Multistable grouping beyond the dot lattice: Individual and contextual differences in interactions of global orientation and local shape.

Previous research on perceptual grouping has focussed on discovering and understanding grouping principles and their interactions on both a group and an individual level. However, the studied set of grouping principles does not consider the complexity of interactions between the local and global level. In this study, dot lattices were adjusted to have various oriented shapes as elements. In addition to proximity between the elements, the use of triangles as elements provided a direct (i.e., alignment of the shape's side and the global orientation promoting good continuation) as well as an indirect grouping cue (i.e., perceived pointing in local triangles as a result of its global reference frame) promoting global groupings. We replicated the well-studied proximity effect. In addition, the introduction of shapes as elements resulted in a dampening of the proximity effect, regardless of the nature of the shape. The grouping effect of triangles, however, was dependent on the grid characteristics and differed between individuals. In a grid with small elements, most participants adhered to grouping by pointing. When the size of the elements was increased, there was a shift towards grouping by base-alignment. In both grid types, a relatively large group of participants did not exhibit consistent grouping by alignment nor pointing. These results confirm that oriented shapes can function as grouping cues in both a direct (i.e., alignment) and an indirect (i.e., pointing) manner. Moreover, they emphasize the importance of studying individual differences in perceptual grouping.