Applying Spaced Repetition and Active Recall to Books to Hack Your Brain

One of my favorite scenes in The Matrix is when Tank the operator hooks up Neo to a brain-computer interface and starts uploading all kinds of skills directly into his mind. In seconds, Neo becomes a kung fu master.

I know kung fu

I've always imagined nonfiction books to be kind of like those hand-labeled "skill cartridges" scattered about the Nebuchadnezzar. After all, writing such a book is the act of compressing months if not years of accumulated knowledge, wisdom, and expertise into a cohesive text that can be consumed in mere hours.

The only problem with this comparison is that, unlike Neo in The Matrix, we quickly forget nearly everything we read. How many times have you read a book in pursuit of bettering some area of your life, imagining with anticipation the whole time how your future self would take advantage, and then, once you finished, promptly did nothing?

For example, many of us invested over ten hours into reading that book about how to schedule blocks of focus time, avoid distractions, and get into a deep flow state. Yet we still multitask, our iPhones aren't on grayscale, and our Google Calendars looks like an aborted game of Tetris.

Why does this happen? It's because what we read flows through us like sand through open fingers. So much human potential is stored in nonfiction books, but so little is realized due to mere forgetfulness.

This is the problem we're trying to solve with Readwise and we're one step closer thanks to a new feature called Mastery.

Mastery is our term for the one-two punch of active recall and spaced repetition applied to the notes and highlights you take while reading. Used together, these principles of cognitive science enable you to retain substantially more of what you read with significantly less effort.[1]

The rest of this article will show you how to start using Mastery to hack your brain like Neo in The Matrix.

What is active recall?

Active recall (also known as quizzing, testing, or retrieval) is the process by which we challenge our minds to retrieve a piece of information rather than passively reviewing or re-reading the same.

For example, let's say we're interested in the science of learning, so we want to commit the following fact from Make It Stick to memory:

In very short order we lose something like 70 percent of what we've just heard or read. After that, forgetting begins to slow, and the last 30 percent or so falls away more slowly, but the lesson is clear: a central challenge to improving the way we learn is finding a way to interrupt the process of forgetting.

The passive approach to remembering this information would be to simply re-read that passage from time to time. This is no doubt better than never revisiting the passage at all, but research has repeatedly shown that active recall testing is significantly more effective.

How could we transform this into active recall? One approach would be to convert the passage into a question and quiz yourself on the answer:

Question: According to Make It Stick, approximately how much of what we've just heard or read do we lose in very short order?

[commence active recall...]

Answer: 70%.

The power of this technique probably requires no further justification, but the scientific evidence backs it up. The key to learning more is forgetting less. The key to forgetting less is systematic review. And the best way to review is through active recall.

How does Readwise harness active recall?

Readwise enables you to easily convert your highlights into two forms of active recall: question & answer and cloze deletion.

The rephrasing of the Make It Stick quote above is often referred to as question & answer, or simply Q&A. While Q&A is the pinnacle of active recall, and therefore we can't not support it as part of the Mastery feature, it is somewhat effortful to create those question & answer pairs. Accordingly, you'll probably reserve Q&A for only the choicest highlights and the most impactful books.

difference between knohow and knowledge

As a more everyday alternative, you can also employ a deceptively simple technique known as cloze deletion. With cloze deletion, a salient keyword or keyphrase is hidden from the passage, giving you an opportunity to pause and consider the missing word. For example:

In very short order we lose something like [...] of what we've just heard or read. After that, forgetting begins to slow, and the last 30 percent or so falls away more slowly, but the lesson is clear: a central challenge to improving the way we learn is finding a way to interrupt the process of forgetting.

[commence active recall...]

Answer: 70%.

Cloze deletion is, of course, just a fancy way of saying fill-in-the-blank. This might seem a trivial tweak, but the simple act of hiding a word forces you to consider the surrounding context and search your mind for an answer. The hidden word itself isn't that important; it's the modest effort of being forced to think about what you'd otherwise passively read.

For example, from another study cited in Make It Stick:

... researchers showed that simply asking a subject to fill in a word's missing letters resulted in better memory of the word. Consider a list of word pairs. For a pair like foot-shoe, those who studied the pair intact had lower subsequent recall than those who studied the pair from a clue as obvious as foot-s__e. ... The modest effort required to generate the cued answer while studying the pairs strengthened memory of the target word tested later (shoe)."

That's active recall: the first leg of Mastery. Spaced repetition is the second.

What is spaced repetition?

Spaced repetition is a technique for spacing out of reviews of previously learned material according to an algorithm designed to optimize your limited time for review. Each time you review a piece of information, you supply feedback to that algorithm which estimates the optimal time to show you that information again.

Without getting too technical, if you deeply understand something, you don't need to be reminded of it that often whereas if you struggle with something, you need to be reminded of it more often. Further, each time you successfully recall something, your memory of that thing is strengthened, so the intervals between successive reviews become longer and longer.

Spaced repetition is the literal opposite of cramming which, we probably don't have to tell you, is a great way of passing a test but a terrible way of truly learning something.

How does Readwise harness spaced repetition?

From the very beginning, Readwise has leveraged the principle of spaced repetition to space out reviews of your highlights. But now, with Mastery, Readwise enables you to supply precise feedback ensuring you see better-than-average passages more often, less-than-average passages less often, and so on.

Using Mastery in Readwise

Getting started with Mastery is easy.

Whenever you come across a highlight you want to master, hit the Master button (or keyboard shortuct: m), choose either cloze deletion or Q&A, and convert the previously passive passage to active recall.

cloze deletion in Readwise

You'll then be prompted with the spaced repetition buttons. If you want to see the highlight soon — because it's particularly insightful, relevant to your life right now, or hard to remember — choose Soon. If you want to see the highlight again but there's no immediate urgency, choose Eventually.

You'll see this Mastery card again in your Daily Readwise in approximately one to four weeks (depending on the spaced repetition feedback you supplied and the precedence of your other Mastery cards).

reveal active recall phrase

Going forward, your Daily Readwise will be divided into two halves. The first half will contain unprocessed highlights which have never been reviewed before in Readwise or haven't been converted to Mastery cards. These highlights are resurfaced stochastically (i.e., at random).

Note that you can manually "tune" the probability weights for each book and article through your Preferences page, dialing in the random algorithm described above. If you have a significant number of highlights, this is highly recommended. Tuning is like setting up a custom algorithmic feed for your own material which can be tweaked over and over as your interests change.

tuning your books

The second half of your Daily Readwise will contain your Mastery cards. These are resurfaced according to a spaced repetition algorithm and presented in active recall form. As with the initial creation of the Mastery card, once you're finished each review, you provide spaced repetition feedback informing how soon and how often you'd like to see that card in the future.[2]

In addition to converting your highlights to Mastery cards during the Daily Readwise, you can also do so on a book-by-book or article-by-article basis. Reviewing all the highlights from a single book in chronological order, shortly after having finished it, is a particularly powerful method to integrate that book's takeaways into your life. We'll be adding to this functionality over time.

Retention is NOT memorization

One final word of caution:

The first time most people see Mastery in Readwise, they tend to assume it's about memorization. Sometimes they even assume it's about (gasp) rote memorization.

That's perfectly understandable. Mastery looks like flashcards and, unless you're one of the select few who keeps a commonplace book like Ryan Holiday or a Zettelkasten slip-box like Niklas Luhmann, your last exposure to flashcards was probably memorizing vocab words to score well on the SATs.

This is not that. We want to be clear: Mastery is not about memorization.

The point is not to memorize a text verbatim so you can pedantically rattle off some passage word-for-word at a cocktail party. (Even though that could be cool.)

No, the point is to reprogram your brain. To prime your mind to spot patterns, form connections, and resurface the right idea at the right time.

Let me give you an example.

When I first began experimenting with the prototype that evolved into Readwise, one of the first books I "mastered" was Deep Survival by Laurence Gonzales. It's about how people find themselves in "survival situations" and why so few get out.

As it turns out, one of the most common survival situations is hiking. Specifically, hikers who lose the trail because they fail to appreciate that way out will look different than the way in.

A few months after I'd read Deep Survival, I found myself nearing such a situation. I was two or three hours into one of those remote, four-hour hikes through the Costa Rican jungle, trying to find some Instagrammable waterfall, when gradually (not suddenly) the trail began to fade.

It was so impercepible that my former self would have never noticed. But somewhere, deep inside the recesses of my subconscious, a pattern was matched. This triggered a flood of cautionary tales from Deep Survival to be released in my mind.

"Slow down."

"Look for landmarks."

"Turn around and take note of the path on the way out."

We heeded this advice and cautiously proceeded until the trail reappeared. Disaster was averted. On the way out, I began to reflect on what had just happened.

There was no ruler-wielding teacher at the front of the classroom quizzing me on the periodic symbol for argon. No, this was something profound. Something intuitive.

The right ideas had popped into my head at exactly the right time, all as a result of a few minutes a day invested not only into reading books, but also into actively reviewing the best parts of those books.

This was — dare I say — wisdom.

The hike in Costa Rica was the first time I consciously noticed the phenomenon of the right idea from a book popping into my head at the right time. But afterwards, I started to notice it happening to me all the time, throughout the day, in a variety of contexts.

You can make this happen in your mind too, for any subject you want.

For example, if you apply Mastery to Deep Work and your weekly calendar starts to fill with shallow calls and meetings, your mind will likely notice the pattern and then start nudging you to create some uninterrupted space. Maybe I should schedule a four-hour focus block to protect that currently unoccupied Thursday morning?

If you apply Mastery to Triangle Selling and you revert to talking about features and benefits in a client pitch, your mind will likely call you out and then start nudging you to present your product using pain-based discovery questions including social proof and emotional words. Many of our customers are frustrated by the inefficiency of books because they spend all this time reading, but forget so much, leading to so little change. Does that resonate with you?

The sky is the limit.

Wrapping Up

Of course, the other problem with reading compared to the brain-computer interface in The Matrix is bandwidth. It takes much longer to read a book and then Master it using Readwise than it does for Tank to insert a cartridge and push the upload button. But until Elon Musk finishes his Neuralink, the combination of books, Readwise, and Mastery is one of the most effective techniques we've got.

  1. If you've heard of the popular spaced repetition flashcard software Anki, Mastery is kind of like that, but purpose-built for your highlights with a way shallower learning curve and much cleaner user experience. ↩︎

  2. For those spaced repetition geeks out there, we use an exponential decay algorithm, rather than a SuperMemo style scheduling technique, paired with our proprietary tuning. ↩︎

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