12/16/2023 0 Comments Variant perception definition![]() Symmetry detection is fast and noise resistant (Barlow & Reeves, 1979 Carmody, Nodine, & Locher, 1977 Wagemans, Vangool, & Dydewalle, 1991). Although the human visual system can detect all types of symmetries, reflectional symmetry has been shown to be the most salient (Julesz, 1971 Palmer & Hemenway, 1978 Royer, 1981), particularly if the axis is vertical (Friedenberg & Bertamini, 2000 although see Wenderoth, 1994). Patterns can also contain combinations of these transformations, and classifications of these exist for friezes and wallpaper patterns (for an overview, see Wagemans, 1997). The main rigid transformations that generate symmetry are reflection (which creates what is also sometimes referred to as mirror or bilateral symmetry), rotation, and translation (i.e. From a geometrical standpoint, symmetry is defined as a form of regularity possessed by a mathematical object and is characterized by the operations that leave the object invariant. Fluent perception of symmetry is thus important for fast, accurate perceptual organization, particularly for figure–ground segmentation. Many natural and created objects are symmetric along at least one axis. Symmetry is pervasive in our environment. Therefore, under everyday viewing conditions, symmetry perception engages a relatively broad cortical network that is not constrained by low-level inputs. In conclusion, while our findings at threshold support models that propose an important contribution of low-level mechanisms to symmetry perception, at suprathreshold these low-level contributions do not persist. However, interactions between symmetry and contrast type were not observed. ![]() Sustained posterior negativity, a symmetry-sensitive ERP component, was observed in all conditions and showed the expected dependence on symmetry. The subsequent ERP experiment was run at high contrasts to assess processing of symmetry in suprathreshold conditions. These findings are in line with distinct contrast sensitivity functions for color and luminance, with color providing low-frequency information useful for symmetry detection and luminance providing high-frequency information useful for detection of detail. Stimuli at isoluminance were associated with a large bias toward symmetry, achromatic stimuli introduced the opposite bias, and stimuli containing a balance of both color and luminance were perceived without bias. Participants then judged whether a pattern was symmetric or random. In the psychophysical experiment, pattern contrast was fixed at individual symmetry-discrimination threshold. To test for potential influences of early low-level mechanisms on symmetry perception, we used isoluminant, achromatic, and combined (color + luminance) patterns in a psychophysical and an event-related-potential (ERP) experiment. Perception of visual symmetry is fast and efficient and relies on both early low-level and late mid- and high-level neural mechanisms.
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