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Fig. 8. The effects of introducing fixed counter-gradients of EphA over the
rostrocaudal axis of the colliculus. (A) The simulation of Fig. 7A
was repeated with a weaker initial concentration gradient over the
rostrocaudal axis of 0.4x + 0.25II together with a weak counter-gradient of
EphA. The contribution from the counter-gradient is assumed to have the same
functional form as the EphA gradients in the retina. At a distance x this is
0.005 + 0.013e-2.3x + 0.005II. (B) As A but with a
four times stronger counter-gradient resulting in a distorted map.