Can a competition between grouping principles be resolved without attention?

The goal of the present study was to examine whether attention is required for resolving the competition between two grouping principles operating on the same elements in the display. To this end, we used an inattention paradigm, in which the observer's attention was focused on a central task while irrelevant grouping displays were presented in the unattended background. The background displays were organized into two organizations, each of which was previously found to occur under inattention when presented alone: grouping into shapes (square/triangle) by element connectedness, and grouping into rows/columns by color similarity. On each trial, participants performed a demanding change-detection task on a small target matrix at fixation. Independently of any change in the target, the unattended grouping organizations in the background could change or stay the same, independently in each of the grouping organizations, creating congruency relations between the central target and the background organizations. Congruency effects were expected if the background organizations could be achieved under inattention. However, if the competition between grouping principles cannot be resolved without attention, congruency effects are not expected to emerge. We found that changes in the background organization by connectedness produced congruency effects upon the accuracy of the target-change judgments: target 'same' responses were more accurate when the background shape stayed the same than when it changed, and target 'different' responses were more accurate when the shape changed than when it stayed the same. However, no congruency effect was found for the organization by color similarity. When probed with surprise questions, participants could not report the organization on which the target appeared in the preceding display or whether the organization had changed on the preceding trial, confirming the condition of inattention. These results suggest that the competition between grouping principles can be resolved without attention.