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Fig. 4.9. Self-organized V1 lateral weights. The lateral excitatory (a) and inhibitory (b) weights for the sample neuron at the center of V1 are plotted on V1 as in Figure 4.3b,c; the small white square in (b) marks the neuron itself and the jagged black outline traces the original connectivity before self-organization and pruning. The combined profile (c) shows inhibitory weights subtracted from the excitatory, and illustrates the total effect of the lateral connections: Dark indicates a net inhibitory effect, white a net excitatory effect, and medium gray no net effect. During self-organization, smooth patterns of excitatory and inhibitory weights emerged, resulting in a DoG lateral interaction profile. Near the edge of the network this profile is elongated along the edge, as shown in Figure 4.7b. Such profiles sharpen the response of the network and allow an accurate retinotopic organization to develop.