| Both a book and a theoretical model by Ken Wilber. In my opinion, a work of genius. An important part of transpersonal psychology. Also a really big book that I don't pretend to understand completely.
The "spectrum" is a synthesis of, and addition to, several models of the various levels of consciousness and spiritual development. It takes many Western models, including Maslow's Heirarchy of needs, Freud's oral and anal phases, and even things like the Cabbalah. It takes eastern models from India, Japan, and China, including Zen.
He breaks it all down into a circle, leading from birth to normality to sanity, from uroboric consciousness to egoic consciousness to unity consciousness. A good explanation of why "enlightenment" should be plural and the ego is not something evil, just a stage.
The whole thing is way too complicated to get into here, but I suggest you read the book if you have some time. More concise explanations are also found in The Atman Project and A Brief History of Everything. | 
