THE IMPLICATIONS OF SINGLE-
CELL PHYSIOLOGY FOR 
PERCEPTION
How are cells in our brain 
likely to respond to some 
everyday stimulus, such as this 
kidney-shaped uniform blob? In 
the visual cortex, only a select 
set of cells will show any 
interest.

    The fact that a cell in the 
brain responds to visual stimuli 
does not guarantee that it plays 
a direct part in perception. For 
example, many structures in 
the brainstem that are 
primarily visual have to do only 
with eye movements, pupillary 
constriction, or focusing by 
means of the lens. We can 
nevertheless be reasonably 
sure that the cells I described 
in this chapter have a lot to do 
with perception. As I mentioned 
at the outset, destroying any 
small piece of our striate cortex 
produces blindness in some 
small part of our visual world, 
and damaging the striate cortex 
has the same result in the 
monkey. In the cat things are 
not so simple: a cat with its 
striate cortex removed can see, 
though less well. Other parts of 
the brain, such as the superior 
colliculus, may play a 
relatively more important part 
in a cat's perception than they 
do in the primate's. Lower 
vertebrates, such as frogs and 
turtles, have nothing quite like 
our cortex, yet no one would 
contend that they are blind.

    We can now say with some 
confidence what any one of 
these cortical cells is likely to 
be doing in response to a 
natural scene. The majority of 
cortical cells respond badly to 
diffuse light but well to 
appropriately oriented lines. 
Thus for the kidney shape 
shown in the illustration to the 
left, such a cell will fire if and 
only if its receptive field is cut 
in the right orientation by the 
borders. Cells whose receptive 
fields are inside the borders 
will be unaffected; they will 
continue to fire at their 
spontaneous rate, oblivious to 
the presence or absence of the 
form.