For example, the hypnagogic warp before sleep lasts but a few seconds for most people in our society, yet its activity determines the quality of the dream phases that follow it. Tibetan dream yogis learn to control the hypnagogic by practicing certain rituals and are able to exercise considerable control over the organization of experience during sleep. For this reason, the ethnographer should learn to discern shifts in states of consciousness in informants and ascertain what, if any, ritual activity has been positioned so as to mediate the change of their internal state. Rituals are often symbolically rich events. Moreover, rituals frequently incorporate a variety of drivers that may account in some measure for the rituals' efficacy.
Drivers are ritual elements that evoke specific neurophysiological effects.
They may be fairly gross in their form, such as drumming, dancing, injestion of psychotropic drugs, sweat baths, stressful ordeals, flickering lights, chanting, fasting, special diets, etc., or they may be relatively subtle in form, such as intense concentration upon the breath, upon eidetic imagery, or upon a burning question. Drivers are very often universal in their essential form. The ethnographer should also be aware that while a ritual activity may be a necessary condition for an intended experience, and perhaps even include a profusion of drivers, it is unlikely to be a sufficient condition. A ritual is a totality that is itself an element in a greater play. A ritual is part of a whole, a context.