Corrigendum: A Review of Possible EEG Markers of Abstraction, Attentiveness and Memorisation in Cyber-Physical Systems for Special Education - Dimitrova, Maya; Wagatsuma, Hiroaki; Krastev, Aleksandar; Vrochidou, Eleni; Nunez-Gonzalez, J. David (Frontiers in Robotics and AI, 2021)