Illusion - Is Seeing Really Believing?/Illusion - Is Seeing Really Believing (1998)(Marshall Media)[Mac-PC].iso/pc/illusion/hub_fie.cxt/00075_Field_frep25.txt

Text File | 1996-12-30 | 2KB | 55 lines

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.