If the belief that a pictorial 
cue is an innate stimulus sign 
of depth is one theory and that 
it is a learned sign of depth is 
another, there is a third 
alternative, initially suggested 
by the Gestalt psychologists. In 
this view, the preference for 
the depth “solution” over the 
two-dimensional “solution” of 
what a pictorial stimulus 
pattern represents in the world 
is based on a tendency of the 
mind to prefer simplicity.

    Suppose, for example, that we 
are looking at the pattern 
shown to the far left, referred 
to as the Necker cube. We 
perceive it as three-
dimensional. Why do we not 
perceive it as a two-
dimensional arrangement of 
lines instead? The Gestalt 
answer is that the two-
dimensional percept is a much 
more complex structure than 
the three-dimensional percept. 
A regular cube is quite simple: 
all the faces are equal, as are 
all the angles, opposite sides 
are parallel, and so forth. Now 
consider the pattern shown to 
the right of the Necker cube. It 
tends to appear spontaneously 
as two-dimensional. Yet, if 
examined carefully, it can be 
seen to represent a regular cube 
tipped up on an edge, with the 
topmost point in the figure 
representing the top rear 
corner of the cube. For such a 
pattern, the two-dimensional 
percept is as “simple” as that of 
a cube: a hexagon with 
symmetrically placed straight 
lines inside it. Thus, the 
advantage of seeing it as a 
three-dimensional percept has 
disappeared.