Illusion - Is Seeing Really Believing?/Illusion - Is Seeing Really Believing (1998)(Marshall Media)[Mac-PC].iso/pc/illusion/hub_fie.cxt/00209_Field_frep130.txt

Text File | 1996-12-30 | 2KB | 52 lines

    The next step was to look at
the receptive fields of these
cells by using small spots of
colored light, as Torsten Wiesel
and I did in 1966, instead of
diffuse light. For most of De
Valois' opponent-color cells,
the receptive fields had a
surprising organization, one
that still puzzles us. The cells,
like Kuffler's in the cat, had
fields divided into antagonistic
centers and surrounds; the
center could be "on" or "off".
In a typical example, the field
center is fed exclusively by red
cones and the inhibitory
surround exclusively by green
cones. Consequently, with red
light both a small spot and a
large spot give brisk responses,
because the center is
selectively sensitive to long-
wavelength light and the
surround virtually insensitive;
with short-wavelength light,
small spots give little or no
response and large spots
produce strong inhibition with
off responses. With white light,
containing short and long
wavelengths, small spots evoke
on responses and large spots
produce no response.

In a typical type 1 receptive
field, the center receives
excitatory input from red
cones; the surround, inhibitory
input from green cones.

    Although our first
impression was that such a cell
must be getting input from red
cones in the center region and
green cones in the surround, it
now seems probable that the
total receptive field is a
combination of two overlapping
processes, as illustrated in the
figure to the left.