What is it
The human brain builds wiring through repetition. If I tell you the atomic mass of lead is 207.2, you may remember it 2 minutes from now, but probably not five, and certainly not tomorrow. To remember the atomic mass of lead, you may need a reminder in 2 minutes, but then you’ll have learned it twice, so you can hold it in your memory for 5 minutes before needing another reminder. If you get another reminder at 5 minutes, it will stick, but if you wait 6 minutes it will have slipped from your mind. (timing approximate) It’s also not effective to simply repeat the information 10 times in a row; there needs to be time between the repetitions in order to build the pattern. It’s more effective to learn it once a day for 10 days, than 10 times in a minute. Spaced repetition capitalizes on the idea that the more you already know something, the longer you can go before needing a reminder of it, so instead of a fixed interval, it uses an adaptive interval. Spaced repetition waits until just before you forget something to quiz you on it, not too often (so it doesn’t waste time) and not too infrequent (so you don’t forget it).
How to do it
There are a lot of algorithms out there for approximating the optimal schedule of reminders. A baseline suggestion would be 1 day, 7 days, 16 days, 35 days. If you struggle to remember something, shorten the next reminder interval. If you forget it completely, shorten the interval even more.
It can be difficult to keep track of exactly when each concept or fact needs to be reminded. Computers are really good at remembering to remind humans of things. Software like anki can be used to great effect, and can be tuned to fit the needs of the individual learner and topic. If you can do a lot of concept-chaining, you may be able to use wider intervals and save yourself studying time. If the material is dense, difficult, and unfamiliar, using narrower intervals may be more beneficial.
When to apply it
Any time that you need to retain information. While it can be useful for concepts, spaced repetition is a memorization scheme more than anything, and lends itself more to remembering facts. For example, it’s great for learning language vocabulary.
Bibliography
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