Epistemic status: splitting hairs. Originally published as a shortform; thanks @Arjun Panickssery for telling me to publish this as a full post.

There’s been a lot of recent work on memory. This is great, but popular communication of that progress consistently mixes up active recall and spaced repetition. That consistently bugged me — hence this piece.

If you already have a good understanding of active recall and spaced repetition, skim sections I and II, then skip to section III.

Note: this piece doesn’t meticulously cite sources, and will probably be slightly out of date in a few years. I link to some great posts that have far more technical substance at the end, if you’re interested in learning more & actually reading the literature.

I. Active Recall

When you want to learn some new topic, or review something you’ve previously learned, you have different strategies at your disposal. Some examples:

Watch a YouTube video on the topic.
Do practice problems.
Review notes you’d previously taken.
Try to explain the topic to a friend.
etc

Some of these boil down to “stuff the information into your head” (YouTube video, reviewing notes) and others boil down to “do stuff that requires you to use/remember the information” (doing practice problems, explaining to a friend). Broadly speaking, the second category — doing stuff that requires you to actively recall the information — is way, way more effective.

That’s called “active recall.”

II. (Efficiently) Spaced Repetition

After you learn something, you’re likely to forget it pretty quickly:

Fortunately, reviewing the thing you learned pushes you back up to 100% retention, and this happens each time you “repeat” a review:

That’s a lot better!

…but that’s also a lot of work. You have to review the thing you learned in intervals, which takes time/effort. So, how can you do the least the number of repetitions to keep your retention as high as possible? In other words — what should be the size of the intervals? Should you space them out every day? Every week? Should you change the size of the spaces between repetitions? How?

As it turns out, efficiently spacing out repetitions of reviews is a pretty well-studied problem. The answer is “riiiight before you’re about to forget it:”

Generally speaking, you should do a review right before it crosses some threshold for retention. What that threshold actually is depends on some fiddly details, ...

Saul Munn's Shortform

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Saul Munn's Shortform

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