Neural processing of illusory and real contours revealed by high-density ERP mapping

Event-related potential (ERP) studies have shown that responses to illusory (IC), as compared to no contours (NC), may differ within 200 ms following stimulus presentation. However, whether these responses reflect the modulation of similar, or the activation of distinct brain regions has never been assessed. Using ERP map series and source localisation analyses, we compared early responses (0-200 ms) to IC and NC, as well as to real contours (RC). Although IC displayed higher field strength during the NI component, topographical analyses showed a similar sequence of stable field configurations in all conditions. Source localisation applied to the NI map revealed bilateral activation of lateral-occipital regions. These results suggest that both IC and RC processing modulate a common network associated with filling-in processes and figure-ground segregation.