The mental mechanisms by which the un conscious pervades and indirectly controls all the conscious expressions, whether activities or thoughts, will be discussed under the title PSYCHOANALYSIS. In connection with mem ory it is necessary here only to point out that what we remember is only the residua after the work accomplished by the processes of repression, during which most of our former experiences are forgotten. On the fundamental principle that what is unpleast ant in experience is from earliest infancy rejected by the individual ego, and regarded as if it did not exist, we may regard the ego as similarly rejecting or repressing the memories of impressions associated with the unpleasant or painful incidents. This explains why some things are forgotten and others are remembered. The unconscious, which functions solely on the principle of accepting or striving for the pleasurable and rejecting or repressing the painful, theirfore lurid es the motive force for injecting certain id( t into conscious ness, and restraining other id' ; from entering. On this fact depends the iurtner phenomenon that the dynamic factor called the libido, in be coming attached to certain ideas which are thrust out of consciousness, may be converted and its force applied to vegetative functions of the body producing in many cases certain forms of disease. See PSYCHOTHERAPY.
Memory, however, does not depend on repeti tion of stimulus alone. There are variations in intensity and duration of stimuli, modifications in plasticity of the nerve-cells themselves, the quality of attention, and above all the native in dividual character of health of the nerve-tissue itself—all of which factors enter into the every day variations in memory that are familiar to all. The fixity and enduring quality of the memories of childhood are proverbial, and are due to the great plasticity of the youthful nerve cells, as well as to the intensity of the early pictures. That one person should have a good visual memory and a poor auditory memory, and vice-versa, must naturally he interpreted as due to variations in individual capacity. Modern pedagogy has slowly recognized these variations, and the greater prominence given to play, and to methods of precition, , they manual, lingual, auditoria' or visual, and less to distinctly formal methods • of memorising • as a purely visual process from a printed page, may be regarded as evidence of •this wider recogni tion that memory should be a generalized tune. don, and not a 'pedantic cramming of any sort, A well-trained muscular system may be of far greater use to 'a man than any of his acquired knowledge. It is impossible to train certain children to do certain things, whereas in other directions •training may result in great proficiency.
Disorders of The classifications of disorders of memory into those of defect and those of excess• is based on the old psychol ogy which laid most of the defects to lesions in the cortex of the brain. The newer view, while admitting the ,loss of memory evinced by the physical defect in the brain or nerve substance, admits, also a purely functional deficiency in various memories which is determined by the unconscious wish and is entirely independent of any organic lesion or defect. It is agreed by
Most psychologists that the native retentiveness in any given individual does not itself alter, although there may be in one individual a finer nerve and brain structure than in another, enabling one to perceive and therefore retain finer distinctions. But the ability to recall at will, which is the essential quality of a good memory in the ordinary sense, is dependent solely upon the proper alignment of the tin, conscious wish with the desires of the conscious life, ,which are determined by the Social en vironment of the individual.
The general term for deficiency or loss of memory is amnesia, although this term fails to express the various distortions of memory, the illusions or slight absences; and there are no technical words to distinguish temporary or permanent, periodic or progressive stages of the amnesic process. Inasmuch as memory is not one thing, but a great assemblage of processes which reflect a vast variety of psychological functions, situated not in the brain alone, but almost anywhere in the nervous system, a feet in memory," as defined by Jastrow, is an expression of the incapacity of a group (or of certain groups) of centres to exercise their normal functions; or a tendency which they show • to functionate in an abnormal manner.' Defects of memory may be general or special. General defects may be due to an incapacity on the part of nervous centres to establish residua. This type is found in those people who never remember what they see, and, not withstanding frequent repetition of an ace, never acquire proficiency in it. Occasionally a reverse general condition is manifest wherein the power of memory is unduly exalted and im pressions of past experience reappear with un usual brilliancy. Such states are known in fevers, in intoxications of various kinds as of alcohol, opium, etc., and in the hypnotic trance. Special defects may arise in which particular iso lated experiences are cut out of the mind. Thus alcoholic amnesia. that may forget even a com mitted crime, is an illustration. Somnambul ism and other hysterical states are characterized by defects of this special type. Another form of defect is observed when associated memory groups are blotted out, as in the special dis Order aphasia. (See APHASIA; SPEECH, DEr FECTS or). Memory may be falsely localized in time, or in order; imaginary additions to - _ real events may be present; or illusory remem brances of what has never been experienced occur. Disorders of memory are never primary conditions but depend upon either the physical nerve or brain defect for which there must al ways be a corresponding deficiency in memory or upon the psychological conditions referred to above, where the specific memories are in hibited by associations with unpleasant or pain ful situations. Through the technique of psychoanalysis a great amount of forgotten material can be restored to memory by means of living over again the situations in which occurred the events responsible for the ap parent obliteration of the memory.