How do flankers' relations affect crowding?

The visual system can integrate discrete units of information to construct a coherent description of the input it receives. Little is known about the processes of grouping and their implementation in the visual system. Previously we described a configural effect in which the global arrangement (degree of co-circularity) of Gabor flankers affected the degree of crowding with a Gabor target that they surrounded. Here we tested possible mechanisms by which the configural effect might operate in crowding. We ruled out simple explanations based on the effect of basic units constructing these configurations (pairs of opposing Gabors). Our results support an explanation for crowding that is based on grouping processes between flankers. They also suggest that not all flankers necessarily directly affect the target. Flankers might group together and interact with the target as a single element. Finally, using a computational model of crowding based on compulsory grouping (following Gestalt principles) and segmentation, we define the relative contribution of different pair relations of grouped elements to crowding.