How spaced repetition works
You remember something longer if you review it a few times, spread out, than if you review it many times in one sitting. Spaced repetition uses that: each review comes just before you would forget.
What Hippocampus does
- Each day, a deck adds a few new cards (you set how many) and brings back the cards that are due.
- For each card you answer Missed it, Almost or Got it. A card you get right comes back after a longer gap than last time. A card you miss comes back soon.
- Over a few weeks, the cards you know well show up rarely, and your daily session is mostly the cards you are still learning. Most sessions take a few minutes.
- When cards are due, Hippocampus reminds you by Discord direct message or email, inside the hours you choose.
The research
In 1885 Hermann Ebbinghaus measured how quickly he forgot lists he had learned, and found that forgetting is fast at first and then slows down: the forgetting curve. He also found that spreading practice out made the lists last longer.
Bahrick and Hall (1991) tested people on mathematics they had studied in school, up to 50 years earlier. Those who had studied it over several courses still knew much of it; those who had studied it once had mostly forgotten it.
Kornell (2009) had students learn vocabulary with flashcards, either spaced out or crammed. Spacing gave better results for 90% of the students, though most of them believed cramming had worked better.