Chapter 4. Combined first and second difference edge sensing.
For many years, as discussed in Chapter 2, it has been postulated at B.Ae. that biological vision
systems, by and large, are organised to sense 1st differences of scene luminance in space and time.
Such a hypothesis has proved to be very robust in multi-dimensional parameter space for human
visual threshold modelling. On the other hand, as discussed in Chapter 3, it has to be admitted that
the early processes of vision appear to behave like Laplacian operators, thereby providing, it would
seem, second differences of scene luminance. When we first attempted to set up a simulation of