The representation of symmetry in multi-voxel response patterns and functional connectivity throughout the ventral visual stream

Abstract

Several computational models explain how symmetry might be detected and represented in the human brain. However, while there is an abundance of psychophysical studies on symmetry detection and several neural studies showing where and when symmetry is detected in the brain, important questions remain about how this detection happens and how symmetric patterns are represented. We studied the representation of (vertical) symmetry in regions of the ventral visual stream, using multi-voxel pattern analyses (MVPA) and functional connectivity analyses. Our results suggest that neural representations gradually change throughout the ventral visual stream, from very similar part-based representations for symmetrical and asymmetrical stimuli in V1 and V2, over increasingly different representations for symmetrical and asymmetrical stimuli which are nevertheless still part-based in both V3 and V4, to a more holistic representation for symmetrical compared to asymmetrical stimuli in high-level LOC.This change in representations is accompanied by increased communication between left and right retinotopic areas, evidenced by higher interhemispheric functional connectivity during symmetry perception in areas V2 and V4.

A dual role for shape skeletons in human vision: perceptual organization and object recognition

“…The finding that V3 represents shape skeletons is consistent with human neuroimaging studies showing its involvement in perceptual organization (Sasaki, 2007). Indeed, V3 has been consistently implicated in creating shape percepts (Caplovitz, Barroso, Hsieh, & Tse, 2008;McMains & Kastner, 2010;Montaser-Kouhsari, Landy, Heeger, & Larsson, 2007) and is the earliest stage of the visual hierarchy where symmetry structure has been decoded (Keefe et al, 2018;Sasaki, Vanduffel, Knutsen, Tyler, & Tootell, 2005;Van Meel, Baeck, Gillebert, Wagemans, & Op de Beeck, 2019). But how might shape skeletons arise in V3?…”

The extrastriate symmetry response can be elicited by flowers and landscapes as well as abstract shapes

“…The extrastriate symmetry response increases with the degree of regularity in wallpaper patterns ( Kohler, Clarke, Yakovleva, Liu, & Norcia, 2016 ) and the proportion of symmetry in symmetry + noise displays ( Keefe et al., 2018 ; Sasaki et al., 2005 ). Recently, van Meel, Baeck, Gillebert, Wagemans and Op de Beeck (2019) found that the distinction between symmetrical and asymmetrical dot patterns can be reliably decoded from patterns of voxel activations in LOC. Transcranial magnetic stimulation work provides converging evidence: For example, Bona, Herbert, Toneatto, Silvanto and Cattaneo (2014) found that disruption of LOC selectively impairs symmetry discrimination (see also Bona, Cattaneo, & Silvanto, 2015 ; Cattaneo, Mattavelli, Papagno, Herbert, & Silvanto, 2011 ).…”

Electrophysiological responses to regularity show specificity to global form: The case of Glass patterns

“…More recent psychophysical (Kelly et al, 2001; Kurki & Saarinen, 2004; Seu & Ferrera, 2001) and neuroscientific results (Ostwald et al, 2008;Pei et al, 2005) corroborate this theory. Functional MRI in monkeys and humans has identified symmetry-related activations in areas V4 and LOC but not areas V1 or V2 (Chen et al, 2007;Keefe et al, 2018;Kohler et al, 2016;Sasaki et al, 2005;Tyler et al, 2005;Van Meel et al, 2019). Van Meel et al (2019) suggest a gradual change from part-base coding in areas V1-V2, to computation of more complex features in V4, to final global symmetry representation in LOC.…”

“…It has negative amplitude and is generated by neurons in the extrastriate cortex and lateral occipital complex (LOC; Makin et al, 2016;Rampone, Makin, Tatlidil, & Bertamini, 2019). The SPN is a well-characterised neural signal, and its interpretation is consistent with fMRI (Chen, Kao, & Tyler, 2007;Keefe et al, 2018;Kohler, Clarke, Yakovleva, Liu, & Norcia, 2016;Sasaki, Vanduffel, Knutsen, Tyler, & Tootell, 2005;Tyler et al, 2005;Van Meel, Baeck, Gillebert, Wagemans, & Op de Beeck, 2019) and TMS evidence (Bona, Cattaneo, & Silvanto, 2016;Bona, Herbert, Toneatto, Silvanto, & Cattaneo, 2014;Cattaneo et al, 2014;Cattaneo, Bona, & Silvanto, 2017). Makin et al (2016) tested specific predictions of the holographic model.…”