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Fig. 13.12. Contour completion process. (a) The four contour elements in the input with a gap in the middle correspond to one side in the edge-detected Kanizsa triangle (the dashed oval in Figure 13.4). In the MUA plot, the four contour elements are shown in the bottom and the top (rows 1-2 and 4-5) and the gap in the middle (row 3). Even though there were no inputs in the middle, the cortical area representing the gap is activated, and the activations are synchronized with the other four MUA sequences. This behavior indicates that contour completion occurred and the gap is perceived as an illusory edge. (b) In the second experiment, the input consisted of two contour elements from only one side of the gap. The MUA sequence for the gap is silent (row 3), indicating that contour completion did not occur. Thus, both sides of the gap need to be stimulated for the gap to be perceived as an edge.