There is no question that the visual system does perform a figure-ground segregation; I merely suggest that the problem of contrast v.s. assimilation is related to the figure / ground issue, and that the outcome of the figure / ground computation influences the brightness perception mechanism. The new draft now includes the text: "This does not of course shed any light on how the figure / ground segregation occurs, but merely suggests that the problem of contrast v.s. assimilation is related to the percepton of figure v.s. ground, as suggested by Taya et al. (1995). The contribution of the Gestalt approach is that since the effects of brightness contrast and assimilation are observed to spread spatially over large regions of the image, therefore isomorphism suggests that a spatial diffusion or field-like influence is involved in generating those percepts, and Grossberg offers a dynamic model to explain this diffusion mechanism."