2 0 1 1 年 1 0 月 5 日

What is SRS learning? Spaced Repetition System


The way a lot of people memorise stuff is to make a long list of prompts, then repeatedly run down the list checking that they can recall each item. This is how I started off memorising Chinese characters. I lasted about two days.

A flashcard system

This method is outrageously slow and inefficient. Even if you’ve only got 100 items on your list (and character lists will run into the thousands within a year or two of study), and there’s just one item you don’t know, you have to go through the entire list to find it.

If the list is long, by the time you’ve gone through it once you’ve probably forgotten half of the items on the way. This is obviously crap.

Spaced learning: a better way

Step in SRS – a spaced repetition system. On the very first run through, this system is actually the same as the one described above. You go through and mark any items you don’t know.

Every time after that, though, the system works its magic. In the second review session, the system will only ask you to remember the stuff you forgot last time.

So in the example with 1 item in a list of 100, you’d only need to do that one item. SRS would be one hundred times faster.

Intelligent scheduling

SRS is actually cleverer still though. It doesn’t just keep track of what you forget and what you remember. It also predicts when you’re most likely to forget things, based on a mathematical formula plus information it gathers as you study. It can then intelligently schedule items to be reviewed at the most efficient time possible: just before you forget them.

So each time you use the SRS system, it shows you what you really should be studying at that moment. This frees you up to focus entirely on studying. The system handles all of the scheduling and arranging for you.

Ye Olde Flashcards

A set of flashcards

At first SRS systems were actually implemented with real, physical flashcards. This was still a huge step up from rote learning, but couldn’t quite take advantage of the full implications of SRS.

Now with spaced repetition software, the computer can not only handle all of the calculations, but do it in incredible detail, taking into account a wide array of information to optimise your study time.

That means you can achieve more in the same amount of time, or spend less time and not fall behind in your studies.

The algorithm

There’s one algorithm used by pretty much all SRS software these days – the SuperMemo algorithm. This was thought up by a genius called Piotr A. Wozniak and is freely available online.

The idea is that as you go through your items to be memorised, you give each one a grade between 1 (embarrassing failure) and 4 (legendary success). Notice how you cay also rate your life on the same scale.

Stuff you remember easily gets pushed further and further into the future each time you get it right. So after correctly remembering it once, it’ll get scheduled for an hour in the future. Then a day, two days, a week, a month, a year etc.

Once you’ve been studying for a while, there’ll items several years ahead because you remember them so well (e.g. 你好).

Inversely, stuff you forget gets pulled closer towards you in the schedule. So if after a week you’ve forgotten an item, it’ll be rescheduled to be seen again in a day or two. If you forget it again after that gap, it’ll be pulled even closer to give you more chance.

The overall effect is that you spend the most time studying the things you need to spend time on, and very little time is wasted on stuff you’ve memorised successfully.

I asked Dr Wozniak about SRS, so, in his own words:

“In short: SRS is NOT BETTER than OTHER SYSTEMS. This is THE ONLY system. This is simply how memory works. Either you do a spaced repetition or you lose a memory trace (or, worse, waste time on unnecessary, or even harmful repetition).”

Why this is so great

The applications of this for language learning are obvious. Put all of your vocab into the SRS system, put some time in each day, and let the software handle the rest.

This is particularly true for East Asian languages, as characters make nice discrete units to be memorised. And that’s the sort of thing an SRS system does best.

Some caveats

I’ve been singing the praises of SRS up till now, and it is good. But a lot of learners drastically over-estimate what SRS can do when they first find out about it. I was a classic example of this. It’s easy to get into the mindset that all you have to do is mindlessly add things to the system and it it will magically make you learn it.

Apart from the fact that ultimately you still have to put the hours in to memorise stuff (SRS just makes it more efficient), over-adding vocabulary quickly makes doing your reviews tedious and time-consuming. Try to keep the deck trimmed to a minimum unless you really want to put in hours every day.

Also remember that your brain is extremely good at learning in context. A lot of people find, myself included, that even though you can easily remember an item when reviewing it in the SRS system, when it comes to actually use it in real life it’s not so easy. This is why no matter how good your reviewing system is, you’ve still go to get out there and really use a language.

Well, until VR language training gets invented.

The best SRS software:

Skritter

My personal favourite for studying Chinese and Japanese vocabulary. There’s a subscription charge, but in return you get a lot of automatic, helpful features so you can focus on actual studying.

Anki

The most popular free SRS software. Very customisable and versatile. I got in contact with Damien Elmes, the guy who programs Anki:

“I had been studying Japanese on and off, but found it pretty frustrating, as I was forgetting almost as much as I was learning. When a friend introduced me to the concept of spaced repetition, I was blown away by the idea. Suddenly my studies became much more productive, and I felt like I was really retaining things for the first time.

Anki started out of a desire for particular features that didn’t exist in other flashcard apps, like synchronization between machines and support for automatically entering the reading of Japanese characters. It was initially just a hobby project, and at the time I never imagined I’d one day be working on it full time!”

SuperMemo

This is the original SRS software, designed by Dr Wozniak. The algorithm he has released publicly is actually an old version – the only way to get the latest one is to purchase this program. From Dr Wozniak again:

“As for SuperMemo, my answer is obviously biased, it is the by far the best just because it has been tested and overanalyzed over the years (25 and counting). The amount of work needed for such analysis makes it simpler for other developers to simply use one of the old SuperMemo algorithms, which, you guess, are a bit old .. :)”

 

A similar article is available on YingFish.com in Chinese: 什么是 “SRS” 软件? 记忆重复软件

SRS explained on other sites:


Tags

The article 'What is SRS learning? Spaced Repetition System' has the following tags (click a tag for more articles on that topic):