This is the domain of cicads, subliminal messaging, etc. And so, some conclude, alert-awareness isn't actually necessary. That is possible, but not proper, I think. The perceptual bias of territorial and power structure dominance is inappropriate when applied here. It is wrong to extend to such sub or between activites of consciousness any quality of being isolatedly independent, or as being lesser or inferior or sub-stantial, in any way.
Dynamic activities go on there all the time.
We rely on them. We depend on them. It's that part of our information processing which we turn to each and every instant of alert-awareness, without break, without cessation. It's not off-line or hidden, but running forever in accessible parallel. So the better term is autonomic consciouness , not sub anything.