3

THE MANY PATHS TO THE THIRD 
DIMENSION

    The seemingly infinite 
distance and expanse over the 
cacti and through the desert to 
the mountains beyond is 
immediately apparent in the 
photograph to the left. What is 
it in the photograph that yields 
such a striking sense of 
distance? If we viewed the 
scene ourselves rather than 
merely the picture of it, what 
other factors would enter the 
equation to add to the powerful 
impression of depth?

    We take the three-
dimensional world in which we 
find ourselves so much for 
granted that we seldom think of 
our ability to perceive how far 
away things are from us and 
from each other as an 
achievement calling for 
explanation. If we possessed a 
three-dimensional retina and a 
mechanism that registered the 
distance of a thing by its 
location in such a retina, our 
ability to perceive depth might 
be less remarkable. But the 
human retina is effectively a 
two-dimensional surface. Thus 
the puzzle of depth perception 
is how we gain information 
about distance, and how we 
make use of this information to 
reconstruct a three-
dimensional perceptual world.