One of the most extensive study of the characteristics of altered states of consciousness was made by psychologist Charles Tart in the 1960s and 1970s. William James is usually credited with popularizing the idea that human consciousness flows like a stream.
The most thorough account of the spiritual approach may be Ken Wilber's book The Spectrum of Consciousness, a comparison of western and eastern ways of thinking about the mind, Ken Wilber described consciousness as a "spectrum" with ordinary awareness at one end, and more profound types of awareness at higher levels. The mystical psychiatrist Richard Maurice Bucke distinguished between three types of consciousness: Simple Consciousness, awareness of the body, possessed by many animals; Self Consciousness, awareness of being aware, possessed only by humans; and Cosmic Consciousness, awareness of the life and order of the universe, possessed only by humans who are enlightened. According to Tart, "Anything that we are aware of at a given moment forms part of our consciousness, making conscious experience at once the most familiar and most mysterious aspect of our lives." MMY has recorded a lecture describing seven states of consciousness, which follows the description according to the yoga tradition of India. MMY's description of seven states agrees with Swami Rama and Swami Sivananda Saraswati. "Wilber, the father of transpersonal psychology, with brilliant clarity, depth, and synthesis explores the nature of consciousness through the seeing of the worlds greatest sages. This tour de force of the mapping of transcendental awareness is both brilliantly conceived and delivered by one of the foremost thinkers of our time. Anyone on the path of enlightenment can not afford to miss studying and assimilating the non-dual seeing of Ken Wilber." - Edward Plotkin Work cited: 'The Spectrum of Consciousness' By Ken Wilber Quest Books, 1993 pp. 3-16; 52 'States of Consciousness' by Charles Tart p. 95
