During the 1960s Maslow founded with Stanislav Grof, Viktor Frankl, James Fadiman, Anthony Sutich, Miles Vich and Michael Murphy, the school of transpersonal psychology. Maslow had concluded that humanistic psychology was incapable of explaining all aspects of human experience. He identified various mystical, ecstatic, or spiritual states known as "peak experiences" as experiences beyond self-actualization. Maslow called these experiences "a fourth force in psychology", which he named transpersonal psychology. Transpersonal psychology was concerned with the "empirical, scientific study of, and responsible implementation of the finding relevant to, becoming, mystical, ecstatic, and spiritual states" (Olson & Hergenhahn, 2011).