What is Spaced Repetition and How Does it Work?

Digging into the basic concepts and understanding what we're actually doing when we practice spaced repetition.

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In this video we’re going to dig a little deeper into the concepts and learn where spaced repetition came from and how it works. 

In a nutshell, spaced repetition is based on the idea that the best time to remember something is right before you’re about to forget it. 

This also means that you shouldn’t waste your time trying to memorize things that you already know, and that it doesn’t really make sense to memorize the same piece of information every day at the same time. 

At this point I think that it’s important to note that what we’re concerned with here is retention, not learning. As I’ll explain later, you shouldn’t really be trying to memorize things that you don’t understand. 

So let’s begin by taking a look at where spaced repetition came from. 

Back in the late 1800s, a German philosopher by the name of Hermann Ebbinghaus was trying to understand how human memory works. 

In particular, he wanted to isolate the processes of “learning” and “forgetting” so that he could figure out how each of them works. If he knew how they worked, he could optimize for them. 

Ebbinghaus had a sneaking suspicion that memory of particular words would be impacted by pre-existing associations: things like personal memories, experiences, or general vocabulary.

He was right. You’re probably able to recall your dad’s name more quickly than you can the barista who makes your morning coffee. That’s because you hear your dads name more often — said another way, the frequency is higher. 

Now imagine that the barista had the same name as your dad. You’d probably be able to remember it better. That’s one of the associations Ebbinghaus was talking about. 

So to avoid this, Ebbinghaus made up a whole bunch of words, about 2300 actually, from fairly random syllables called CVCs (stands for Consonant–Vowel–Consonant). 

Here are a few of his words: 

Next, he fired up a metronome and read them outloud, one after another.

After he was through, he’d try to recall as many as he could. What he found was that he forgot things at an exponential rate. 

On a graph, it looks like this: 

forgetting reviewed

The sharpest decline occurs in the first twenty minutes and the decay is significant through the first hour. The curve levels off after about one day.

However, and lucky for us, once we forget something it’s easier to re-learn it. This is called the learning curve, and it’s the 2nd thing that Ebbinghaus figured out. It’s pretty much exactly the same idea. 

Left Compare learning curve of agents without skill between task1 and task2 Right

The first time you learn information you take in the lions share and each subsequent time you actually leave with smaller and smaller amounts on top of that base. 

Anyway, back to memory. 

The end result of this research was that the best way to strengthen the memory of learned information was to engage in spaced repetition based on active recall. 

Active recall is when you see a question and have to come up with an answer without any help. In contrast, passive recall is something like reading, or multiple choice, where the answer is there and doesn’t have to be produced out of thin air. 

As we posited before, the best time to learn something is just before you’re about to forget it. If we look back to the forgetting curve we can see that each time we repeat the active recall process the curve flattens a little and we slow down the process of forgetting. That’s because every time we recall something we strengthen the memory. 

Each time we strengthen something we can wait a little bit longer to recall it. That is the space in spaced repetition. 

The important principle here is that for long term memory it’s not the number of times that we recall something, it’s the period of time over which we continue to access the information. 

That’s how we make sure we remember something long-term — by remembering it every once in a while when we’re just about to forget it. 

This is what spaced repetition does — and believe me, it works like a charm. 

After I explain this to people, they’re often incredulous. It can’t possibly work, or we’d all have heard of it. 

I know. It’s kind of nuts. And by the way, you’re not the only one who thinks that.. 

In 1988 a leading psych journal published a piece called “The Spacing Effect: A Case Study in the Failure to Apply the Results of Psychological Research.”

Alright, now that we know what spaced repetition is and where it came from, we’re ready to get started. I’ll see you in the next video, where we’ll do just that.

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I'm a developer, marketer, and writer based in Appleton, Wisconsin.