Psychological self-examination (introspec tion) coincides with the verdict of common sense in distinguishing degrees of conscious ness. That such degrees are to be found in the ascending animal scale is the inevitable in ference from comparative studies of nervous mechanisms and of animal and human behavior. Evidence leading to the same conclusion comes from the scientific observation of a normal human being from earliest infancy to maturity. Further proof is found in the normal expen ences of sleep and waking as well as in the unusual ones of swooning and anmsthesia. The characteristic mark of consciousness at the lowest ebb is perceptual chaos and vaglieness. The signs of full consciousness are great clear ness and vividness. A high degree of con sciousness is hence practically identical with focalized attention, whereas a low measure of consciousness is similar to fleeting or scat tered attention. It would seem from this that consciousness and attention are terms with es sentially the same meaning.
Whereas older conceptions of consciousness regarded its contents as furnished entirely by sense-impressions, by intellectual intuitions, or by both together, more modern views have called attention to the contributions made by bodily movements. Recent views maintain that the stream of consciousness is a composite of external factors derived through sense and of other elements furnished by bodily move ments and activities. These movements give rise to so-called kinmsthetic (movement) sen sations. All perceptual judgments, for ex ample, arc conditioned upon strains and ten sions that blend with the other contribution of sense to construct the objects of our world. The content of consciousness is just these ob jects or things plus the residue of memory images, images of imagination and ideas which form the sum-total of conscious experience.
The last statement leads to a reiteration of the fact that consciousness always has content. The content includes all the mental acts by which life adjustments are carried on, such as sense-percepts, images, thoughts, acts of will and feelings. Consciousness is thus seen to embrace all the concrete elements of mental life. Its function would seem to be the biologi cal one of securing superior and far-reaching adjustments. It emerges at some unknown level in the animal scale in response to the necessities of living imposed by increasing com plexity of structure. It is sharply contrasted with the purely nervous mechanisms of reflex, impulse and instinct. The acquired mechanisms of habit are usually preceded by a conscious stage of learning in which there is a temporary guidance of ideation, but lapse completely into the non-conscious when perfected. So likewise of other psychic functions when the psychic shock of initial performance is dulled through inveterate use. From this fact it is manifest that consciousness is par excellence the organ of intelligent action. It is stocked with the percepts, images and concepts by means of which a more salutary contact with the world about us is secured.
A dosing word is required to speak of a very convenient antithesis to consciousness, the subconscious. Titchener defines it as "an extension of the conscious beyond the limits of observation? Beginner's Psychology,' p. 326). The concept has proved its usefulness in abnormal psychology, especially in the de partments of psychiatry and psychotherapy. The insane are often found to be dominated by complexes taking the form of dominant ideas and acting as urgent forces that over master self-control. Hysterical subjects exhibit similar compulsive psychoses of such power as to produce elaborate and persistent hallucina tions. Oftentimes there is no memory of the original experiences out of which these com plicated mental structures are pieced together by a diseased imagination. It is convenient to assume that the building up of these mental edifices of imagery takes place somewhere be hind the veil, much as the apparent dream imagery may be assumed to have been thrown into form behind the curtain of profound slum ber before it is marshalled into the presence of the hazy consciousness of the partially aroused dreamer. The investigations of such eminent psychopathologists as Freud and Jung tend to confirm the significance of the sub conscious as a convenient working hypothesis. It can scarcely be more; for direct evidence of its existence seems logically impossible.
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