CONSCIOUSNESS (Ger. Bewusstsein; Fr.. conscience; lt. conscienza) is the term by which psychology distinguishes one of the two great categories into which experience falls, viz., mental experience, from the other, physical experience. The one division, mental experi ence, includes all facts that may be construed as subjective, the other division all facts that are considered by the uncritical mind to be objective. From time immemorial the .former order of experiences has been customarily held to constitute a series of immaterial sequences that in their totality construct a personal life history; the latter has just as stoutlfy been looked upon as forming a causal chain o events in a material world external to but reflected by the mental series. This picture of mind in re ciprocal relationship with an external world portrays the naive dualism of common-sense thought.
Regarded analytically consciousness brealcs up into a series of processes producing. sense percepts, images of memory and imagination, associations, judgments, reasonings, feelings, emotions and volitions. Regarded from the standpoint of their totality these processes of consciousness constitute an individual mental history or ntind. The objective facts above al luded to fortn the content of consciousness, forming in their entirety the world of external realities, a world distinguished into the two great subdivisions of living and non-living nature.
There is probably no term in the nomen clature of psychology that is subject to such vagueness of reference and ambiguity of mean ing. Professor Ward has declared it to be ((the vaguest, most protean, and most treacher ous of psychological terms." Alexander Bain in his day discovered that it had already ac quired thirteen distinct meanings, and he would doubtless find additional ones were he con versant with the vastly increased psychological literature of the present time. Considering this lack of fixity in meaning it seems almost audacious to attempt an accurate definition. But, holding the term to its most important significance, one may define consciousness as the aggregate of the mental processes of any period of life.
The question of the relation of conscious ness to other biological functions is one of great importance but one upon which present scientific lcnowledge throws little light. There is every reason to believe that states and de grees of consciousness are directly correlated with the activities of the nervous system, and especially with the functions of the great master ganglion, the cerebrum. The evidence in ques
tion can be but briefly mentioned in this article. It is along two lines. First, comparative studies of the nervous systems of animals reveal the fact that their complexity increases pari passu with their level in the evolutionary series in other aspects of structure, and that with com plexity of nervous system goes increasing intelli gence in adjustive behavior. This is especially true of the cerebrum, the part of the nervous system that undergoes greatest elaboration as the animal scale is ascended, and also admits of the highest degree of organization under stress of the life experiences of each individual. Sec ond, experimental studies on the nervous sys tems of the lower animals, supported by patho logical evidence in the case of man, lead to the conclusion. that the several conscious processes are conditioned upon neural activity of a defi nite kind. Furthermore, functions have been accurately located in special cerebral areas, im pairment of which results in a decrease or cessation of the correlated form of conscious ness. Collateral evidence is also to be found in the facts of sleep and hypnosis. The cere brum during profound slumber has a lowered blood circulation, probably has a lessened rate of metabolism, and is analogous to an important part of a mechanism temporarily out of gear with the rest of the system. Likewise during sleep consciousness completely or partially dis appears. The hypnotic state gives indications pointing in the same direction, though lcnowl edge of the cerebral condition during hypnosis is so slight that one can speak only conjecturally The hypnotic subject appears to the observer to have an artificially delimited consciousness. His attention is acute within a narrowed field of stimulation. He is oblivious to all suggestion outside of this restricted range. When restored to normal condition there is usually a more or less complete forgetfulness of what took place under the hypnotic spell, analogous to the usual treacherous memory for dreams when recall is attempted some time after awaking from sleep. It is probable that there is a corresponding splitting off of cerebral activities into minor disconnected systems, some of them heightened into intense activity at the expense of others which become partially or completely somnolent.