Shared symmetry detection with divergent temporal dynamics in marmosets and humans

Symmetry is a fundamental organizing principle of mid-level vision, yet which aspects of human symmetry processing are shared across primates remains unclear. 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, lacking the sustained late component prominent in humans. This dissociation suggests that 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, particularly for rotation. These findings establish marmosets as a tractable model for symmetry processing and open a path to intracortical recording in accessible extrastriate cortex.