The optimal stimulus for an 
end-stopped cell is a line that 
extends for a certain distance 
and no further. For a cell that 
responds to edges and is end 
stopped at one end only, a 
corner is ideal; for a cell that 
responds to slits or black bars 
and is stopped at both ends, the 
optimum stimulus is a short 
white or black line or a line 
that curves so that it is 
appropriate in the activating 
region and inappropriate--
different by 20 to 30 degrees or 
more--in the flanking regions, 
as shown in the diagram of the 
curved contour to the left. We 
can thus view end-stopped cells 
as sensitive to corners, to 
curvature, or to sudden breaks 
in lines.