Visual object formation from fragmentary information depends on two complementary processes: a contour interpolation process that interpolates between visible edge fragments and a surface interpolation process that connects similar regions across gaps. It has been suggested that each process can operate in the absence of the other, but this hypothesis has received little experimental study. Here we investigate spatiotemporal object formation (completion across gaps in both space and time) when contour- and surface-based processes are congruent or incongruent. We used the shape discrimination task of Palmer, Kellman & Shipley (JEP:General, 2006, Vol-135, 513-541) to investigate the degree of unit formation. In this paradigm, shape discrimination is enhanced when visible object fragments fulfill the geometric conditions for contour interpolation ("spatiotemporal relatability") relative to control ("non-relatable") displays. In the present study we investigated incongruent conditions: (1) non-relatable displays with coherent surface properties (same color, texture or shading pattern) and (2) relatable displays with bits with different surface properties (e.g. three different color), along with congruent displays. Results showed that shape discrimination performance was completely predicted by unit formation due to relatability of contours and not by surface properties. These results indicate the primacy of contour interpolation in determining object shape.

Palmer, E. M., Kellman, P. J., & Shipley, T. F. (2006). A theory of dynamic occluded and illusory object perception. Journal of Experimental Psychology: General, 135, 513–541.