Abstract
Visual regularity activates a network of brain regions in the extrastriate cortex. Previous EEG studies have found that this response scales parametrically with proportion of symmetry in symmetry + noise displays. The parametric symmetry response happens in many tasks, but it is enhanced during active regularity discrimination. However, the origins and time course of this selective enhancement are unclear. Here we answered remaining questions with new source dipole analysis. As assumed, the parametric symmetry response found at the sensor level was generated by a pair of dipoles in the left and right extrastriate cortex. This bilateral activity was itself enhanced during regularity discrimination. However, we identified a third, and later, symmetry response in the posterior cingulate during regularity discrimination. Unlike the extrastriate response, this previously unknown activation only indexes strong, task relevant regularity signals. This clarifies the neural circuits which mediate the perceptual and cognitive aspects of symmetry discrimination.
Highlights
Visual regularity activates a network of brain regions in the extrastriate cortex
Beyond the role that symmetry plays in terms of perceptual organization, its evolutionary relevance is key in that symmetry is more aesthetically pleasing and relevant for mate selection[10,11,12,13,14,15,16], potentially due to perceptual fluency[17]
The sustained posterior negativity (SPN) wave measured at posterior electrodes scales with PSYMM in several tasks, but is selectively enhanced during regularity discrimination[24]
Summary
Visual regularity activates a network of brain regions in the extrastriate cortex. Previous EEG studies have found that this response scales parametrically with proportion of symmetry in symmetry + noise displays. The parametric symmetry response happens in many tasks, but it is enhanced during active regularity discrimination. The parametric symmetry response found at the sensor level was generated by a pair of dipoles in the left and right extrastriate cortex This bilateral activity was itself enhanced during regularity discrimination. This previously unknown activation only indexes strong, task relevant regularity signals This clarifies the neural circuits which mediate the perceptual and cognitive aspects of symmetry discrimination. Visual symmetry can affect performance in secondary tasks[8,9] This suggests symmetry itself is processed automatically, even when it is not task relevant. The extrastriate response is similar whether symmetry is task relevant or not, but it is sometimes enhanced during regularity discrimination tasks[24]. Other work has isolated the symmetry response in odd harmonics of the SSVEP34
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