Grouping by proximity or similarity? Competition between the Gestalt principles in vision

The nature of the psychological processes that underlie the Gestalt principles of grouping by proximity and grouping by similarity is examined. Similarity was defined relative to the principles of grouping by common colour and grouping by common shape. Subjects were presented with displays comprising a row of seven coloured shapes and were asked to rate the degree to which the central target shape grouped with either the right or the left flanking shapes. Across the displays the proximal and featural relationships between the target and flankers were varied. These ratings reflected persuasive effects of grouping by proximity and common colour; there was only weak evidence for grouping by common shape. Nevertheless, both common colour and common shape were shown to override grouping by proximity, under certain conditions. The data also show that to understand how the Gestalt principles operate it appears necessary to consider processes that operate within and between groups of elements that are initially identified on the basis of proximity. Whether such groups survive further analysis depends critically on the featural content of the constituent elements.