A long, narrow slit of light 
evokes a response wherever it 
is placed within the receptive 
field (rectangle) of a complex 
cell, provided the orientation is 
correct (upper three records). A 
nonoptimal orientation gives a 
weaker response or none at all 
(lower record).

    The diagram to the left for 
the complex cell and the 
response diagram shown 
previously for the simple cell 
illustrate the essential 
difference between the two 
types: for a simple cell, the 
extremely narrow range of 
positions over which an 
optimally oriented line evokes 
a response; for a complex cell, 
the responses to a properly 
oriented line wherever it is 
placed in the receptive field. 
This behavior is related to the 
explicit on and off regions of a 
simple cell and to the lack of 
such regions in a complex cell. 
The complex cell generalizes 
the responsiveness to a line 
over a wider territory.

    Complex cells tend to have 
larger receptive fields than 
simple cells, but not very much 
larger. A typical complex 
receptive field in the fovea of 
the macaque monkey would be 
about one-half degree by one-
half degree. The optimum 
stimulus width is about the 
same for simple cells and 
complex cells--in the fovea, 
about 2 minutes of arc. The 
complex cell's resolving power, 
or acuity, is thus the same as 
the simple cell's.