RETINAL DISPARITY 
A hand-held stereoscope: half-
lenses allow the directions of
gaze of the two eyes to remain
parallel so that each eye can 
view a different figure. The 
stereoscope recreates the 
effect of viewing a single scene 
at a great distance.

By closing one eye, we have 
eliminated whatever 
information might be provided 
by the simultaneous utilization 
of the two eyes together. 
Investigators distinguish two 
separate factors here, retinal 
disparity and convergence. 
When we view objects with both 
eyes open, the images of the 
objects projected on each retina 
are slightly different, or 
disparate, because the eyes are 
in slightly differing positions 
with respect to the scene, 
roughly 2.5 inches apart on the 
average.