ACCOMMODATION 

One potential source of 
information is not eliminated 
in our dark-room experiment. 
The lens of the eye reflexively 
changes its thickness in order 
to achieve sharp focus for 
objects at differing distances. 
Logically, if the brain "knew" 
about the state of 
accommodation of the lens, it 
could use such information as a 
clue to the object's distance. It 
could also gain information 
from the fact that objects 
farther or nearer than the 
object focused on will yield 
blurred images, the more so the 
farther away they are from the 
plane upon which the eyes are 
focused. Accommodation and 
convergence are often termed 
oculomotor cues because they 
depend on movements of (or 
within) the eye.

    Accommodation, as we 
shall see, is considered to be a 
weak source of information 
about depth. Therefore, it was 
not deemed necessary to 
eliminate it in our experiment. 
We could have eliminated this 
cue as well by simply viewing 
the object through a pinhole, or 
artificial pupil. The reason why 
a pinhole eliminates 
accommodation as a distance 
clue is easy to grasp. The 
pinhole allows only a single ray 
of light (or a very narrow beam) 
to reach the eye from any point 
in space. Thus a lens is not 
needed to focus the light. A 
sharp picture of a scene would 
be produced regardless of the 
distance of the objects in it.