Hacking memorization with Spaced Repetition

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This post is part of the Study Hacks series, written by Reed Rosenbluth.

If you’re like me, you despise memorizing things. After all, it was Einstein who said “Never memorize something that you can look up.” Yet unfortunately, us students are often put in situations where memorization can make our lives significantly easier. While I don’t believe that memorization should ever be used as a students first weapon of choice, learning how to take advantage of a technique called Spaced Repetition can certainly come in handy.

The method of studying you are about to learn exploits something called the spacing effect, initially observed in 1885 by a German psychologist, to achieve results much better than conventional studying techniques. The spacing effect essentially says that if you can only study the answer to a question, say, 5 times, then your memory of the answer will be strongest if you spread your 5 tries out over a long period of time. The worst thing you can do is blow your 5 tries within a day or two.

So why do students bother cramming the night before the test, when they can practice Spaced Repetition. Because cramming does work. It’s true, through cramming, you can memorize quite well, but only for a short amount of time. When cramming, you trade a strong memory now for a weak memory later, and since tests are usually based on new material with the occasional old question cramming has become very popular amongst students.

But cramming is short sighted, and ignorant of the advantages of Spaced Repetition. “Knowledge builds on knowledge; one is not learning independent bits of trivia” says Gwern Branwen in his in depth article about Spaced Repetition. According to memory research forgetting happens exponentially, following a predictable curve that varies from item to item. An item that you remember well has a flatter forgetting curve than an item you remember weakly. For example, you recall a fact without any effort, and give yourself a grade “A”. Next you recall a second fact, but only after putting in some effort, so you give yourself a grade “C”. The forgetting curve would predict that you would completely forget the grade “C” fact days before you would completely forget the grade “A” fact. Spaced Repetition techniques schedule an item for review right before the forgetting curve predicts you would have less-than-perfect recall. Not only does this minimize the number of items you need to review, but it also minimizes the number of reviews for each item.

Looking back, it is easy to see why cramming is so popular and Spaced Repetition isn’t. The payoff of Spaced Repetition is distant and unobvious and it requires a good deal of self control. In addition to this, the technique is slightly more complicated than simply cramming. But once you get the hang of it, you will never want to go back. So lets jump right in.

The Technique

The optimal way to practice Spaced Repetition would be to review a flashcard until you know it and then review it again right before you are about to forget it. But that’s the problem. If you’re just about to forget about it, how are you supposed to remember to review it. This paradox is resolved by using software to remember what we need to review and when we need to review it.

The Software

  • Anki: flashcard software supporting images, audio, videos, scientific markup (via LaTeX). It also exists for almost every platform imagineable.
  • Mnemosyne Project: another free flashcard tool that uses Spaced Repetition.

Overall, I’d have to say that Anki wins the software battle. It’s algorithm for optimized card ordering is better and it even makes great looking graphs and pie-charts showing you your study patterns.

In conclusion, Spaced Repetition software is pretty awesome. It is based on a famous effect discovered by science, and does a very good job at exploiting it. As Gwern Branwen says “It’s a testament to the Enlightenment ideal of improving humanity through reason and overcoming our human flaws; the idea of Spaced Repetition is seductive in its mathematical rigor.”


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