def _doTopDownInfer(self, topDownInput = None):
return None, None<EOL>
Do one iteration of top-down inference.

Parameters:
--------------------------------------------
tdInput:      Top-down input

retval:     (spatialTopDownOut, temporalTopDownOut)
              spatialTopDownOut is the top down output computed only from the SP,
                using it's current bottom-up output.
              temporalTopDownOut is the top down output computed from the topDown in
               of the level above us.