LEFT AND RIGHT IN THE VISUAL 
PATHWAY
The right visual field extends 
out to the right almost to 90 
degrees, as you can easily verify 
by wiggling a finger and slowly 
moving it around to your right. 
It extends up 60 degrees or so, 
down perhaps 75 degrees and to 
the left, by definition, to a 
vertical line passing through 
the point you are looking at.

    The optic fibers distribute 
themselves to the two lateral 
geniculate bodies in a special 
and, at first glance, strange 
way. Fibers from the left half of 
the left retina go to the 
geniculate on the same side, 
whereas fibers from the left 
half of the right retina cross at 
the optic chiasm and go to the 
opposite geniculate, as shown 
in the previous figure; 
similarly, the output of the two 
right half-retinas ends up in 
the right hemisphere. Because 
the retinal images are reversed 
by the lenses, light coming 
from anywhere in the right half 
of the visual environment 
projects onto the two left half-
retinas, and the information is 
sent to the left hemisphere.

    The term visual fields refers 
to the outer world, or visual 
environment, as seen by the 
two eyes. The right visual field 
means all points to the right of 
a vertical line through any 
point we are looking at, as 
illustrated in the diagram to 
the left. It is important to 
distinguish between visual 
fields, or what we see in the 
external world, and receptive 
field, which means the outer 
world as seen by a single cell. 
To reword the previous 
paragraph: the information 
from the right visual field 
projects onto the left 
hemisphere.