Around 1950, Stephen 
Kuffler became the first to 
record the responses of retinal 
ganglion cells to spots of light 
in a mammal, the cat. He was 
then working at the Wilmer 
Institute of Ophthalmology at 
the Johns Hopkins Hospital. In 
retrospect, his choice of 
animals was lucky because the 
cat's retina seems to have 
neither the complexity of 
movement responses we find in 
the frog or rabbit retina nor the 
color complications we find in 
the retinas of fish, birds, or 
monkeys. Kuffler used an 
optical stimulator designed by 
Samuel Talbot. This optical 
device, a modified eye doctor's 
ophthalmoscope, made it 
possible to flood the retina with 
steady, weak, uniform 
background light and also to 
project small, more intense 
stimulus spots, while directly 
observing both the stimulus and 
the electrode tip. The 
background light made it 
possible to stimulate either rods 
or cones or both, because only 
the cones work when the 
prevailing illumination is very 
bright, and only the rods work 
in very dim light. Kuffler 
recorded extracellularly from 
electrodes inserted through the 
sclera (white of the eye) 
directly into the retina from 
the front. He had little 
difficulty finding retinal 
ganglion cells, which are just 
under the surface and are fairly 
large.

    With a steady, diffuse 
background light, or even in 
utter darkness, most retinal 
ganglion cells kept up a steady, 
somewhat irregular firing of 
impulses, at rates of from 1 to 2 
up to about 20 impulses per 
second. Because one might have 
expected the cells to be silent 
in complete darkness, this 
firing itself came as a surprise.

    By searching with a small 
spot of light, Kuffler was able to 
find a region in the retina 
through which he could 
influence--increase or 
suppress--the retinal ganglion 
cell's firing. This region was 
the ganglion cell's receptive 
field. As you might expect, the 
receptive field was generally 
centered at or very near the tip 
of the electrode. It soon became 
clear that ganglion cells were 
of two types, and for reasons 
that I will soon explain, he 
called them on-center cells and 
off-center cells. An on-center 
cell discharged at a markedly 
increased rate when a small 
spot was turned on anywhere 
within a well-defined area in 
or near the center of the 
receptive field. If you listen to 
the discharges of such a cell 
over a loudspeaker, you will 
first hear spontaneous firing, 
perhaps an occasional click, 
and then, when the light goes 
on, you will hear a barrage of 
impulses that sounds like a 
machine gun firing. We call 
this form of response an on 
response. When Kuffler moved 
the spot of light a small 
distance away from the center 
of the receptive field, he 
discovered that the light 
suppressed the spontaneous 
firing of the cell, and that 
when he turned off the light 
the cell gave a brisk burst of 
impulses, lasting about 1 
second. We call this entire 
sequence--suppression during 
light and discharge following 
light--an off response. 
Exploration of the receptive 
field soon showed that it was 
cleanly subdivided into a 
circular on region surrounded 
by a much larger ring-shaped 
off region.