This leaves unsettled the 
part that type 1 cells play in 
color vision--if they play any 
part at all. These are the most 
common cells in the lateral 
geniculate body, and they 
supply the lion's share of the 
input to the visual cortex. Their 
obvious color coding makes it 
easy to lose sight of the fact 
that they are beautifully 
organized to respond to light-
dark contours, which they do 
with great precision. Indeed, in 
the fovea, where their centers 
are fed by one cone only, they 
have no choice but to be color-
coded. (The mystery is why the 
surround should be supplied by 
a single, different, cone type; it 
would seem more reasonable for 
the surrounds to be broad-
band.) Given this massively 
color-coded input it is 
astonishing that interblob cells 
in the cortex show so little 
interest in color. The few 
exceptions respond to red slits 
but not to white ones, and are 
thus clearly color coded. For 
the most part it would seem that 
the information on wavelength 
carried by type 1 cells is pooled, 
and the information about color 
lost. In one sense, however, it 
is not discarded completely. In 
Freiburg, in 1979, Jürgen 
Krüger and Peter Gouras showed 
that cortical cells often 
respond to lines formed by 
appropriately oriented red-
green (or orange-green) borders 
at all relative intensities of red 
and green. A truly color blind 
cell, like a color blind person, 
should be insensitive to the 
border at the ratio of 
intensities to which the cones 
respond equally. These cells 
presumably use the type 1 color 
information to allow contours 
of equal luminance to be visible 
by virtue of wavelength 
differences alone--of obvious 
value in defeating attempts at 
camouflage by predators or prey.

    The recognition of colors as 
such would thus seem to be an 
ability distinct from the ability 
to detect color borders, and to 
require a separate pathway 
consisting of type 2 cells and 
color-opponent blob cells. Our 
tendency to think of color and 
form as separate aspects of 
perception thus has its 
counterpart in the physical 
segregation of blobs and 
nonblob regions in the primary 
visual cortex. Beyond the 
striate cortex the segregation is 
perpetuated, in visual area 2 
and even beyond that. We do not 
know where, or if, they 
combine.