Fig. 7. Evaluation of hypotheses for formation of on- and off-centre RGC mosaics. (A) Initial populations of 500 on-centre and 500 off-centre cells were created independently using the exclusion zone model (d_min=10 µm, =0.04; A=1 mm²). Up to 40% of cells were deleted (using the distance method) independently from each population. The mean and s.d. of the regularity index over ten simulations, with different initial conditions, are plotted for just the on- or off-centre cells (open or filled circles) and for the combined population of on- and off-centre cells (grey squares). Broken lines show the range of regularity indexes for the on- or off-centre RGCs, from Table 1. (B) Same as A, but d_min=15 µm (=0.09). (C) As in A, but an initial population of 1000 cells was created using the exclusion zone model (d_min=10 µm, =0.08) and then divided into on- and off-centre subpopulations by randomly assigning each cell to one of two types. (D) As in A, but an initial population of 1000 cells was created using the exclusion zone model (d_min=0 µm, =0) and divided into on- and off-centre subpopulations by nearest-neighbour inhibition (NNI). The d_min value in B was chosen so that the regularity of the on- and off-centre mosaics were similar to those in D before cell death.