View article

When perceiving symmetry, an ERP component known as the Sustained Posterior Negativity (SPN) is produced. From around 250ms, amplitudes in posterior electrodes are more negative for symmetrical than random patterns (Makin et al., 2012). This component is thought to be spread over both hemispheres. A role for the corpus callosum has also been highlighted when symmetrical patterns are presented at fixation (Herbert & Humphrey, 1996). We tested this callosal hypothesis by measuring SPN response to peripheral stimuli. Twenty-four participants were presented with a reflection and a random dot pattern. Patterns were both either light or dark red in different trials, and participants made a colour discrimination. Patterns were presented to a single hemisphere by simultaneously positioning one to the left of the fixation cross and the other to the right. We contrasted trials where symmetry was on the left and …