Oculomotor Cues
Accommodation of the lens 
gives us cues to distance 
through the varying blurriness 
of objects.  But as represented 
in this photograph, 
accomodation loses its effect 
beyond a few feet: objects at 
differing distances will all be 
in relatively sharp focus.

In principle, it should be easy 
to determine if accommodation 
alone is a cue to the perception 
of depth. If you close one eye 
and view a solitary, unfamiliar, 
luminous object in a dark room 
with your head held still, the 
shape of the lens will 
automatically adjust itself for 
maximum sharpness of the 
image, based on the object’s 
distance. Such a method would 
test the use of lens 
accommodation as a cue to 
absolute distance; the 
information about distance 
would have to derive ultimately 
from the altered state of the 
ciliary muscles in the eye that 
governs the shape of the lens. 
To test the value of lens 
accommodation in gauging 
relative distance or depth, we 
need only add several more 
objects, at varying distances, in 
the same dark room. As the eye 
accommodates for one object’s 
distance, the images of the 
other objects will be blurred; 
the blurriness would 
presumably serve as a cue that 
those objects are not in the 
same plane as the one fixated. 
In this case, the information 
would come from the 
differential sharpness or blur 
of several simultaneously 
registered retinal images.