not 
with respect to linear 
perspective. In one 
experiment, they used a simple 
wire object, selected for having 
a projection that would not 
convey any impression of 
three-dimensionality at the 
outset. Subjects were first 
shown a shadow pattern of such 
a wire object cast on a screen, 
which they perceived as two-
dimensional. Then the 
investigators set the wire object 
in motion, creating a kinetic 
depth effect in which the 
transforming shadow pattern 
yielded a three-dimensional 
impression. Finally, the 
subjects viewed the shadow 
pattern when it was again 
stationary. They now perceived 
it to be three-dimensional. 
Presumably, therefore, 
observers learned that this 
two-dimensional pattern 
signified a three-dimensional 
object and they perceived it 
accordingly.