Fig. 6.

Enhancement of the Cornsweet illusion by the addition of perspective. A, The stimulus is the same as in Figure 2B, but foreshortened to indicate that the two flanking regions extend away from the observer. As indicated in Table 1, perspective enhances the difference in brightness between the two flanking territories. (Note that adding perspective requires an increase in the width of the flanking regions to maintain the ratio of the edge gradients to total surface area). B, Diagram of the stimulus source made more likely by this presentation. As in other manipulations, the addition of perspective only alters the probabilities related to the stimulus source, because the two territories in this presentation could still lie in the same plane if they happened to have the particular shapes that can also indicate a diminution of size with distance.