As a relation of objects in the 
world, interposition is simple 
enough to grasp, but, as a 
perceptual phenomenon, it is 
difficult to explain. The central 
problem can be seen by trying 
the following experiment. Cut 
out two cardboard objects, a 
circle and a rectangle. Cut a 
small notch in the circle into 
which the corner of the 
rectangle can fit, as shown in 
the illustration at left. Then 
align the two objects as shown, 
with the rectangle behind the 
circle. When you view the 
objects with one eye from the 
appropriate vantage point, it 
will seem that the rectangle is 
occluding the circle and you 
will receive the impression 
that the rectangle is nearer. 
But note that the stimulus your 
eye receives is ambiguous. You 
could just as easily perceive the 
arrangement veridically (as it 
is) as perceive it as two objects 
in the same plane fitted 
together like a jigsaw puzzle. 
The conclusion that the 
interposition depth 
interpretation is preferred 
therefore seems warranted.