Unlike many modern psychologists, he felt the field should encompass paranormal phenomena and mystical experiences. As well as writing one of the great studies of mystical experiences, The Varieties of Religious Experience, he self-experimented with psychoactive substances such as nitrous oxide and ether. (From this perspective, a mystical experience is an experience of heightened awareness, in which the world becomes more vivid and beautiful, and there is a sense of oneness and bliss, as well as a sense of meaning and revelation.)