The interval between learning and repetition is much more important than people usually assume, and it is one of the factors regrettably neglected in our school education. Almost every good book on psychology and learning stresses the importance of these intervals, but I have not yet seen a single school-book that takes advantage of these findings.
Ebbinghaus, a German professor, devoted much time to experiments in this particular line, and his tests have been checked and double-checked in almost every country.
You know as well as I do that it is entirely wrong to assume that any subject-matter which we once learned and mastered will remain our mental property for ever. You know that a person may have spoken a foreign language rather fluently but, by not using it for several years, may have lost the ability to completely and be forced to admit that he can neither speak it nor understand it any more.
Of course, that cannot happen if he uses the language constantly. Use is repetition, and repetition is necessary for everything which we wish to keep alive in our minds. So far, the facts are known to everyone. What is not so well known is that the spacing of repetition plays a very important role in time-saving.
Ebbinghaus has found that a subject which requires 68 repetitions if learned in one day requires only 38 repetitions if they are spread out over three days. A more complex subject which requires 504 repetitions in one day could be mastered by repeating it 158 times the first day, 109 times the second day, and 75 times the third day.
Thus, repetitions for all three consecutive days add up to 342, effecting a saving of time amounting to approximately 30 percent, if compared with the 504 repetitions on a single day.
Since time is, or should be, of great value to all of us, nobody should fail to make use of such time-saving device, especially if it is so easy to apply as the proper spacing of learning and repetition.
Whenever you have to learn something new, do not try to master it completely on the first day. Be satisfied if you acquire a fair knowledge of it, allow it to sink into your memory, and then repeat it on the two following days, and you will see that you can master it better with less effort.
It is one of the strange phenomena of the human mind that memory continues to work even when that actual task of learning has ceased and even when we are asleep. It is the same peculiar occurrence which helps us to solve a problem while we are dreaming, especially a problem on which we focused our attention before going to sleep and which proved too tough for solution.
The only explanation which is possible for both phenomena is the fact that our subconscious mind continues working and thinking while our conscious mind is asleep. The same mental power which produces dreams must be able to work on problems and to solve them. It is evidently wrong to think of our conscious and our subconscious functioning as two mental activities which are eternally divided. It is much better to think of them as two rooms whose separating wall is flexible and easily removable. It is figuratively accurate to speak of the “threshold” between the conscious and the subconscious mind, for every thought can easily lapse from the conscious to the subconscious, and we are sometimes able to draw a thought from the subconscious over this threshold into the conscious mind.
I am sure this has happened to you as it has happened to me and to everybody else. We try to think of the name of a person and cannot remember it. We have known this person for a long time, but at the moment the name does not come to us. It is not in the realm of consciousness. However, if at that moment we hear or read a name which is similar in sound or which has some other association to the name in question, then this similarity will be enough to recall the name to our conscious mind.
What happened in between? We know that no impression which ever meets one of our five senses can be entirely lost. While we are not aware of it, it rests in our subconscious, where it may be buried for good or whence we may be able to draw it over the threshold into our conscious mind, usually with the help of some association.
It is about the same procedure that takes place in a dream or under hypnosis. When somebody awakes from sleep or from hypnosis, which is nothing but an artificial sleep, he may not recall anything that happened. This, however, does not mean that impressions received under hypnosis are entirely lost. They may lie dormant in his subconscious and may be drawn over the threshold voluntarily or involuntarily by proper association.
From the book Stop Forgetting by Dr. Bruno Furst, 1964.