We address the 3-D curvature contrast effect, the phenomenon whereby a curved object looks less curved when it is surrounded by one or more heavily curved surrounding objects. Previously (Kappers & Te Pas, ECVP 2000) we demonstrated that the 3-D curvature contrast effect could not only be induced by paraboloids containing second-order structure (curvature), but also by cones (first-order) with the same average slant as the paraboloids. A very much reduced contrast effect occurred when we used depth planes (zeroth-order) situated at the same average depth as the second order paraboloids. Although not significant, the contrast effect also seemed slightly reduced with first-order inducers than with second-order inducers. The aim of the present experiment is to test whether the contrast effect for first- and zeroth-order stimuli can be enhanced by using the maximum depth and slant that is present in the second-order paraboloids to define the first- and zeroth-order surrounds. As before, we find a strong contrast effect with both first- and second-order surrounds, but a very much reduced contrast effect with zeroth-order surrounds. When we use the maximum slant we find no reduction of the contrast effect for the first-order inducers. The present results suggest that the maximum slant present in the stimulus is enough to evoke the reported contrast effect. The results make it highly unlikely that direct access to curvature information is used in this task.