The effect of overall stimulus configuration on crowding

The standard framework to study vision is typically hierarchical and feedforward, which facilitates deconstructing complex mechanisms into smaller, more tractable problems. However, this framework can fail when elements are presented in context, as they are in every-day life. In crowding, peripheral discrimination is hindered by nearby elements, as for example a Vernier embedded in a square is more difficult to discriminate than when presented alone. However, adding additional flanking squares can, counterintuitively, ameliorate this deleterious effect (Manassi et al, 2013, J Vis). Clearly, in order to understand low-level vision, we must also understand higher-level processing. Here, we take a step toward goal by characterizing the effect of flanker configuration on crowding in a theory-agnostic manner. Previous studies have examined a small number of experimenter-selected configurations; here, we made no assumptions about which configurations should affect crowding. We placed a Vernier embedded in a square at the centre of all possible 3x5 arrays with an equal number of squares and stars (3432 total). Observers discriminated this Vernier in the presence of each configuration, repeating each until responding incorrectly or achieving six correct responses. In this way, we were able to quantify the effect of all possible configurations on performance. Among the interesting patterns in our data set, we observed a strong positive correlation between the number of clustered square elements and performance. More generally, our data suggest that configurations encouraging separate grouping of target and flankerelements ameliorate crowding, using a paradigm in whichgrouping was not explicitly manipulated.