Capability of the mind, to store up conscious processes, and reproduce them later with some degree of fidelity
Memory (Lat., memoria), is the capability of the mind, to store up conscious processes, and reproduce them later with some degree of fidelity. Strictly speaking, however, a revived conscious process is not remembered, unless it is, at the same time, recognized as something which occurred before. Memory, therefore, involves a process of recognition. Voluntary reproduction of mental processes is frequently spoken of as recollection, and involuntary, as recall.
DIVISIONS OF MEMORY.—St. Thomas distinguishes two kinds of memory, sensory and intellectual. He excludes, however, from the former the function of merely storing up the mental image; this he assigns to imagination. Sensory memory preserves that which can not be received by the special senses and yet is individual, and therefore does not belong to the intellectual memory, which takes cognizance of nothing but the universal. For instance, the utility of an object and its setting in past time; by the utility of an object must not be understood any abstract concept of its purpose, but only the sensory experience which all animals acquire, that certain things are beneficial or harmful. Sensory memory is located by St. Thomas in the bodily organism (I, lxxviii, a. 4). The intellectual memory receives and stores up the abstract and universal. Its seat is the passive intellect, a division, or perhaps only an aspect of the faculty of understanding. The complement of the passive intellect is the intellectus agens, which is conceived of as actively working over the data of sense, abstracting from them the universal (species intelligibilis) which they contain and impressing it on the passive intellect. St. Thomas argues that there must be an intellectual memory, because that which is acted upon must retain the effect of the agent all the more perfectly in proportion to its own stability. Since the impressions of sense leave lasting traces on the bodily organism, which is subject to decay,—a fortiori the universal must, in some way, be stored up in the passive intellect, which is a spiritual faculty, permanent as the soul itself (I, Q., lxxix, a, 6-7).
This argument assumes that there are cognitive processes specifically different from those of sensation, a doctrine which has received scant recognition in modern psychology until quite recently. The tacit or expressed assumption of many experimental psychologists has been the very opposite, viz.: that all our cognitive processes are sensations or sensory complexes. Recently, however, the attempt has been made to demonstrate experimentally the existence of abstract thought, totally distinct from mental imagery (phantasms). Along with this admission of a difference between sensation and thought, experimental psychology is beginning to emphasize the distinction between sensory and intellectual memory. Sensory memory has long been subdivided by psychologists into several "types", chief among which are the auditory, visual, and motor. Anyone may remember at times by visual, auditory or other sensory images; but the prevailing character of his imagery determines his memory type. To some extent the type depends on training; but there is evidence to show that it is in part determined by anatomical or physiological conditions of the brain. This, however, does not exclude the modification of images by any exercise of memory in which they function; for the type is quite elastic (Watt, "Experimentelle Beitrage zu einer Theorie des Denkens" in "Archiv fur die Ges. Psychol.", 1905, IV, 367-8).
Besides sensory and intellectual memory, a third division, affective memory, is often mentioned. Meumann (Vorlesungen zur Einfürhung in die experimentelle Padagogik, I, 174) recognizes it as a distinct form, because in children under thirteen, it is but little developed; whereas other forms of memory are already far advanced. Meumann's view is based on the experiments of Netschajeff and Lobsien. Ribot, who was the first to make a special study of affective memory, maintained that to the visual, auditory, and motor types, we must add another, which is just as well defined, i.e. the affective type (La Psychologie des sentiments, 166). Titchener ("Affective Memory" in "Philos. Review", IV, 1895), objected to the type theory of affective memory, on the ground that affections, unlike mental images, are recalled in company with ideational mental processes. They are not independent but dependent mental processes, and can only be attended to, or recalled in company with the representative processes, of which they are but qualities or tones. Conclusive evidence is at present lacking, to decide whether or not feelings are dependent or independent processes. But the settlement of this problem is not necessary for the recognition of an affective memory of some kind. The expression "affective memory" is justified because affective processes are distinct from sensory and intellectual.
THE DEVELOPMENT OF MEMORY.—The growth of memory from childhood to maturity is dependent upon the development of many mental faculties, and is therefore a very complex affair. It is a growth of many memories, rather than of a single faculty. For purposes of experiment, the following forms of memory have been distinguished: (I) memory for special sensations, (2) for impressions of space and time, (3) for things and events of the outside world, (4) for numbers and abstract concepts, (5) for emotional states of mind. Each shows a period of rapid growth, followed by a standstill or even a retardation. The fourteenth and fifteenth year of childhood is especially unfavorable for the development of all kinds of memory. The order in which these forms of memory undergo their period of rapid development, is, for boys: (I) external objects, (2) words of visual content, (3) words of auditory content, (4) tones, (5) touch and sensations of movement, (6) numbers and abstract ideas, (7) emotions (cf. Meumann, "Vorlesungen zur Einfuhrung in die experimentelle Padagogik", I, 178). It is not true that the memory of children is better than that of adults. Except for a retardation at the ages of fourteen and fifteen, memory grows continuously, reaching a maximum between twenty and twenty-five. After that, for those in learned pursuits, it declines very slowly, until about the fiftieth year, when it commences to fall off more rapidly. Ebbinghaus, who made continual tests of his powers of retention, could say at the age of fifty-two, that for twenty years his memory remained almost constant. By analogy with the general biological law of exercise, Meumann concludes that memory fails more slowly the more frequently it is used.
THE METHOD OF MEMORIZING.—The experimental study of memory has not been barren in results of practical value. It is now possible to give suggestions for the practical work of memorizing that are based upon very definite data. These suggestions refer primarily to the mechanical part of memory. Practical experience tells us that if we want to memorize any kind of connected narrative, we are greatly helped if we first analyse its logical sequence of thought. Memory systems for translating dates into words and memorizing the words which can be retranslated into dates, are so cumbersome that their value is doubtful. The results of experimental work aid us chiefly in the drudgery of memorizing—just where conjecture about the best method is most likely to fail. In learning a a poem by heart, the usual method would be to read the first few lines several times, then read from the beginning on down a few lines further and so, little by little, commit the whole to memory. Another method would be to read it each time, from beginning to end, until it was perfectly memorized. Although there is a prejudice in favor of the first method, it is the one that consumes the greatest amount of time.
Several pieces of experimental work have shown that memorizing by reading from beginning to end, is the quicker and more permanent method. The reason is to be sought in the mechanics of association, by which one part of the piece memorized is bound to the other. When a series of words is memorized, it may be shown that a word is not merely associated with the one that precedes and the one that follows it, but also with every other word of the series. Consequently the "total" method, avoids the trouble of connecting the separate sections of the partial method, makes the bonds between the divisions more secure, and gives to all the parts a certain equality of value by which the whole is better united. (Steffens, "Experimentelle Beitrage, etc." Ch. iii.) One will, of course, combine at times the two methods. When certain portions of a piece present special difficulties, these parts will be more deeply impressed by a few special readings. It has also been found that, in memorizing, it is better to read half aloud than entirely to oneself. In memorizing poetry, it should be read with the rhythmic swing of the meter. As to the rate of reading, it has been found that, if one wants to learn a piece so as to be able to repeat it, as soon as he has memorized it, he will save time by reading rapidly. But he will forget it more quickly than if he reads leisurely. Since one generally wants to remember what he has learned for some hours at least, it is better to read through the material at a leisurely rate. Meumann recommends that in the first part of the memorizing, one should read slowly, and more rapidly later on, as the material becomes familiar.
THEORY OF MEMORY.—AS a psychological process, memory includes three elements: (I) retention, (2) reproduction, (3) recognition. The process of recognition is usually treated more or less as a separate problem, so that the discussion of the theory of memory has centered around the question, how it is possible for ideas to be retained and reproduced. What becomes of the idea after it leaves the present state of consciousness? Does it continue to exist, preserving its own peculiar being, somewhere in the depths of the mind, and reappear when the occasion is propitious? Such was the opinion of the German philosopher and pedagogue Herbart (1776-1841). This would only be possible, if the idea were a substantial being, which rose up from the depths of consciousness whenever the mind became aware of it, disappearing when it was forgotten—a theory more picturesque than true. If the idea is not a substantial entity, it must be a kind of accident—a transient something that continues to exist only in the traces that it leaves in passing. This is the common theory of memory, which takes on many forms, according as the "trace" is located and explained. Descartes located the trace primarily in the bodily organism. In remembering, the soul has to drive the "animal spirits" hither and thither in the brain, till they encounter the trace of the idea it wishes to recall. But, besides the cerebral traces, there are also, according to Descartes, vestiges left in thought itself. Leibnitz located the trace in the monad of the soul and conceived of it as becoming vanishingly small, but never equal to zero. For others again, the trace is entirely material. Some even go so far as to locate each image in a special ganglion cell of the cortex. On account of its definite character and picturesqueness, this theory has found many popular expositions. But there are facts that seem to make it untenable. For instance, disturbances of vision caused by unilateral lesion in one visual area of the cortex of a dog, wear off after about six weeks. This was explained by supposing that new memory images are deposited in the surrounding area. But it was shown by Loeb, that when dogs are kept in complete darkness after the operation (so that the acquisition of new visual images would be impossible), on being released after a period of six weeks, they are, nevertheless, entirely normal (Loeb, op. cit. infra, xvii).
More recently, it has been maintained (Robertson, "Sur la dynamique du Systeme nerveux etc.", 438), that the trace is a chemical condition left in the brain by the passing activity of the original impression. This contention is not pure speculation, but is based upon experiments which aim to show that sensory processes are connected with the liberation of acids in the cerebral tissues. This leads to the assumption that "the extent of the memory-trace is proportional to the amount of material transformed in a self-catalysed chemical reaction, that the number of syllables memorized must be connected with the number of repetitions (or time of learning) according to the following function: Log. n=Kr +b; where n is the number of syllables memorized, r is the number of repetitions, and k and b are constants (that is, do not vary when n and r vary)" ("Monist", 1909, XIX, 383). The quantity n also corresponds to the amount of substance transformed in the chemical reaction, and r to the time during which it goes on. Calculations based on this equation, compared with observed results, gave very small percentages of error: 0-46 per cent. to 2-5 per cent. Such results seem to indicate that the term "sensory trace" will eventually receive a definite explanation, but they are far from affording us the basis of a complete explanation of memory. The insufficiency lies in the fundamental defect of all materialistic theories. They fall short of that which they start out to explain: the conscious processes of memory. It is not sufficient to show that there are cerebral traces. This has long been a priori evident, and it is to be supposed that such traces will obey a definite law. Over and above this, a complete theory of memory must show how these cerebral traces recall definite conscious processes. This problem remains unsolved. In our haste to find some solution we must neither deny, with the materialist, the first facts known to us, our conscious processes, nor with the idealist refuse to allow one of the primary deductions from these facts, an external something that gives rise to our sensations. Scholastic philosophy has always recognized the fact of man's dual nature—a fact which must be taken account of in any theory of memory. St. Thomas postulated the existence of physiological traces in the organism. But he also pointed out that there must be some kind of residue of the ideas left in the soul itself. Since the ideas are but acts of intelligence, and not intelligent substances—transient activities of the soul itself—and not complete beings on which the mind turns its gaze, they can only live on, as dynamic traces in the passive intellect, awaiting the time when they will exert their influence on some future process of thought—apparently rising from the depths of consciousness, in the act of memory.
The function of memory is further significant as evidence for the substantial nature of the soul. Since ideas are transient processes, there must be a permanent something in the mind to account for their retention and reappearance; and since they are recognized as ideas that were formerly in consciousness there must be something that identifies them and that consequently persists during their absence from consciousness (see Soul.). The attempt to explain retention by means of psychical dispositions distinct from cerebral traces, is obviously futile unless it postulates a substance of mind in which such dispositions are preserved.
THOMAS V. MOORE