During the sleep cycle the subconscious mind processes the information that was acquired throughout the day. It will not respond to additional information, because it has to put the old information in places.
Sleep learning is for lazy people. Forget about all these new technological devices that are fulling people regarding sleep learning.
My philosophy is that it is best not to touch your dreams. Let go of conscious control of them - Lucid dreaming. (I can foresee a wave of disagreement about this with me from a lot of photoreaders). You may set goals for your subconscious to solve, or ideas to be found. But do not control or interferer with it. Dreams or sleep cycles are for some reason we may not yet know. It is a time to let go and allow your mind to function on its own, to heal the body and sort the information in its places.
Well thats what I think.
[This message has been edited by Ivan (edited January 26, 2004).]