Symmetry Perception and Psychedelic Experience

Abstract

This review of symmetry perception has six parts. Psychophysical studies have investigated symmetry perception for over 100 years (part 1). Neuroscientific studies on symmetry perception have accumulated in the last 20 years. Functional MRI and EEG experiments have conclusively shown that regular visual arrangements, such as reflectional symmetry, Glass patterns, and the 17 wallpaper groups all activate the extrastriate visual cortex. This activation generates an event-related potential (ERP) called sustained posterior negativity (SPN). SPN amplitude scales with the degree of regularity in the display, and the SPN is generated whether participants attend to symmetry or not (part 2). It is likely that some forms of symmetry are detected automatically, unconsciously, and pre-attentively (part 3). It might be that the brain is hardwired to detect reflectional symmetry (part 4), and this could contribute to its aesthetic appeal (part 5). Visual symmetry and fractal geometry are prominent in hallucinations induced by the psychedelic drug N,N-dimethyltryptamine (DMT), and visual flicker (part 6). Integrating what we know about symmetry processing with features of induced hallucinations is a new frontier in neuroscience. We propose that the extrastriate cortex can generate aesthetically fascinating symmetrical representations spontaneously, in the absence of external symmetrical stimuli.

Perceptual organization and visual awareness: the case of amodal completion

“…Global completion, is based on maximum symmetry. In contrast to good continuation, symmetry produces strong responses only in higher-order regions, especially V4 and LOC (e.g., Sasaki et al, 2005 ), symmetry-based grouping was found to require visual awareness ( Devyatko and Kimchi, 2020 ; but see, Makin et al, 2023 ), and the role of symmetry in perceptual organization is not entirely clear because of its interaction with other grouping factors ( van der Helm, 2015 ). For example, a number of researchers argue that grouping by other factors precedes and facilitates grouping by symmetry (see for discussion Machilsen et al, 2009 ).…”

The extrastriate symmetry response is robust to alcohol intoxication.

“…The parametric SPN response was evident in 5 tasks (from 5 different groups of 26 participants) but selectively enhanced in the regularity task (left). Figure from Makin et al (2023).…”

“…Visual symmetry contributes to perceptual organisation and object formation (Bertamini et al, 2018;Makin et al, 2023). Psychophysical research demonstrates that the detection of symmetry is fast and noise tolerant.…”

Putting things into perspective: Which visual cues facilitate automatic extraretinal symmetry representation?

“…Symmetry is also a gestalt grouping principle that aids grouping and figureground segmentation (Koffka, 1935;Wagemans et al, 2012). Many psychophysical studies have investigated symmetry perception in humans (Barlow & Reeves, 1979;Treder, 2010), while the brain response to symmetry has been studied extensively in the last 20 years (for recent reviews see Bertamini et al, 2018;Cattaneo, 2017;Makin et al, 2023). Functional MRI studies have found that visual symmetry activates a network of regions in the extrastriate cortex, centred on object sensitive areas V4 and the Lateral Occipital Complex (Keefe et al, 2018;Kohler et al, 2016;Sasaki et al, 2005;Tyler et al, 2005;Van Meel et al, 2019).…”