Differential processing of reflection and rotation symmetries in visual textures
Rachel Moreau, Nihan Alp, Alasdair D. F. Clarke, Erez Freud, Peter Jes Kohler · Journal of Vision · 2021
Symmetries of various types are prevalent in the natural world. Psychophysical studies show that reflection symmetry (found in faces, bodies) can be detected preattentively, requiring less cognitive resources than other symmetry types such as rotation (found in flower petals, snowflakes). The distinction between symmetry types is important to our understanding of how symmetries contribute to perception of scenes and objects. Visual search has previously been used to probe the distinction between serial and parallel processing of cues to object shape (Enns and Rensink, 1991). Here we employ a visual search paradigm with symmetries that are embedded within regular textures. Our goal is to enhance our understanding of the mechanisms responsible for perceiving symmetries in textures, and differentiate between reflection and rotation symmetry. Based on previous findings, we hypothesize that reflection will elicit more parallel processing than rotation. We conducted two visual search experiments in which participants were presented with regular textures consisting of arrays of tiles containing symmetries. Participants were asked to report the presence of a target tile that had no symmetry and thus disrupted the regularity. We used four different array sizes (total # tiles: 9, 16, 25, 36), and trials with each array size were presented in an interleaved fashion. In Experiment 1, the non-target tiles contained reflection symmetry (N=133), while in Experiment 2 they contained rotation symmetry (N=148). In both experiments we found that accuracy was reduced and RT was increased as array sizes got larger, consistent with serial processing. Importantly, this array size effect was reduced for reflection symmetry relative to rotation symmetry. These results suggest that reflection symmetry elicits more parallel processing than rotation and that the two symmetry types can be differentiated in terms of the mechanisms required for perceiving them.