Abstract
Animal species from across the phylogenetic tree are highly sensitive to visual symmetries in their surroundings. In humans, psychophysical experiments have demonstrated that symmetry is an important cue to perceptual organization, and brain imaging experiments have measured robust and precise responses to different types of symmetry in visual brain areas. Is sensitivity to symmetry innate or does it arise over visual development due to exposure to symmetries in the visual environment? Leverage can be gained on this question by testing whether infants display sensitivity to symmetry – if not, sensitivity clearly arises at a later stage of visual development. There is behavioral evidence for reflection symmetry sensitivity in infants, primarily using preferential-looking paradigms (e.g., Humphreys & Humphreys, 1989). Here we used high-density EEG to measure symmetry responses from 3-month-old infants. Our stimuli were a class of regular textures known as wallpaper groups – a set of 17 unique combinations of symmetry types. We focus on two groups that prominently feature reflection and rotation symmetries, respectively. We use a Steady-State Visual Evoked Potentials (Norcia et al., 2015) paradigm that allows us to isolate brain responses that are driven by the symmetries in our textures (see Kohler et al., 2016). We see evidence of symmetry-specific responses over visual cortex which are broadly similar to those we observe in adults. Importantly, we see such responses for both reflection and rotation. We are unaware of any prior evidence of sensitivity to rotation symmetry in infants. Reflection is prominent in the visual world of infants and tied to important stimuli (e.g., faces). This is not true for rotation. The presence of brain responses to rotation symmetry at this early stage of visual development seems to offer especially strong evidence against the hypothesis that symmetry sensitivity arises due to exposure to symmetries in the visual world.