Forget nothing: Spaced repetition for infinite memory

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Memory is a black hole.

You don’t notice when you’re in school. Then, memory is merely a sparring partner. It shows up at scheduled intervals to challenge you. A quiz, a test, a final exam. Sometimes you win. You pass the test, you pass the class. Sometimes you lose. Memory pats you on the shoulder and says “better luck next time.”

But one day your sparring partner stops showing up.

You’re done with school. No more classes. No more tests. But you feel no loss as you plunge into the next phase of your life. New challenges, new topics, new skills.

New, new, new.

But what about the old?

You won’t notice it at first. If you’re working in the field you studied you will continue to use that knowledge and it will strengthen and grow. But given time and neglect, any knowledge that you once had fresh in your mind will fade.

You’ll forget what happened in books you once loved.

You’ll forget the details of subjects you once knew.

You’ll forget conversations you once had and the people you had them with.

This process isn’t alarming until the moment you’re confronted with the gap—the gap between what you know you learned and what you actually know. The moment you think back to a semester of early morning classes, getting up early, walking across campus, settling down in your creaky desk, and learning… what?

An entire semester of learning, gone.

Memory is a black hole. That scares me to death and it should scare you. Without your sparring partner, without continual practice, you will forget everything that you do not use. We don’t know we’ve paid that price until we’ve paid it.

Time gets the blame, but time just cleans up the trash that your brain puts on the curb. You discard your own memories through neglect. If you want to stem the tide, you need to entrust your memories to a system for safekeeping.

An old friend to the rescue

Flashcards are nothing new. You may have used them to learn vocabulary words or practice for a test.

If you’re cramming for a test you might take a card, write a term on the front and its definition on the back.

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You make more cards until you’ve covered the scope of the test. Before the test, you look at the front of every card, get yourself to recite the definition without looking, then check the back. You keep going until you can make it through the entire deck without errors.

The result? From the moment you put down your deck of cards and breathe a satisfied sigh, you have mastered its content. No one can stump you! Consider this test “studied for”.

But before your cards hit the desk, that knowledge begins to fade. Maybe you’ll keep it fresh for 30 minutes, maybe a few hours. (At least until you can finish the test!) And the ‘A’ you receive on it will justify your effort. But just a few days later you will have forgotten.

Back in 1885, Hermann Ebbinghaus was the first to study and graph the rate we forget new knowledge. According to his "forgetting curve," we lose about 70% within a few short days, with the remaining 30% inevitably fading later on.

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Is it any wonder freshman Philosophy class is a blur?

The tragedy is that those flashcards could do so much more. The secret is spaced repetition.

Spaced repetition

What if instead of tossing out your flashcards after your final exam, you kept them? Go ahead, throw out the cards that you honestly don’t care if you forget. But keep the rest.

What if you reviewed your flashcards again, right before you were about to forget everything? Say, two days after your first review. You would find it slightly difficult but you would quickly get back up to speed.

“Well sure, I could keep studying my flashcards every two days for the rest of my life. But who is willing to do that?”

The beauty is that every review will cement the memory in your mind a little longer.

What’s important is that you review right when you’re at the cusp of forgetting. If you last studied a flashcard two days ago, you could study it again in ten days. You would likely find the task as difficult as the last time, even though the interval was five times as long. And this trend—holding memories in your brain for longer and longer—will continue.

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Eventually you’ll have intervals of 4 months, 2 years, 10 years! Each time you study you’ll notice some memories that you’ve forgotten. But by reviewing you can prevent those memories from fading silently away and instead build them back up.

Does it take effort? Absolutely. But compare it to the effort you spent to learn that information in the first place. By spending a fraction of that original time you can keep that knowledge in your brain for the rest of your life, instead of losing it to the black hole of memory.

Software solutions

I don’t honestly propose that you use paper flashcards. They’re hard to make, alter, and store. But the biggest problem is that they're difficult to use with spaced repetition. You’ll probably have an easier time remembering what a femur bone is compared to a lacrimal bone. You shouldn’t be looking at the femur card as often as the lacrimal card.

Here is where software can help. There are a number of great, free spaced repetition solutions out there. I use Anki, but Mnemosyne, SuperMemo, and Memrise are other popular ones. They work by tracking each fact separately. When you correctly answer a card, the interval increases. If you get it wrong, the interval resets. This way, you only focus on the facts that need your attention, and the easier facts will wait long enough to give you an adequate challenge.

But all facts will come back, and there’s great comfort in that. I have some cards in my deck which are set to reappear in over two years. These are cards that I feel very confident about now. But will I remember them in two years? I don’t need to worry. By committing to spend a few minutes each day studying flashcards, I know that I’ll be quizzed on that fact right when I’m about to forget it.

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Spaced repetition is simple but powerful. It’s just the old adage “review what you study” augmented with some powerful cognitive neuroscience. But the benefit is clear—it gives us humans a fighting chance against the black hole of forgetting.