Electrophysiological dynamics of false belief understanding and complementation syntax in school-aged children: Oscillatory brain activity and event-related potentials

•Parieto-occipital beta power distinguished belief from complementation conditions.•Parieto-occipital late slow waves (600–900 ms) showed the same divergence.•The false-belief condition, among the four, had the lowest behavioral accuracy.•Together, results suggest false complementation is not redundant to false belief. A large body of research in developmental psychology has been devoted to the ongoing debate over which aspects of language are fundamental to false belief understanding (FBU). A key proposal from de Villiers and colleagues proposes the essential role of complementation syntax in FBU development. The current study, using scalp electroencephalography (EEG), addressed one opposing hypothesis purporting that complementation is redundant to FBU by characterizing the electrophysiological correlates of FBU and complementation syntax in school-age children. Time–frequency decomposition showed robust parieto-occipital low beta (12–16 Hz) power reduction in the belief versus complementation conditions. This divergence was also supported by event-related potentials (ERPs), with parieto-occipital late slow waves around 600 to 900 ms distinguishing belief and complementation conditions. The false belief condition generated the lowest behavioral response accuracy, suggesting that it is the most challenging condition. Together, the current findings provide evidence showing that complementation is not redundant to FBU.