What is spaced repetition?

In order to retain any information in our brain we must refresh it periodically. Let’s assume that you hear somewhere the following fact: “The capital of Norway is Oslo”. If you are not using this information in any way, you will most likely forget it after a very short amount of time. If, however, you encounter this information again and again, for example because you might have an interest in Norway or you happen to visit Oslo from time to time, or you learn for an exam on Northern European geography then obviously you will remember this information for much longer time.

The more often you have encountered a piece of information the less often you need to refresh it to keep it in your memory. However, even the most familiar information will be forgotten if it is not encountered or refreshed for a very long time. It is for example not uncommon that people who move to another country will over longer periods of time loose their ability to speak their own mother tongue properly.

Most likely, everybody has made a similar experience. When you were using some piece of information actively it was always easy to recall. However, once you stopped using it, since it was not important any more in your daily life this information quickly faded away until it was completely forgotten.

Spaced repetition is a learning technique that is based on these facts. It means that you review information at gradually increasing intervals.

Spaced repetition is sometimes also called spaced rehearsal or expanding rehearsals. Even more alternative names are graduated intervals, repetition spacing, repetition scheduling or spaced/expanded retrieval.

The Leitner System

In combination with flashcards (see what is a flashcard) spaced repetition creates an way of optimizing your learning. In the 1970s Sebastian Leitner conducted a series of experiments for improving his own learning behavior and subsequently developed the Leitner-System.

The Leitner System can be viewed as a physical box in which you store your flashcards. The box has several compartments labeled e.g. 1 to 5 (you could choose more compartments as well). You then put each of your flashcards into appropriate compartments in this box. If your flashcard is still new you will want to put it in the first compartment, where you repeat the flashcards every day. Flashcards, which you know well will be put into the second compartment. Flashcards in the second compartment have to be reviewed every second day. Flashcards, which you know well there will be moved to the third compartment and so on. Each compartment has a different repetition interval. And flashcards, which you know well, get promoted to the next compartment.
In case that you could not answer a flashcard correctly you move it back to the first compartment where the cycle starts again.

With this system you are able to sort your flashcards into those you know well and those, which are difficult to retain or you don’t know well.

Thus you study the flashcards, which you know worse more often.

Now onto the bigger problem: how often do you have to repeat the flashcards in each compartment?

Obviously there are a couple of problems with the Leitner System.

• What intervals should the compartments have? Should the second compartment be 2 days or maybe 5 days? What about the third, fourth, fifth etc. compartment? You might find a solution, which works for you with a lot of trial and error.
• You repeat too much! Let’s assume you put some flashcards from the second compartment to the third one with intervals of 2 and 5 days respectively. Now since you look at the third compartment only every 5 days but can put flashcards from the second to the third at day 1, 3 and 5 the flashcards in the third compartment did not actually have a 5 days interval. Sure, some of them did, but for most of them the interval is smaller than 5 days, so you do a lot of additional repetition, which is a waste of time.
• In principle, each flashcard needs to have its own box with compartments. However even this is not enough. The Leitner-System does not take into account your past performance of this card. Each time you answer the cards incorrectly the appropriate optimal spacing intervals for each card must be adjusted as well.
• You have to do some management overhead, since you have to keep track which compartment have to be repeated on which day.
• If you want to use the Leitner System with physical flashcards you also will have another problem: this system can be easily used for a couple of hundred flashcards, however things get rather messy if you have thousands or tens of thousands of flashcards.

In order to spend as little time as possible on learning and repetition we have to attribute to each flashcard its own repetition schedule. The Leitner System does not capture this easily since it has only 5 (or maybe some more) rigid compartments available.

Automatic spaced repetition scheduling

Here is where the computer really shines.

The combination of spaced repetition, flashcards and computers leads to the most optimal way of learning. The computer manages and calculates for each individual flashcard the optimal repetition interval based on your past performance of that particular flashcard. No more rigid compartments as in the Leitner System, no more guessing about the correct interval timing, no more management overhead. Spaced repetition software (SRS) increases the efficiency of studying with flashcards with sophisticated adaptive spaced repetition algorithms, which track your repetition performance for each flashcard in the database individually.

Computer based spaced repetition flashcard software therefore drastically reduces the time to learn information that can be arranged in question/answer pairs.

How can we optimize the learning process?

The two main factors for your success in learning and retaining the information are:

1. How much of the information do you still retain?
2. How much time and effort did you spend to reach and maintain your current level of information retention?

Obviously you will want to retain as much information as possible (1) but with a minimum investment of effort and time (2).

You could review the capital of Norway every minute, or every hour or every day. But what for? If your reviewing does not add to any increase in your level of knowledge, you are simply wasting time and manpower.

Optimizing learning means that we want to make as few repetitions as possible to reap the maximum benefit out of it. We want to spend the minimum amount of time to learn any piece of information such that it permanently stays in our memory. All the time you spare not repeating things you already know well you can either enjoy with your family and friends or learn new things to increase your level of knowledge. Learn more in less time.

We want to repeat frequently enough that we don’t forget any of the information. But we also want to review as infrequently as possible so as not to waste valuable time.
We want the repetitions to occur exactly at the sweet spot where we just still know the information before it is forgotten.

The task of the spaced repetition algorithm is to determine the optimal repetition spacing interval for a given flashcard.

So how does spaced repetition work from the user’s perspective?

Flashcard Learner is a flashcard software with an adaptive spaced repetition algorithm. After you have downloaded and installed it, you can start learning and repeating your flashcards or you can test the software with the included sample data bases. The general procedure is as follows:

1. Each day, check Flashcard Learner: it will present you with a list of flashcards, which have been scheduled for repetition on that day.
2. You then try to recall the correct answer from memory for the flashcards.
3. For each flashcard Flashcard Learner will show you the answer and you rate your performance on this flashcard. The rating process is not just right or wrong, but you should indicate the difficulty level of answering the flashcard.
4. Flashcard Learner then schedules the flashcard to be repeated again at some point in the future based on your rating of your performance that day and on your previous performance of the flashcard.
5. Steps 2-4 are repeated until all items are reviewed.
6. The flashcards, which were easy for you to answer, will be scheduled further into the future than the ones which you had difficulties with — those are repeated more frequently until you know them sufficiently well.
7. If you use Flashcard Learner regularly it will adapt to your unique learning style and abilities and will be able to predict more and more accurately for each individual flashcard the ideal repetition interval. So you don’t need to worry any more about repetition schedule. Flashcard Learner makes sure that all the items in the database will enter smoothly and effortlessly into your long term memory.

Flashcard Learner uses two different modes: the Learning mode and the Repetition mode.
Learning serves as entering flashcards into the scheduling process of the spaced repetition algorithm.

On a typical day of use you first repeat all the items that are scheduled for today. If you still have free capacities and want to move on in your studies you would then learn some more items from the unlearned items in your database, which will then move to the regular reviewing intervals of the repetition mode.

Spaced repetition software engages you in an active reviewing process, since it always expects you to provide an answer. So your brain has to remember correctly the asked piece of information, which in turn activates and strengthens neural connections. Passive reviewing, such as simply re-reading material is much less effective.

The advantage of spaced repetition software (SRS) is that it automatically manages and schedules revisions in your learning process. Therefore you can focus on difficult items and don’t waste valuable learning time repeating items, which you know already very well.