Fixes LGN RF fields to be balanced by scaling center and surround regions.
This is necessary at the edges of the visual field area where the DOG RF is
cut into by the boundary. This was intended to be a fix so that natural
images would work to train the binocular RF, and it works now. The problem
was with unbalanced RFs was that they were strongly activated by the natural
images (which tend to be dark on average and/or have large regions that are
lighter or darker than mean gray) so activity of the BN was driven by these
LGN cells and the RF evolved to depend highly on them.