Spaced Repetition

Spaced repetition is a scientific learning method that combines active recall with properly timed review sessions. Extensive research has shown that this method can significantly improve long-term memory retention, making knowledge truly stick in your mind.

What is Spaced Repetition

Simply put, spaced repetition means reviewing just before you're about to forget. When you first learn a knowledge point, your brain forms an initial memory. But without timely review, this memory gradually fades until it's completely forgotten.

The core idea of spaced repetition is to review at the right time when memory starts to decline but hasn't completely disappeared. After each review, the memory becomes more solid and can last longer. After several repetitions, knowledge can truly become long-term memory.

The Law of Forgetting

Over a century ago, German psychologist Hermann Ebbinghaus discovered the law of human memory forgetting through extensive experiments. He found that newly learned content is mostly forgotten after one day, but if reviewed in time, the rate of forgetting slows significantly.

This law was later plotted as a curve called the "Ebbinghaus Forgetting Curve." It clearly shows how memory declines over time: within one day after learning, the rate of forgetting is fastest; then it gradually slows, but without review, it will eventually be completely forgotten.

Through this curve, we can see that if you review when memory is about to fade, it takes only a short time to restore it; but if you wait until it's completely forgotten, you have to start over, greatly reducing efficiency.

How Spaced Repetition Works

Spaced repetition has two key mechanisms at play:

Spacing Effect

Research has found that the same content, studied over several days, produces much better results than studying it concentrated in one session. This is because the brain needs time to consolidate memories. Leaving intervals between study sessions gives the brain enough time to establish strong neural connections.

Active Recall

Spaced repetition emphasizes active recall, not passive re-reading. When you try to recall a knowledge point, your brain performs deeper processing, creating much more profound memories than passive reading. Like physical exercise, active recall "exercises" your memory ability.

The Effects of Spaced Repetition

Scientific research shows that proper use of spaced repetition can increase memory retention by 200% to 400%. This means that with the same study time, you can remember significantly more content.

More importantly, spaced repetition helps you transform knowledge into long-term memory. Short-term memories are easily forgotten, but through scientific spaced review, knowledge gradually becomes long-term memory that you can access anytime, truly becoming part of your knowledge system.

The Evolution of Spaced Repetition Algorithms

As technology has developed, spaced repetition has evolved from manually scheduling reviews to algorithms that automatically calculate optimal review times.

Early algorithms like SM-2 (used by SuperMemo 2), while effective, were not precise enough. Later algorithms like SM-17, SM-18, and the latest FSRS (Free Spaced Repetition Scheduler) algorithm have continuously optimized to make review timing predictions more accurate.

These algorithms analyze your learning situation: what content you master well, what's easily forgotten, then calculate the most suitable review time for each knowledge point. Content you master well will have increasingly longer intervals; content that's easily forgotten will prompt you to review at critical moments.

Application in Noolingo

Noolingo uses the FSRS (Free Spaced Repetition Scheduler) algorithm, a modern spaced repetition algorithm based on machine learning. Compared to the traditional SM-2 algorithm, FSRS can more accurately predict the optimal review time for each knowledge point by analyzing vast amounts of user learning data.

The advantage of the FSRS algorithm lies in its accuracy. In benchmark tests, FSRS's root mean square error (RMSE) in predicting memory retention is significantly lower than traditional algorithms, meaning it can more accurately determine when you'll start to forget and schedule reviews at the best time. This precision not only improves memory effectiveness but also reduces unnecessary repeated reviews, making your learning more efficient.

More importantly, FSRS dynamically adjusts your review schedule based on your personal learning history. The system analyzes your memory performance: what content you master well, what's easily forgotten, then calculates the most suitable review interval for each knowledge point. Even when you're just starting out with limited data, FSRS can provide better review arrangements than traditional algorithms through default parameters.

You don't need to calculate when to review yourself, nor worry about forgetting important content. Noolingo's FSRS algorithm will arrange everything for you, letting you focus on learning and thinking without worrying about memory issues.

If you want to learn more about the technical details and research results of the FSRS algorithm, you can refer to relevant academic papers and research materials (in English).