The Encyclopedia Americana (1920)/Memory and its Disorders
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Memory and its Disorders
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MEMORY AND ITS DISORDERS. Locke has defined memory as “the power the mind has to revive perceptions which it once had, with the additional perception that it has had them before.” Ribot distinguishes three functions of memory: (1) the preservation of certain states, (2) their reproduction and (3) their recognition. In view of the fact that the collection of gray matter in the cerebro-spinal axis below the cortex is capable of storing impressions and that probably all parts of the sensory nervous system are concerned in mind action and in memory, it will be necessary to speak not merely of memory but of memories, in the sense of reproductions of like sense quality with the original impressions. Modern psychology accepts the concept of unconscious memory, which would imply that all impressions upon all sense organs are permanently retained in the organism. In this case the question is not so much how we remember as why we forget. An answer to this question has been found by the present day analytical psychology of the unconscious. Up to the time of the acceptance of these views the determinants of memory were considered to be frequency of repetition of the stimulus, or its intensity, or its interest or a combination of these factors. From a purely mechanical point of view memory is interpretable as a result of a biochemical phenomenon. The sensory nerve cells, being acted on by certain stimuli, whether of touch, taste, hearing or sight, undergo certain molecular changes. Repetition of similar impulses induces similar reactions and a habitual response in the affected cells results. A line of least resistance is established and in these habitual responses the germ of the idea of memory is to be found.
From this point of view the nerve-cells retain something as a result of a previous experience, and the repetition of the stimulus finds the cells in a receptive state. Continued repetition of the stimuli constitutes a memory, and in this sense the training of a certain mechanism has bound up in it this mechanical theory of memory. Thus a muscular effort, as in tennis, or skating, or piano-playing, becomes by repetition remembered in automatic action, frequently without consciousness. It is the usual rule that many muscular acts which in their acquisition have called for conscious memories soon become automatic, and the effort no longer rises into consciousness, perhaps because of its diminished intensity. A similar point of view may be held for sound-impressions, for taste, for touch; for sight, in each individual case a different series of nerve-cells and nerve-fibres being involved. Thus the memory for a poem may mean a habit-response to a series of sight or sound impressions, or of the muscular memories of the speech mechanism that has learned to repeat the phrases. The actor who mechanically plays, or the golfer who unconsciously drives true, all show the same class of memory adaptations, involving different nervous chains.
There are thus not only a visual memory, but an auditory memory, or memory for sounds, a gustatory memory for tastes, an olfactory for smells, and special memories for the other special classes of sensation. Older psychology was concerned with the question as to the fidelity and longevity of these special memories or types of memory, as related to each other, and with the discovery of laws according to which they might be revived. (See Mnemonics). But with the introduction of the unconscious as a dynamic factor, the recalling of a previous experience is explained on a new principle. Memories are thus seen in the form of ideas to be reproduced into consciousness by virtue of forces which are mainly unconscious, and over which consciousness has only an indirect control, and the study of memory as such retires to an importance secondary to the study of the causes why some things tend to be remembered and others tend to be forgotten. This trend or tendency on the one hand to be forgotten or on the other to be remembered is now known to be determined by the unconscious wish, a force which is termed the libido and which is the prime mover, although uniformly unrecognized, of all the activities of the ego, both conscious and unconscious.
The mental mechanisms by which the unconscious pervades and indirectly controls all the conscious expressions, whether activities or thoughts, will be discussed under the title Psychoanalysis. In connection with memory 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 unpleasant 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, therefore furnishes the motive force for injecting certain ideas into consciousness, and restraining other ideas from entering. On this fact depends the further phenomenon that the dynamic factor called the libido, in becoming 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 repetition 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 individual character of health of the nerve-tissue itself — all of which factors enter into the everyday 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 be 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 precision, be they manual, lingual, auditorial or visual, and less to distinctly formal methods of memorizing as a purely visual process from a printed page, may be regarded as evidence of this wider recognition that memory should be a generalized function, 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 Memory.— The classifications of disorders of memory into those of defect and those of excess is based on the old psychology 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 unconscious wish with the desires of the conscious life, which are determined by the social environment 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 “defect 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, notwithstanding frequent repetition of an act, never acquire proficiency in it. Occasionally a perverse general condition is manifest wherein the power of memory is unduly exalted and impressions of past experience reappear with unusual 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 isolated experiences are cut out of the mind. Thus alcoholic amnesia, that may forget even a committed crime, is an illustration. Somnambulism 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 disorder aphasia. (See Aphasia; Speech, Defects of). Memory may be falsely localized in time or in order; imaginary additions to real events may be present; or illusory remembrances 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 always be a corresponding deficiency in memory or upon the psychological conditions referred to above, where the specific memories are inhibited by associations with unpleasant or painful situations. Through the technique of psychoanalysts 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 apparent obliteration of the memory.
Psychologically considered, memory defects nay occur either in the storing or retentive part of the nerve-cells, or they may involve the much more complicated and associated process of reproduction of the retained images. Both processes may be involved at the same time. In imbecility, idiocy, dementia, etc., a born of acquired loss of retentive power is present. In pianists — for example, Paderewski — or chess-players — Morphy, Pillsbury, etc., a state of localized hyperamnesia is present. This group would include all such prodigies. Occasionally one sees these two groups represented in one individual, as in an imbecile who has great power for mathematical calculation, etc. A case of this kind proves that the old assumption of closely localized memory-centres is false. Memory may be said to reside in all parts of the sensory nervous system. In another group the ordinary amnesias may be placed. These vary with each individual and depend largely on the healthy tone of the nervous system. A third group would include the paramnesias, or illusions of memory. In this condition (1) there is a loss of distinction between memory of things which really did happen and an imagination of things which never did or could. The so-called “constitutional liar” is an example of this inability to distinguish between real and imaginary, and many types of insane persons are similarly affected in an extreme degree. The reverse of taking an imagination for a real thing is (2) taking a real thing experienced for the first time as a memory of something experienced before — thought of having seen, heard or felt “just that same thing before,” also called “deja vue.” Such a feeling has nothing to do with native retentiveness, but only with the “feeling of familiarity,” which is essentially the presence of an organic sensation which is absent in the simple paramnesia. In some insanities this form of double memory is very prominent and leads to the belief on the part of the person so affected that he is prophesying when he is only recalling what he experienced before. (3) There is also an associated paramnesia in which things actually experienced suggest ideas falsely taken as memories of other things never experienced. This condition is seen in children and often leads to false testimony. It is also responsible for most “presentiments” or alleged antecedent knowledge of what has happened. Examples of such memories of the actually non-existent are seen in the stories of faith cures, where all the healing is that of ills that never really existed, save as associated false memories. On these false memories is erected much of the complicated structure of spiritualism, second sight and other similar phenomena. See Idiocy; Personality and Its Disorders; Speech, Defects of; and Retentiveness.
Bibliography.— Baldwin, ‘Dictionary of Psychology and Philosophy’; Freud, ‘Psychopathology of Every Day Life’ (chapter in ‘Forgetting,’ 1917); Ribot, ‘Diseases of Memory’; Guillon, ‘Les Maladies de la Mémoires,’ with full consideration of hyperamnesia (1897); Sallier, ‘Troubles de la Mémoire’ (1892), and Pardo, ‘I disturbi della memoria’ (1899).