We shall see later that the problems connected with Prevision and Postvision are also, if not completely explained, at least rendered less utterly incomprehensible by the introduction of the higher space hypothesis.
With the third class of clairvoyant phenomena is closely associated that group of facts known as "Phantasms of the Living, of the Dying, and of the Dead."
Certain aspects of the dream state, again, seem to be related to clairvoyance at a distance and are conveniently dealt with here.
Let us follow up the idea of a four-dimensional vehicle and see what light, if any, it throws on these questions.
Let us suppose that the four-dimensional vehicle becomes detached from, and loses touch with, the three-dimensional physical body during unconsciousness; or rather that unconsciousness is due to this detachment.
It follows that the "Ego" embodied in this four-dimensional vehicle can no longer receive impressions through the three-dimensional sense organs and that it is wholly dependent for communication with the outside world on those which belong to the four-dimensional vehicle. The nature of the impressions received will depend on the degree of development of these organs.
If they are completely undeveloped the Ego will be utterly oblivious of its surroundings, whereas if they are well developed the reverse will be the case and we may suppose the Ego to be as fully cognizant of the surrounding world as we are in ordinary waking life. It is interesting to compare with this the statements of those who claim to have consciously explored the "Astral plane" or four space world. They often describe sleepers as being present, but "in a brown study." Compare also the statement often found in communications purporting to emanate from discarnate personalities to the effect that, "We have seen so-and-so, but do not know whether he is dead or not."
Of course, it by no means follows that it will be possible, even under these latter conditions, to remember in waking life the impressions received during unconsciousness. On the contrary we should expect this to be the exception rather than the rule.
In their passage from sense organ to consciousness the impressions received will, ex hypothesi, not pass through the physical brain and the memory centres with which they become associated may be located in a position which is inaccessible to consciousness when embodied in the physical vehicle.
It would be possible, though not perhaps absolutely necessary, to account on these lines for the impression which most people have sometimes had, of apparently "remembering" a place which they have certainly never visited previously in waking life. They might, however, on this theory, have done so in sleep.