Sensory memory has long been subdivided by psychol- ogists into several "types", chief among which are the auditory, visual, and motor. Anyone may re- member at times by visual, auditory or other sensory images; but the prevailuig character of his imagery determines his memoiy type. To some extent tlie type depends on training; out 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 f iir die Ges. Psychol.", 1905, IV, 367-8).
Besides sensory and intellectual memory, a third division, affective memory, is often mentioned. Meu- mann (Vorlesungen zur Einfiirhung in die experi- mentelle Piidagogik, 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 Lol:>sien. 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 Psychologic des sentiments, 166). Titchener ("Affective Memory" in "Philos. Review", IV, 1S95), objected to the type theory of affective memory, on the ground that affec- tions, unlike mental images, are recalled in company with ideational mental processes. They are not in- dependent 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 inde- pendent 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 op 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 mem- ory have been distinguished: (1) 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 unfavourable 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: (1) external objects, (2) words of visual con- tent, (3) words of auditory content, (4) tones, (5) touch and sensations of movement, (6) numbers and abstract ideas, (7) emotions (cf. Meumann, "Vorle- sungen zur Einfiihrung in die experimentelle Pada- gogik", 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, mem- ory 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 al- most constant. By analogy with the general biologi- cal 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 sugges- tions 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 mem- orize any kind of connected narrative, we are greatly helped if we first analyse its logical secjuence of thought. Memory systems for translating dates into words and memorizing the words which can be re-translated 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 ilown 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 favour of the first method, it is the one that consiunes 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 rea- son 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. Conse- quently 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, " Ex- perimentelle 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 en- tirely to oneself. In memorizing poetry, it should be read with the rhyt.hmic swing of the metre. 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 remem- ber 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 Me.mory. — .^s a psychological process, memory includes three elements: (1) retention, (2) reproduction, (3) recognition. The process of recog- nition is usually treated more or less as a separate problem, so that the discussion of the theory of mem- ory has centred around the question, how it is possible for ideas to be retained and reproduced. What be- comes 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. It 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