Peter J. Kohler^1,4 (), Amirhossein Asadian^1,2,4, Dirk B. Walther^3,4, Liya Ma^1,4; ¹Department of Psychology, York University, ²Department of Biology, York University, ³Department of Psychology, University of Toronto, ⁴Centre for Vision Research, York University

Symmetry is a biologically significant mid-level visual feature that has been studied for more than a century. Brain imaging has revealed reliable responses to many symmetry types and provided an emerging understanding of the temporal dynamics and brain regions involved. This work has mostly been done in humans, but macaque monkeys have similar responses in homologous brain regions (Audurier et al., 2022). Here we present the first study of symmetry responses in another non-human primate species, the common marmoset. Marmosets have structurally and functionally similar visual cortices to those of humans and macaques, but comparatively small brains with smooth cerebral cortices that enable layer-specific intracranial recordings within homologues of human visual areas that would be hidden in sulci in macaque brains. As a first step in that direction, we recorded EEG data from 32-channel surface grids chronically attached to the skulls of 3 marmosets, and measured symmetry responses using a Steady-State Visual Evoked Potentials (SSVEPs) paradigm well-documented with human participants (Norcia et al., 2002). Our stimuli were a class of regular textures known as wallpaper groups that each contain unique combinations of symmetries. We generated large (24º) textures from two groups that produce robust responses in both humans and macaques: PMM, which contains reflection symmetry, and P4, which contains four-fold rotation symmetry. Our paradigm made it possible to isolate and identify both symmetry-specific brain responses and low-level image-update responses, in the odd and even harmonics of the stimulation frequency (Kohler et al., 2016). Both groups produced robust image-update responses, as well as reliable symmetry responses within posterior electrodes, with similar temporal dynamics to those found in humans. Our findings show that marmosets produce responses to reflection and rotation symmetry that can be measured with SSVEPs, and open the door to intracranial recordings of spiking activity and local field potentials.

Acknowledgements: This research was undertaken thanks in part to funding from the Vision: Science to Applications, supported by the Canada First Research Excellence Fund. Additional support was provided by a Natural Sciences and Engineering Research Council of Canada Discovery Grant awarded to PJK.