Spaced repetition has a very long history with hundreds of papers published on the topic. Here's a good survey of some of the published research https://gwern.n

Spaced repetition has a very long history with hundreds of papers published on the topic. Here's a good survey of some of the published research https://gwern.net/spaced-repetition#background-testing-works https://gwern.net/spaced-repetition#background-testing-works