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Fig. 6.7. Reorganization of the orientation map after a retinal scotoma. In the top row, the RF centers of every third neuron in the network are plotted as a grid in the retinal space; the bottom row displays the corresponding map of orientation preferences (selectivity is not shown). The RF centers in the grids are calculated from the settled response (instead of the afferent weights as e.g. in Figure 5.11; Appendices G.2 and G.3), because the lesioned map is not in equilibrium with the input. The dotted white line shows the cortical scotoma, i.e., the region of V1 corresponding to the lesioned area of the retina. (a) Before the scotoma, the RF centers are organized into a retinotopic map with orientation-based distortions, as in Figure 5.11. (b) Shortly after the scotoma, neurons whose RFs were entirely covered by the scotoma retain their old RFs, but the surrounding neurons start to reorganize their afferent weights into the periphery of the scotoma. (c) Five thousand iterations after the scotoma, most of the receptive fields have moved out into the periphery of the lesion (with corresponding inward changes in perception as demonstrated in Figure 6.8); how many remain in the center depends on how large the scotoma is compared with the RFs and the lateral connections. The orientation map is unchanged within the central region of the scotoma, but along the cortical scotoma boundary (in white) many neurons have become selective for the orientation of the boundary, and the rest of the map has adapted to these changes. The reorganization of the retinotopic map provides a detailed computational account for the outward shift in the RF center found by Chino et al. (1992; Section 6.1.1), while the changes in the orientation map constitute predictions for future experiments. An animated demo of the reorganization process can be seen at ...