Charles Tart on Altered States

"Because we approach spiritual questions--for example, the question of our destiny after death--only from the perspective of ordinary states of consciousness, it is not surprising that the answers we get are only distorted, pale reflections of reality. We have become so blinded by abstract verbal statements about spiritual truths that we miss the chance to verify those truths for ourselves by direct expercience. Hence the prevalent spiriual dissatisfaction of our times."
-Charles T. Tart, Ph.D.

That's from a book called What Survives? edited by Gary Doore. More stuff on altered states of consciousness can be found on TASTE - The Archives of Scientists' Transcendent Experiences.