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Peter J. Kohler, Alasdair D. F. Clarke, Joan Liu-Shuang, Yanxi Liu, Anthony M. Norcia; The neural response to visual symmetry in wallpaper patterns. Journal of Vision 2014;14(10):1430. doi: 10.1167/14.10.1430.
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Symmetry is a striking visual attribute that occurs in nature and has been used by artists since the Neolithic age. All two-dimensional periodic patterns can be mathematically associated with one of 17 wallpaper symmetry groups, each containing unique combinations of Euclidean plane isometries (translation, rotation, reflection and glide). Recent behavioral work has shown that pattern similarity judgments by human observers are to a large extent driven by this group structure (Clarke et al., Symmetry, 2011). How are these perceptual and mathematically defined similarities between wallpaper groups represented in human neural activity? We investigated this question with Visual Evoked Potentials. Our experimental design allowed us to clearly separate the configural response to the symmetry from the evoked response to local contrast change. We presented patterns associated with five different wallpaper groups that have different rotation isometries, but are otherwise equivalent (P1,P2,P3,P4,P6). Participants (n=9) performed a contrast-change detection task that was orthogonal to judging pattern similarities. They all elicited a configural response, but there were differences in the symmetry response dynamics and waveforms between the groups, with at least three qualitatively distinct types of neural responses. P3, a group that human observers found difficult to categorize (Clarke et al., Symmetry, 2011), had the weakest configural response of the five wallpaper groups tested, suggesting a correspondence between behavioral and neural data. We also found systematic group-level differences in the latency of the symmetry response, such that simpler groups with fewer rotation isometries (P1,P2) elicited an earlier response than groups with more rotation isometries (P4,P6). The weak response to P3 echoes low perceptual salience, while prolonged latency for patterns with more rotation isometries may reflect processing costs associated with wallpaper group complexity. Future work will explore and distinguish the ways in which both types of information are represented in the brain.
Meeting abstract presented at VSS 2014
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