Fig. 9. How the precision of the collicular map projected on the retina changes over time for the four cases described in Figs 7, 8. The receptive field size (blue line) is the mean diameter of the receptive fields of the collicular cells; the receptive field separation (dashed line) is the mean distance between receptive field centres from neighbouring collicular cells. Both measures are expressed as ratios to the mean spacing between neighbouring retinal cells. Time plotted on a logarithmic scale. (A) The development of the normal map shown in Fig. 7A. Both size and separation decrease with time until they are comparable with the average spacing between retinal cells. (B) The development of the disordered map shown in Fig. 7B. The receptive field size stays at a high level; initially all receptive field centres congregate in one small region of the retina before they increase to give a large field separation. (C) The development of an ordered map with weak counter-gradients (Fig. 8A). Precision measures evolve as in A. (D) The development of a distorted map under the influence of strong counter-gradients (Fig. 8B). The final field size is significantly greater than in C, with the map being more disordered.