Here is a copy of the model where the input is a ramp.  You can manipulate the size of the center and surround fields just as on the other page.  You  can also alter the input any way you like.  It is awkward and I hope to make it easier eventually but I make no promises.  Still, I hope you find these pages with this crude, simplistic, but awkward, and inelegent model of some use.

This next page looks at one way to include eye tremor in the model.

This directory contains some of the variations I have played around with.  There are brief descriptions of the phenomena and some of the questions that they raise.