| topLeft | repeats the image in Figure 1.3 |
| topRight | shows again the long-range cooperation and short-range compeition that are controlled by the bipole grouping process (Figure 4.43a middle panel) |
| bottomLeft | shows the end gaps that are caused by these bipole grouping mechanisms |
| bottomRight | shows how surface filling-in is contained within the closed horizontal rectangular boundary, but spills out of the end gaps formed in the other two rectangles |
