The book presents selected works of the outstanding Russian physiologist and psychologist Ivan Mikhailovich Sechenov (1829-1905). In addition to the classic work “Reflexes of the Brain” (1863), which opened the era of objective psychology, the book includes the scientist’s later works, in which he turns to psychophysiology and the theory of knowledge, analyzing a wide range of phenomena - from unconscious reactions in animals to higher forms of perception in humans . K. A. Timiryazev, speaking about the incredible breadth of the range of interests of his teacher and the significance of his contribution to Russian science, noted: “If we add to this the brilliant, remarkably simple, clear form in which he clothed his thoughts, then the wide influence will become clear , which he had on Russian science, on Russian thought, even far beyond the boundaries of his audience and his specialty.”