Shared symmetry detection with divergent temporal dynamics in marmosets and humans

Which features of human perception are shared across the primate lineage, and which are specializations, is a central question in the biology of cognition. fMRI studies have located symmetry-selective cortex in macaques [1,2], and preliminary intracortical recordings point to symmetry-sensitive neurons in V2-V4 [3]. Yet no study has measured symmetry responses in non-human primates (NHPs) with the same non-invasive electrophysiology used in humans. Thus, it remains unknown whether NHPs respond to symmetry with dynamics that match those in humans. Using steady-state visual evoked potentials during passive viewing, we compared responses to two well-matched wallpaper groups, double reflection (PMM) and four-fold rotation (P4), in common marmosets and humans, using identical stimuli. Marmosets showed robust reflection-symmetry responses comparable in relative magnitude, temporal dynamics and scalp distribution to those of humans. Rotation responses were also reliable but transient, without the sustained late component prominent in humans. This dissociation suggests that fast, feedforward computations underlying symmetry detection are conserved across primates, whereas sustained processing that elaborates symmetry representations, likely recurrent or feedback in origin, is reduced in marmosets and most clearly for rotation. These findings identify a point of divergence for primate visual processing and are consistent with the emerging view that marmosets rely less on cortical feedback than macaques or humans. Our approach establishes marmosets as a tractable model for symmetry processing and opens a path to intracortical recording in easily accessible extrastriate cortex.