Abstract
Symmetry is ubiquitous in the natural world. Numerous investigations, dating back over one hundred years, have explored the visual processing of symmetry. However, these studies have been concerned with mirror symmetry, overlooking radial (or rotational) symmetry, which is also prevalent in nature. Using a visual search paradigm, which approximates the everyday task of searching for an object embedded in background clutter, we have measured how quickly and how accurately human observers detect radially symmetric dot patterns. Performance was compared with mirror symmetry. We found that with orders of radial symmetry greater than 5, radial symmetry can be detected more easily than mirror symmetry, revealing for the first time that radial symmetry is a salient property of objects for human vision.
Highlights
Symmetric structures exist throughout the biological world
A further increase in efficiency was revealed for seventh-order radial- compared to mirror-symmetric targets, t(9) 1⁄4 4.65, p < .001), that is, seventh order radially symmetric patterns were detected more than mirror symmetry patterns
Our data show that (a) search times are dependent on the number of distractors, that is, they are serial, consistent with Olivers and van der Helm’s (1998) finding that symmetry detection requires selective attention; (b) as the order of radial symmetry increases, search times decrease; (c) mirror-symmetric patterns are detected with higher efficiency than third-order radial patterns, with equal efficiency as fifth-order radial patterns, and with lower efficiency than seventh-order radial patterns
Summary
Symmetric structures exist throughout the biological world. The visual perception of symmetry is an important biological function, enabling animals to detect the presence and type of a variety of biological objects in the scene. While two electrophysiological studies, using event-related potentials, have revealed that humans are sensitive to both mirror and radial symmetry (Bertamini & Makin, 2014; Makin, Wilton, Pecchinenda, & Bertamini, 2012), radial symmetry ( referred to as rotational symmetry) has not been systematically studied in a visual search paradigm. This in spite of the fact that like mirror symmetry, radial symmetry is ubiquitous in nature: The flowers and starfish in Figure 1 are exemplars. We measured the ability of humans to visually detect a radially symmetric pattern and compared our results with the detection of mirror symmetry
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