CONSCIOUSNESS in its widest sense denotes mental ex perience of every kind. In this sense of the term consciousness may be described as the subject matter of psychology (q.v.), and psychology might be defined as the science of consciousness. Very frequently, however, the term is used in the sense of self consciousness, or of what is in the focus of consciousness, or at least in the margin of consciousness. It is then contrasted with the sub-conscious and the unconscious, etc. (See ABNORMAL PSY CHOLOGY, and PSYCHOANALYSIS.) Physiology of Consciousness.—Physiologists and most psy chologists assume that physical awareness is wholly dependent upon some definite bodily structure or structures. Various theories exist as to the identity of this bodily organ of consciousness. One theory holds that each atom of the physical body possesses an inherent attribute of consciousness. If each atom, or, in later forms of this theory, each cell of the body emanates its own consciousness, then the "self" must actually consist of an amal of all these tiny units of awareness. Experimental evidence is against this theory, since physical consciousness seems to disappear from any part of the body disconnected from the central nervous system.
A second theory assumes that there exist, in the brain, special nerve cells capable of producing consciousness whenever acti vated. There is no physical evidence for the existence of such special consciousness cells.
A third theory seeks to identify consciousness with some aspect of the simple nerve impulse. There are two lines of evidence against this theory. First, the physical phenomena most closely corresponding with consciousness do not occur within individual nerve cells, but rather between the individual cells joined to gether in any reflex-arc system. Some of these phenomena are inhibition, irreversability of direction of propagated disturbances, fatigue, marked susceptibility to drugs, conflict and mutual facili tation of impulses, marked delay of reflex conduction, after dis charge and summation of impulses. Second, identical nerve cells are activated in producing very dissimilar states of consciousness; and different nerve cells are stimulated to produce identical elements of consciousness.
The psychonic theory, based on the correspondences between consciousness and inter-neuronic phenomena, suggests that con sciousness occurs each time any unit of junctional tissue between individual neurones is energized. Units of junctional tissue are termed psychons, and each psychonic impulse is regarded as a single unit of physical consciousness. This theory is now under experimental investigation.
See W. M. Marston, "The Psychonic Theory of Consciousness," Journal of Abnormal and Social Psychology (July 1926).
(W. M. M.)