What the research found
Study spread out over days is remembered far longer than the same study crammed into one sitting. A review of 317 experiments found something more useful still: the longer you need to remember something, the longer the best gap between reviews. A word you need next week wants a short gap; a word you need for years wants a long one.
Cepeda, Pashler, Vul, Wixted & Rohrer (2006). Distributed practice in verbal recall tasks: a review and quantitative synthesis. Psychological Bulletin 132(3), 354–380. doi:10.1037/0033-2909.132.3.354
Cepeda, Vul, Rohrer, Wixted & Pashler (2008). Spacing effects in learning: a temporal ridgeline of optimal retention. Psychological Science 19(11), 1095–1102. doi:10.1111/j.1467-9280.2008.02209.x
How Word Gallery uses it
- Every word has its own date. There is no fixed list of reviews. Each word comes back on the day when the chance that you still remember it drops to about 90 %.
- The gaps grow. Each time you recall a word, its next gap is longer. Words you find hard come back sooner, until they stay.
- A miss is not a failure. A new word you could not say yet comes back tomorrow, then after about 3, 9 and 25 days as you keep remembering it.
- One answer a day counts. A second lesson on the same day is practice: it moves no dates.
Some words slip by tomorrow — that is normal
Forgetting a few of today's words by tomorrow is how memory works, not a sign that you did badly. Sleep is part of the schedule. In the study below, a night's sleep between two sessions halved the rounds needed to relearn the words — and six months later, more than twice as many were still remembered.
In the app, a new word that is still settling at the end of a lesson is not drilled over and over: it comes back tomorrow, after a night's sleep.
Mazza, Gerbier, Gustin, Kasikci, Koenig, Toppino & Magnin (2016). Relearn faster and retain longer: along with practice, sleep makes perfect. Psychological Science 27(10), 1321–1330. doi:10.1177/0956797616659930
The scheduler
The dates come from FSRS, an open-source spaced-repetition scheduler. It keeps two numbers for every word — how firmly you know it, and how hard it is for you — and updates both after your answers.
