This document describes information processing in the brain, from sensation and perception to conscious and unconscious processing, reaction, and feedback. It also discusses perception in more detail, including how we perceive the world and the potential illusions that may arise, especially in relation to flying. Finally, the text addresses attention and its limitations, as well as how attention, perception, and information processing relate to pilot competencies and flight safety, including situation awareness, decision-making, and workload management. The text provides a theoretical basis for more applied chapters.