Neurons in the visual cortex respond best to rod-like stimuli of given
orientation. While the preferred orientation varies continuously across most of
the cortex, there are prominent pinwheel centers around which all orientations
a re present. Oriented segments abound in natural images, and tend to be
collinear}; neurons are also more likely to be connected if their preferred
orientations are aligned to their topographic separation. These are indications
of a reduced symmetry requiring joint rotations of both orientation preference
and the underl ying topography. We verify that this requirement extends to
cortical maps of mo nkey and cat by direct statistical analysis. Furthermore,
analytical arguments and numerical studies indicate that pinwheels are
generically stable in evolving field models which couple orientation and
topography