Where would you place each of the following?

(a) Aphasia, where, through brain injury, the subject's vocabulary is very much reduced.

(b) The condition of the very old person, who cannot remember what has happened during the day, though he still remembers experiences of his youth.

(c) The "feeling of having been there before", in which you have a weird impression that what is happening now has happened in just the same way before, as if events were simply repeating themselves.

(d) The loss of memory which sometimes occurs after a physical or emotional shock, or after a fever, and which pa.s.ses away after a time.

3. How fully can you recall what happened on some interesting occasion when you were a child of 5-8 years? Dwell on the experience, and see whether you get back more than at first seemed possible. Try the same with an experience of five years ago.

4. If a student came to you for advice, complaining of poor memory, and said that though he put hours and hours on a lesson and read it over many times, still he failed on it, what questions would you ask regarding his method of study, and what suggestions would you offer?

5. An experiment on memorising lists of numbers. Prepare several lists of 20 digits, and shuffle them; draw out one and take your time for learning it to the point of perfect recitation. Write an introspective account of the process. Repeat with a second list

6. An experiment in memorizing word-pairs. Prepare 20 pairs of words as follows: take 20 cards or slips of paper, and write a different word on each. Then turn them over, shuffle, and write another word on the back of each. Thus, though you may know what words you have written, you do not how how they are paired; and now your job is to learn the pairs. Note starting time, take the first card and look at both {365} sides, and study the pair of words on this card for about 5 seconds, pa.s.sing then to the second card, and so on through the pack. Shuffle the pack, take the top card and give yourself about 5 seconds to recall the word on the reverse, then turning the card over and reading it. Proceed in this way through the pack, shuffle again, and repeat. Continue thus till you score 100 per cent. Note total time required, and report on process of memorizing.

7. Memorizing a series of related words. Prepare a list of 40 words, as follows: first write the numbers 1 to 40 in a column; then write any word for No. 1; for No. 2, write some word closely related to No. 1; for No. 3 some word closely related to No. 2; and so on. Your list, for example, might begin like this: house, roof, chimney, soot, fire, coal, mine, miner, strike, arbitration, etc.

Having finished writing your list, cover it and see how much of it you can recite without further study, and how long it takes you to complete the memorizing. Explain the results obtained.

8. Plot the curve of forgetting from the following data, which give the per cent, of retention of stanzas of a poem at different intervals after the end of memorizing.

after 1 day 79% after 2 days 67% after 6 days 42% after 14 days 30% after 30 days 24%

REFERENCES

Ebbinghaus, _On Memory_, 1885, translated by Ruger and Bussenius, 1918. This is the pioneer experimental study of memory, and is still worth reading, and is not specially hard reading.

James's chapter on Memory, in Vol. I of his _Principles of Psychology_, 1890, is still one of the best references, and contains some important remarks on the improvement of memory.

Of the numerous special studies on memory, mention may be made of that by Arthur I. Gates, _Recitation as a Factor in Memorizing_, 1917, which, on pp. 65-104, gives a valuable account of the various devices used by one who is memorizing.

For the psychology of testimony, see G. M. Whipple's article on "The Obtaining of Information: Psychology of Observation and Report", in the _Psychological Bulletin_ for 1918, Vol. 15, pp. 217-248, especially pp. 233-248. See also a popularly written account of the matter by Munsterberg, in _On the Witness Stand_, 1908, pp. 15-69.

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CHAPTER XV

a.s.sOCIATION AND MENTAL IMAGERY

SOMETHING ABOUT THINKING AS RELATED TO MEMORY

Memory plays a part, not only in "memory work", and not only in remembering particular past experiences, but in all sorts of thinking.

Recall furnishes the raw material for thought. A large share of any one's daily work, whether it be manual or mental, depends on the recall of previously learned reactions. Most of the time, though we are not exactly trying to remember facts committed to memory, we are recalling what we have previously learned, and utilizing the recalled material for our present purposes. For example, in conversation we recall words to express our meaning, and we recall the meanings of the words we hear. In adding a column of figures, we recall the sums of the numbers. In cooking a meal, we recall the ingredients of the dish we wish to prepare, and the location of the various materials and utensils required for our purpose. In planning a trip, we recall places and routes. Any sort of problem is solved by means of recalled facts put together in a new way. A writer in constructing a story puts together facts that he has previously noted, and any work of the imagination consists of materials recalled from past experience and now built into a new composition.

What Can Be Recalled

If recall is so important in thinking and acting, it is worth while to make a survey of the materials that recall {367} furnishes. In general, using the term "recall" rather broadly, we say that any previously learned reaction may be recalled. Writing _movements_ may be said to be recalled when we write, and speech movements when we speak. "Higher units", like the word habits and phrase habits of the telegrapher and typist, are in a broad sense recalled whenever they are used. The typist does not by any means recall the experience of learning a higher unit, but he calls into action again the response that he has learned to make. In the same way, the word habits and phrase habits of vocal speech are called into action, i.e., recalled, whenever we speak.

Besides these motor reactions, _tendencies_ to reaction can be recalled. The att.i.tude of hostility that may have become habitual in us towards a certain person, or towards a certain task, is called into activity at the mention of that person or task. The acquired interest in architecture that we may have formed by reading or travel is revived by the sight of an ambitious group of buildings. A slumbering purpose may be recalled into activity by some relevant stimulus.

Observed _facts_ can be recalled, and this is the typically human form of recall. In animals, we see the recall of tendencies and of learned movements, but no clear evidence of the recall of observed facts. To be recalled with certainty, a fact must have been definitely noted when it was before us. If we have definitely noted the color of a person's eyes, we are in a position to testify that his eyes are brown, for example; otherwise, we may say that we think probably his eyes are brown; because we have certainly noticed that he is dark, and the dark eyes fit best into this total impression.

We say that a fact is recalled when we think of it without its being present to the senses. While the original {368} observation of the fact was a response to a sensory stimulus, the recall of it is a response to some other stimulus, some "subst.i.tute stimulus". When John is before me, I observe that his eyes are brown in response to a visual stimulus; but I later recall this fact in response simply to the name "John", or in response to the question as to what is the color of John's eyes. I see what a square is by seeing squares and handling them, and later I get this idea simply in response to the word "square" in conversation or reading.

Memory Images

Now, can _sensations_ be recalled, can they be aroused except by their natural sensory stimuli? Can you recall the color blue, or the sound of a bugle, or the odor of camphor, or the feel of a lump of ice held in the hand? Almost every one will reply "Yes" to some at least of these questions. One may have a vivid picture of a scene before the "mind's eye", and another a realistic sound in the "mind's ear", and they may report that the recalled experience seems essentially the same as the original sensation. Therefore, sensory reactions are no exception to the rule of recall by a subst.i.tute stimulus.

A sensation or complex of sensations recalled by a subst.i.tute stimulus is called a "mental image" or a "memory image".

Individuals seem to differ in the vividness or realism of their memory images--the likeness of the image to an actual sensation--more than in any other respect. Galton, in taking a sort of census of mental imagery, asked many persons to call up the appearance of their breakfast table as they had sat down to it that morning, and to observe how lifelike the image was, how complete, how adequate in respect to color, how steady and lasting, and to compare {369} the image in these respects with the sensory experience aroused by the actual presence of the scene. Some individuals reported that the image was "in all respects the same as an original sensation", while others denied that they got anything at all in the way of recalled sensation, though they could perfectly well recall definite facts that they had observed regarding the breakfast table. The majority of people gave testimony intermediate between these extremes.

Individuals differ so much in this respect that they scarcely credit each other's testimony. Some who had practically zero imagery held that the "picture before the mind's eye" spoken of by the poets was a myth or mere figure of speech; while those who were accustomed to vivid images could not understand what the others could possibly mean by "remembering facts about the breakfast table without having any image of it", and were strongly tempted to accuse them of poor introspection, if not worse. It is true that in attempting to study images, we have to depend altogether on introspection, since no one can objectively observe another person's memory image, and therefore we are exposed to all the unreliability of the unchecked introspective method. But at the same time, when you cross-question an individual whose testimony regarding his imagery is very different from yours, you find him so consistent in his testimony and so sure he is right, that you are forced to conclude to a very real difference between him and yourself. You are forced to conclude that the power of recalling sensations varies from something like one hundred per cent, down to practically zero.

Individuals may also differ in the _kind_ of sensation that they can vividly recall. Some who are poor at recalling visual sensations do have vivid auditory images, and others who have little of either visual or auditory imagery call up {370} kinesthetic sensations without difficulty. When this was first discovered, a very pretty theory of "imagery types" was built upon it. Any individual, so it was held, belonged to one or another type: either he was a "visualist", thinking of everything as it appears to the eyes, or he was an "audile", thinking of everything according to its sound, or he was a "motor type", dealing wholly in kinesthetic imagery, or he might, in rare cases, belong to the olfactory or gustatory or tactile type.

[Ill.u.s.tration: Fig. 54.--Individual differences in mental imagery.

According to the type theory, every individual has a place in one or another of the distinct groups, visual, auditory, tactile, kinesthetic, or olfactory. According to the facts, the majority, of individuals cl.u.s.ter in the middle s.p.a.ce, and form a single large group, though some few are extremely visual, or auditory, etc., in their imagery. (Figure text: according to the type theory, according to the facts)]

But the progress of investigation showed, first, that a "mixed type"

must also be admitted, to provide for individuals who easily called up images of two or more different senses; and, later on, that the mixed type was the most common. In fact, it is now known to be very unusual for an individual to be confined to images of a single sense. Nearly every one gets visual images more easily and frequently than those of any other sense, but nearly every one has, from time to time, auditory, kinesthetic, tactile and olfactory images. So that the "mixed type" is the only real type, the extreme visualist or audile, etc., being exceptional and not typical.

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Limitations of Imagery

Recalled sensations are commonly inferior to their originals, both in the enjoyment they afford and in the use that can be made of them.

They are likely to be inferior in several respects.

(1) An image has usually less color, or tone--less body, realism and full sensory quality--than a sensation aroused by its appropriate peripheral stimulus. While you may be able to call up a fairly good image of your absent friend's face, the actual presence of your friend would be more satisfactory, just as a sensory experience. You may be able to run over a piece of music "in your head", and if your auditory imagery is strong you may even run over an orchestral piece, and get the tone quality of the various instruments; but, after all, such a mental concert is an imperfect subst.i.tute for a real orchestra. You enjoy a real whiff of the sea more than the best olfactory image you can summon. There is something lacking in these recalled sensations, and the trouble seems to be that they are not sensations enough; they lack sensory body.

(2) Images are apt to be sketchy and lacking in detail, and also narrow and lacking in background.

(3) Images are apt to be unsteady and fleeting, as compared with actual sensations. Where the peripheral stimulus, continuing, keeps the sensation going, the subst.i.tute stimulus that recalls a sensation is not so effective in this respect, any more than in giving body and detail. In all these respects, an image is less enjoyable and satisfying than an actual sensation.

(4) On the more practical side, images are inferior to the actual presence of an object, in that we cannot utilize the image as a source of new information. {372} We _cannot observe facts_ in the image of a thing that we have not observed in the actual presence of the thing.

At one of the universities, there is a beautiful library building, with a row of fine pillars across the front, and the students pa.s.s this building every day and enjoy looking at it. It has long been a favorite experiment in the psychology cla.s.ses at that university to have the students call up an image of the library, and to have them state how clear their image is, how complete and how vivid. Then they are asked to count the pillars from their image, and to tell what kind of capitals the pillars have, and whether the shafts are plain or fluted. But at this point the students begin to object. "We have never counted those pillars, and cannot be expected to know the number now."

In fact, few of them give the correct number, and those who have reported clear and vivid images are little better off in this respect than those whose images are dim and vague.

The image, then, does not give you facts that you did not observe in the presence of the object. The subst.i.tute stimulus, which now recalls the image, only recalls responses which you made when the real object was the stimulus. If you looked at the object simply to get its general appearance, the general appearance is all you can recall. If you noted the color of the object, you can probably recall the color.

If you noted such details as the number of pillars, you can recall these details. But the subst.i.tute stimulus that now arouses the image is by no means the equivalent of the original peripheral stimulus in making possible a variety of new reactions. Its only linkage is with reactions actually made by you in response to the real object. The subst.i.tute stimulus, such as the name of a building, became linked with responses actually made by you, not with responses that you simply might have made, when the object was present. This important fact is closely related to the {373} unreliability of testimony that was mentioned before under the head of "unintentional memory".