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Fig. 10.4. Self-organization of the scaled-up orientation map. These figures show a scaled-up version of the "Disks" simulation from Figure 9.1, eight times wider and eight times taller. At this scale, each input includes multiple disks (a), the afferent weights of each neuron span only a small portion of the retina (drawn to scale in e) and the lateral weights only a small part of V1 (drawn to scale in f ), and the orientation map has many more orientation patches (g). Its Fourier transform (i) is still ring-shaped and its OR histogram (h) flat. Zooming in on the central 36 × 36 portion of this 288 × 288 map, plot (j) also shows that the local structure and selectivity of the map are similar to those in Section 9.2. The map appears blockier because the neuron density was reduced to the smallest acceptable value so that the network would be practical to simulate. Plot (c) shows that the orientation preference of each neuron that responds to the input (plotted as in Figure 6.5) is still a good match to the orientation of the input at that retinal location, and the histogram of the responses is unbiased, although noisy (d). Thus, this network is a reasonable approximation to a large area of V1 and the retina.