I have found exploration of this in several spiritual paths...from the Japa meditation in Wayne Dyer's "Getting into the Gap" to the practice in sound from the Centering portion of "Zen Flesh, Zen Bones", to the techniques for lucid dreaming, and to the shamanistic practice of "getting behind" things into the true world.
It also seemingly occurs in physics in the very small space between linearity and turbulence, and the same in the behaviour of an audio filter in the tiny space just prior to self-oscillation.
Dyer recommends looking into the space(s) between letters in a phrase. Centering recommends following a sound down into silence, and examining the point at which sound actually meets silence. The decay of a prayer chime is excellent for this. Shamanism relates much of the same; becoming aware of the enormous, silent place when you are in between breaths, immediately after orgasm, the emptiness after the elimination of waste, etc. The place between release and the building of new tension.
Centering:
16. In the beginning and gradual refinement of the sound of any letter, awake.
18. Intone a sound audibly, then less and less audibly as feeling deepens into this silent harmony.
We are surrounded by these gaps, by these transitory states, these fringe conditions. Seek them, and the secrets they convey.
Also, to become aware of the fifth element, Space, or "Volume".
The medium in which all things arise. Become aware of the space between yourself and a cloud. Find the spaciousness of the spirit side through meditation, and carry it into everyday awareness.
