Spaced repetition

In 1885, the German psychologist Hermann Ebbinghaus ran one of the first controlled experiments on memory. He memorised lists of nonsense syllables and tested himself at intervals to see how quickly he forgot them. His results revealed a steep forgetting curve: within hours of learning something, most of it fades unless you review it.

But Ebbinghaus discovered something else, too. If he reviewed the material at the right moments — not immediately, but just before the memory faded too far — the forgetting curve flattened out. Each review made the memory last longer than the one before. With well-timed reviews, he could remember things for weeks with very little total study time.

This is the spacing effect, and it has been replicated hundreds of times since then, across almost every domain: language learning, medical training, motor skills, and yes, music. A major meta-analysis by Donovan and Radosevich (1999) synthesised 116 studies and found a meaningful effect size (d = 0.42), meaning spaced practice reliably outperforms massed practice — even when total study time is the same.

When you first learn a passage, your memory of it is strong but fragile. Over hours and days, the trace decays — this is the forgetting curve. If you wait too long to review, the trace is gone and you have to start over from scratch.

But if you review while the trace is still partially intact, something powerful happens: the act of retrieving the memory from long-term storage strengthens it far more than the original learning did. The next forgetting curve is shallower. Review again at the right time, and it gets shallower still.

The chart below lets you see this in action. The grey line shows what happens with no reviews: a steep, rapid decline. The coloured line shows how each review bumps retention back up and slows the next decline.

If you’ve ever drilled a passage for an hour and felt confident, you’ve experienced what researchers call the illusion of fluency. Massed repetition (doing something many times in a row) creates a powerful feeling of mastery. During the session, your performance might even be better than it would be under a spaced schedule.

The problem shows up later. On a delayed test — a day, a week, or a month after the practice — the spaced group consistently remembers more. The massed group feels like they “knew it” yesterday, but the memory didn’t transfer to long-term storage because they never had to retrieve it from there.

For musicians, this is especially important. You don’t perform the same day you practise. You need the memory to last until the recital, the lesson, or the next session — and well beyond.

Music blends massed and spaced work in a way that’s unique. You need enough contiguous repetitions to actually shape a phrase — you can’t learn a difficult passage by playing it once a week. But to keep that progress, you need to revisit the passage on a schedule, spread across days and weeks.

The practical challenge is tracking all of this. If you have 10 pieces with dozens of passages each, it’s nearly impossible to remember which passages are due for review and which are still fresh. That’s exactly what spaced-repetition software does: it handles the calendar so you can focus on listening and playing.