What is Spaced-Repetition?
If you have been trying to learn something new, you would know how frustrated it can be when you try to recall a specific piece of information and your brain goes blank. Memory failure is the arch-enemy of learning. There is no doubt about that.
Fortunately, there are ways to overcome the problem of memory failure and one of them is repetition. I know it sounds very basic. But basic stuff often works. And I am sure you have heard the saying which states “Repetition is the mother of all skills”.
If repeat the same action or review the same information over and over, you can certainly remember it for a very long time. But the problem with this approach is that it can become very impractical when there is large amount of information to be learnt. Reviewing one foreign word 10 times probably only takes you less than a minute. However, trying to do the same for 1000 words can take you a significant amount of time and heaps of mental energy.
In fact, to be able to remember anything for long term, you never need to rely on such a tedious approach. Your memory fades quickly after the initial exposure, which means you need to revisit it more frequently during the first few day. But the forgetting process bottoms out after a while, which means you don’t need to review it as much.
Based on this phenomenon, the concept of Spaced-repetition was born. In short, spaced-repetition is a principle which exploits the spacing effect of the memory by gradually increasing the time intervals between subsequent revisions.
It was first proposed by Professor Mace in 1932 in his book Psychology of Study. He introduced a simple revision pattern of doubling the time interval during each subsequent revision. For example, if you have learnt something today, your next revision should occur the next day. The second revision would be at two days after the first one, and the third revision should be at four days after the second revision, and it goes on like that.
Later other researchers in the field came up with different revision patterns. Paul Pimsleur published the “Graduated-interval recall” in 1967 which specified a rehearsal pattern of 5 seconds, 25 seconds, 2 minutes, 10 minutes, 1 hour, 5 hours, 1 day, 5 days, 25 days, 4 months and finally 2 years.
Although it was a much more complicated revision schedule in comparison to Mace’s system, it was applied specially to the programmed audio instruction in Pimsleur language learning system. Each audio instruction is generally very short ranging from seconds to minutes in timing. For that reason, Pimsleur’s pattern can be manageable.
But for other types of information which takes longer to go over each time, Pimsleur’s tight schedule may not be practical.
Another popular scheduling system is the Leitner system, which was invented by a German science populariser named Sebastian Leitner in 1973. It was a simple system involving flashcards and some boxes.
The number of boxes is generally arbitrary. The most common one is the 5-box system with each box representing a different revision schedule. For example, you may choose to study the flashcards contained in the first box once every day. Study those in box 2 once every 3 days, and box 3 every 5 days and so on.
While studying the cards, if a flashcard is answered correctly, it gets promoted into the next box. On the other hand, if a card is answered wrongly, it is demoted into the first box. Although a variation of the system also exists which promotes the card into a previous box instead of all the way back to the first one.
What happens when a card in the last box is correctly answered? It is generally taken out the last box and put away and no further revision is needed. Can it still be forgotten in the future? Absolutely. The Leitner system does not guarantee 100% retention rate long term. But it does help the learner remember most of the information learnt through this system.
Spaced-repetition is a well-established principle to convert information to knowledge which you will be able to retain for long term. There are a variety of revision or rehearsal schedules all aiming to achieve the maximum retention of information with minimal time investment. Despite all the studies done on this subject, there is lack of consensus on the exact interval pattern.
My feeling is all rehearsal patterns would work if you could learn to apply the principle to all your learning effort.