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Fig. 6.6. Retinal activation and V1 response before and after a retinal scotoma. The initial and settled responses of the intact network (top row) and the lesioned network (bottom row) to input in (a) are shown in (b) and (c). The activations are displayed in gray scale from white to black (low to high; the orientation preferences of active V1 neurons are not shown). The retinal lesion is simulated by setting the activity of a set of receptors to zero, as shown in the bottom row of (a). The dotted line in (a) marks the lesioned area on the retina (the retinal scotoma), and in (b) and (c) marks the corresponding portion of V1 (the cortical scotoma). The cortical scotoma is approximately as wide as the lateral connections, matching artificial scotomas in biological experiments. Many of the neurons that responded to the intact input do not receive sufficient activation in the lesioned network and remain silent (because the topography of the retinal preferences is not uniform around the edges, some neurons inside the cortical scotoma still respond). Such changes in activity disrupt the dynamic equilibrium, forcing the network to reorganize.