We cannot by volition prevent the sensory nerves from transmitting the impulses caused by external relations. For example, we cannot by volition prevent hearing a sound. But these actions may be guided, stimulated and concentrated by volition. If there are several simultaneous sound relations in progress in a room occupied by a listener, he may by volition concentrate upon the sound from one source, as the voice of one person among many, and not even hear the others.
This is what we mean by voluntary control of the organs of sense. There may be many objects in a field of view, but the eye may by volition be directed to only one small object, the others not even being seen. But there are also conditions under which the sensory nerves do not appear to transmit external relations, even involuntarily, or, if the transmission occurs, it is entirely without effect. For example, sound relations, though very intense and in close proximity to a sleeper, may be entirely unheard.
These considerations lead us to several important conclusions:
1. That in abnormal conscious states the control of the sensory tracts is involuntary.
2. That in normal states the control of the sensory tracts is chiefly voluntary, but there is always a certain amount of involuntary action.
3. That there may, therefore, be both voluntary and involuntary action at the same time.
4. That there is the possibility of the simultaneous existence in the same individual of an abnormal and a normal conscious state.
5. That the simultaneous existence of the normal and abnormal conscious states, would be most likely to occur, if ever, at the instant when the sensory tracts change from voluntary to involuntary or from involuntary to voluntary action.
When external relations, transmitted by involuntary sensory action, knock for admittance at the door of the sleeping cerebrum and generate a normal brain activity, there may already have been in existence an abnormal conscious state—a dream, caused, either by a previous unsuccessful effort at normal brain stimulation, or by some other cause, and maintained by involuntary control.
We have defined consciousness as knowledge of the existence of self and of the Universe. We have found that it exists only in connection with brain or nerve activity. Hence, when these activities cease, conscious states will cease.
***Excerpt from Charles John Reed: The Law of Vital Infusion and the Phenomenon of Consciousness