rapidly the first hour, proportionately less for the next seven hours, and still more slowly through the balance of the first twenty-four hours. "After a whole month fully one-fifth of the first work persisted in effect." Toward the latter part of the month the loss seemed so slight that Ebbinghaus was led "to predict that a complete vanishing of the effect of the first memorization of these series" [of nonsense-syllables] "would, if they had been left to themselves, have occurred only after an indefinitely long period of time." There is no essential difference between the findings of Ebbinghaus and later investigations. The chief disagreement is concerned with the rapidity of forgetting, immediately and soon after committing a selection to memory. Ebbinghaus' curve of forgetting appears to fall too rapidly at the outset.

Most of the tests of forgetting have been made on children or adults who learned either nonsense-syllables or selections with meaning just well enough to repeat them once without error. In the course of the investigations, however, the ability to recall was found to depend, among other things, upon the number of repetitions, upon the distribution of periods of work, and upon the number and nature of the associations formed. We accordingly turn to these memory-aids.

Repetition fixes memory. Experience shows this. If we wish to remember a name we repeat it. Investigation1 of the effect of a number of repetitions have not only justified this conclusion from experience, but they have also contributed several other significant facts.

First of all, during the repetitions the mind should be

1 A. Binet et V. Henri, op. cit. Hermann Ebbinghaus, Memory, pp. 52 ff.; Grundzüge der Psychologie, third edition, vol. 1, pp. 652 ff. P. Ephrussi, op. cit. E. A. Kirkpatrick and Abbie F. Munn, Archives of Psychology, no. 12, p. 36. Otto Lipmann, Zeitschrift f. Psychologie, vol. 35, p. 195. Max Offner, Das Gedächtnis, Berlin, 1909, pp. 47 ff. Adclf Pohlmann, op. cit., pp. 65 ff. Fritz Reuther, Wundt's Psychologische Studien, vol. 1, p. 4. W. G. Smith, Psychological Review, vol. 3, p. 21. F. Weber, Zeitschrift f. experimentelle Pädagogik, vol. 8, p. 1.

actively attentive. It has been found that a combination of reading and repeating gives the best results for memory. Repeating aloud requires more effort and concentrates the attention better than silent reading. The latter is more likely to be passive. Experiments have shown, also, that memory is more than 50 per cent better if the learner is informed that the effect of the repetition will be tested than when he assumes that there will be no test.

Then, again, all repetitions are not of equal value in fixing impressions and ideas. To be sure, Ebbinghaus found that fewer repetitions were required to relearn a series of nonsense-syllables after twenty-four hours when the original number of repetitions was greater. And this saving was proportional, in a general way, to the added repetitions during the first learning, provided they did not exceed a certain number, not very accurately defined. More careful measurement of the relative efficiency of successive repetitions, however, has proved that the earlier repetitions have the greatest fixing power. This seems to be specially true in immediate memory-memory tested as soon as the learning is completed. Again, when the repetitions greatly exceed the number necessary for the first correct reproduction their efficiency gradually lessens until the gain becomes hardly measurable. Finally, it was observed that the value of repetitions varied with their distribution. This is of special importance not merely for students but also for those in the larger outside world of business and professional life. One or two questions will clear the ground.

Is it better to commit a selection of prose or poetry to memory at a single sitting, or is it advantageous to distribute our efforts over several days? Which plan brings the desired result with the least expenditure of energy? Quite a number of investigations have been made and

1J. Larguire des Bancels, L'Année psychologique, vol. 8, p. 185. C. H. Bean, op. cit. M. Browning, D. E. Brown, and M. F. Washburn, American

there is general agreement that a distribution of periods of study gives the best results.

Ebbinghaus found, in committing nonsense-syllables to memory, that thirty-eight repetitions distributed over three days produced the same results as sixty-eight repetitions at a single sitting. Starch experimented with fortytwo students. They were divided into four groups, one of which worked ten minutes at a time twice a day for six days; the second group twenty minutes at a time once a day for six days; the third worked forty minutes every other day for six days; the fourth did the entire task at one sitting of two hours. The results showed a great advantage for the shorter, more widely distributed periods. The two-hour period of work at one sitting was a bad fourth. The advantageous periods of work in this experiment seem short, but the occupation consisted in associating numbers with letters, a task which would quickly cause fatigue.

Jost carried these experiments much further than any of the other investigators and proved that neither fatigue nor inattention explains the advantage of this distribution of time. Having eliminated these two factors, he undertook to determine the best arrangement of periods of work, and he found that twenty-four repetitions, distributed over twelve days with two repetitions a day, gave better results than less distributed periods. He inclines to an even more extended distribution. If we accept Jost's view, that the

Journal of Psychology, vol. 24, p. 580. Hermann Ebbinghaus, Memory, p. 89; Grundzüge der Psychologie, third edition, vol. 1, pp. 657 ff. John Bigham, Psychological Review, vol. 1, p. 453. Alfred Binet, L'Année psychologique, vol. 10, p. 116. W. F. Dearborn, Journal of Educational Psychology, vol. 1, p. 273. Adolf Jost, Zeitschrift f. Psychologie, vol. 14, p. 436. E. A. Kirkpatrick and Abbie F. Munn, op. cit. J. H. Leuba and Winnefred Hyde, Psychological Review, vol. 12, p. 351. O. Lipmann, op. cit. E. Meumann, Psychology of Learning, pp. 265 f. G. E. Müller and A. Pilzecker, op. cit. Max Offner, op. cit. Nellie L. Perkins, British Journal of Psychology, vol. 7, p. 253. Adolf Pohlmann, op. cit., pp. 82 f. Fritz Reuther, op. cit. D. Starch, op. cit.

advantage of distributed practice and study1 lies in the greater effectiveness of old associates, Miss Perkins' results2 "indicate that this process of consolidation continues for at least forty-eight hours, and still longer if four or more readings are made on each day" [of practice]. Putting these investigations into general terms, the experiments show conclusively that an extensive distribution of study periods for a given piece of work is advantageous both for rapidity of learning and for permanent retention. The period favorable for one sitting and the length of intervening time will depend, among other things, upon the nature of the material and the difficulty of the task, with its accompanying fatigue. The economy of distributed study, instead of finishing what one is engaged upon and then dropping it, may then be considered established.

Jost next sought to determine why it is more advantageous to spread study or practice over several days instead of finishing the work at one sitting. He came to the conclusion that older associations-those which were established earlier—are more easily renewed than the more recent ones. This explanation, however, still leaves the question Why? unanswered. Some find the explanation in the effect of activity upon the nutrition of the organ exercised, and in the dropping out of interfering associations. This would be a satisfactory explanation were considerable practice always involved. But the same advantage of distributed study is observed when the selection is read but once each time. A "setting" or "fixing" of associations, on the other hand, apparently satisfies conditions. Those that are older have had more time in which to become "fixed." Since it is difficult to understand in what this "fixing" consists, unless it be the result of cere

1 Jost experimented only upon learning and relearning, i. e., memory. 2 Op. cit.

3 Physiological Psychology, by G. T. Ladd and R. S. Woodworth, p. 581.

bral nervous activity, we seem at present compelled to take this view.

This explanation of the "setting" of associations during periods of rest is also indicated by experiments in relearning skilful acts after a long interval without practice. The writer at one time acquired considerable proficiency in tossing two balls with one hand, one ball being caught and thrown while the other was in the air. More than six years later he again tested himself in this feat. In eleven days he greatly exceeded the skill which he had acquired six years before after forty-two days of arduous practice. The following curves show the progress during the original learning process, and during the test in relearning the same feat six years or more later. The curve of relearning is on the left. The rate of progress is shown at the left of the perpendiculars, and the days required in each case are indicated under the base line.1 The practice in which the skill was first gained was finished six years before this memory test was made. After the conclusion of the first investigation there were five monthly tests of the effect of intermission of practice, and one memory test two years later. With these exceptions there had been no practice during the six years.

The writer has also determined the effect of intermission of practice on the typewriter.2 In this instance, the memory test was made more than two years after the close of the first experiments by which a certain degree of skill was attained. During the intervening two years he had not used any style of typewriter. The original investigation covered a period of fifty days, while in the memory test, two years later, only eleven days were required to reach the degree of proficiency with which the original investigation closed.

This curve is reproduced from the Psychological Bulletin, vol. 7, 2 Psychological Bulletin, vol. 3, p. 185,

p. 17.