If reviewing flashcards feels like a chore, you will become averse to doing it.Tips to make your reviewing sessions more enjoyable:<ul><li>Have a diverse set of flash cards, so you don't get bored going through the same topic for a long time.</li><li>Mix in some fun cards with inspiring quotes or poems to give you short moments of relief during sessions.</li><li>Shuffle the cards to have diverse sessions.</li></ul>

Spaced repetition should be enjoyable to stick as a habit

Efficient memorization using the spacing effect: literature review of widespread applicability, tips on use & what it’s good for.

education

Learning & Education

problemsolving

Problem Solving

“If you read a piece of text through twenty times, you will not learn it by heart so easily as if you read it ten times while attempting to recite from time to time and consulting the text when your memory fails.” –<a href="https://en.wikipedia.org/wiki/Novum_Organum">The New Organon </a> , <a href="https://en.wikipedia.org/wiki/Francis_Bacon">Francis Bacon </a>

The <a href="https://en.wikipedia.org/wiki/Testing_effect">testing effect </a>is the established psychological observation that the mere act of testing someone’s memory will strengthen the memory (regardless of whether there is feedback). Since <a href="https://en.wikipedia.org/wiki/Spaced_repetition">spaced repetition </a>is just testing on particular days, we ought to establish that testing works better than regular review or study, and that it works outside of memorizing random dates in history. To cover a few papers:

<ol><li>Allen, G.A., Mahler, W.A., & Estes, W.K. (1969). <a href="https://gwern.net/doc/psychology/spaced-repetition/1969-allen.pdf">“Effects of recall tests on long-term retention of paired associates” </a>⁠. Journal of Verbal Learning and Verbal Behavior , 8, 463-470 1 test results in memories as strong a day later as studying 5 times; intervals improve retention compared to massed presentation. </li> </ol>

The research literature focuses extensively on the question of what kind of spacing is best and what this implies about memory: a spacing that has static fixed intervals or a spacing which expands? This is important for understanding memory and building models of it, and would be helpful for integrating spaced repetition into classrooms (for example, <a href="https://www.frontiersin.org/articles/10.3389/fnhum.2013.00589/full">Kelley & Whatson 2013 ’s </a>10 minutes studying / 10 minutes break schedule, repeating the same material 3 times, designed to trigger LTM formation on that block of material?) But for practical purposes, this is uninteresting; to sum it up, there are many studies pointing each way, and whatever difference in efficiency exists, is minimal. Most existing software follows SuperMemo in using an expanding spacing algorithm, so it’s not worth worrying about; as Mnemosyne developer Peter Bienstman says, it’s not clear the more complex algorithms really help⁠<a href="https://gwern.net/spaced-repetition#fn32">⁠32 </a>⁠, and the Anki developers <a href="https://faqs.ankiweb.net/what-spaced-repetition-algorithm.html">were concerned about </a>the complexity, difficulty of reimplementing SM’s proprietary algorithms, lack of substantial gains, & larger errors SM3+ risks attempting to be more optimal. So too here.

For those interested, 3 of the studies that found fixed spacings better than expanding:

<ol><li>Carpenter, S. K., & DeLosh, E. L. (2005). <a href="https://gwern.net/doc/psychology/spaced-repetition/2005-carpenter.pdf">“Application of the testing and spacing effects to name learning” </a>⁠. Applied Cognitive Psychology , 19, 619-636⁠<a href="https://gwern.net/spaced-repetition#fn33">⁠33 </a> </li><li>Logan, J. M. (2004). Spaced and expanded retrieval effects in younger and older adults . Unpublished doctoral dissertation, Washington University, St. Louis, MO This thesis is interesting inasmuch as Logan found that young adults did considerably worse with an expanding spacing after a day. </li><li>Karpicke & Roediger, 2006a </li> </ol>

The fixed vs expanding issue aside, a list of additional generic studies finding benefits to spaced vs massed:

<ul><li>Cepeda 2006 (large review used elsewhere in this page) </li><li>Karpicke & Roediger 2006a </li> </ul>

The most difficult task, beyond that of just persisting until the benefits become clear, is deciding what’s valuable enough to add in. In a 3 year period, one can expect to spend <a href="https://gwern.net/doc/www/super-memory.com/b9400b6a317f7b1d00a475362349f6eab8c9b378.html">⁠“30–40 seconds” </a>on any given item. The long run <a href="https://www.supermemo.com/en/blog/theoretical-aspects-of-spaced-repetition-in-learning">theoretical predictions </a>are a little hairier. Given a single item, the formula for daily time spent on it is Time = 1⁄500 × n thYear−1.5 + 1⁄30000. During our 20th year, we would spend t = 1⁄500 × 20−1.5 + 1⁄3000, or <code>3.557e-4 </code>minutes a day. This is the average daily time, so to recover the annual time spent, we simply multiply by 365. Suppose we were interested in how much time a flashcard would cost us over 20 years. The average daily time changes every year (the graph looks like an exponential decay, remember), so we have to run the formula for each year and sum them all; in Haskell:

Which evaluates to 1.8 minutes. (This may seem too small, but one doesn’t spend much time in the first year and the time drops off quickly⁠<a href="https://gwern.net/spaced-repetition#fn55">⁠55 </a>⁠.) <a href="https://gwern.net/doc/psychology/spaced-repetition/2012-muflax-dreamingofaworldundone.html.maff">Anki user muflax’s </a>statistics put his per-card time at 71s, for example. But maybe <a href="https://en.wikipedia.org/wiki/Piotr_Wo%C5%BAniak_(researcher)">Piotr Woźniak </a>was being optimistic or we’re bad at <a href="https://www.supermemo.com/en/blog/twenty-rules-of-formulating-knowledge">writing flashcards </a>⁠, so we’ll double it to 5 minutes. That’s our key rule of thumb that lets us decide what to learn and what to forget: if, over your lifetime, you will spend more than 5 minutes looking something up or will lose more than 5 minutes as a result of not knowing something, then it’s worthwhile to memorize it with spaced repetition. 5 minutes is the line that divides trivia from useful data.⁠<a href="https://gwern.net/spaced-repetition#fn56">⁠56 </a>(There might seem to be thousands of flashcards that meet the 5 minute rule. That’s fine. Spaced repetition can accommodate dozens of thousands of cards. See the <a href="https://gwern.net/spaced-repetition#the-workload">⁠next section </a>⁠.)

To a lesser extent, one might wonder when one is in a hurry, should one learn something with spaced repetition and with massed? How far away should the tests or deadlines be before abandoning spaced repetition? It’s hard to compare since one would need a specific regimens to compare for the crossover point, but for massed repetition, the average time after memorization at which one has a 50% chance of remembering the memorized item seems to be 3-5 days.⁠<a href="https://gwern.net/spaced-repetition#fn57">⁠57 </a>Since there would be 2 or 3 repetitions in that period, presumably one would do better than 50% in recalling an item. 5 minutes and 5 days seems like a memorable enough rule of thumb: ‘don’t use spaced repetition if you need it sooner than 5 days or it’s worth less than 5 minutes’.

I find one of the best uses for Mnemosyne is, besides the classic use of memorizing academic material such as geography or the periodic table or foreign vocabulary or Bible/​Koran verses or the avalanche of medical school facts, to add in words from <a href="https://en.wikipedia.org/wiki/Anu_Garg">A Word A Day </a>⁠<a href="https://gwern.net/spaced-repetition#fn58">⁠58 </a>and <a href="https://en.wikipedia.org/wiki/Wiktionary">Wiktionary </a>⁠, memorable quotes I see⁠<a href="https://gwern.net/spaced-repetition#fn59">⁠59 </a>⁠, personal information such as birthdays (or license plates, a problem for me before), and so on. Quotidian uses, but all valuable to me. With a diversity of flashcards, I find my daily review interesting. I get all sorts of questions - now I’m trying to see whether a Haskell fragment is syntactically correct, now I’m pronouncing Korean <a href="https://en.wikipedia.org/wiki/Hangul">hangul </a>and listening to the answer, now I’m trying to find the Ukraine on a map, now I’m enjoying some <a href="https://en.wikipedia.org/wiki/A._E._Housman">A.E. Housman </a>poetry, followed by a few quotes from <a href="https://www.lesswrong.com/">⁠LessWrong </a>quote threads, and so on. Other people use it for many other things; one application that impresses me for its simple utility is <a href="https://www.lesswrong.com/posts/YbCc3NRrr5avvWSHT/who-wants-to-start-an-important-startup?commentId=CyxaAxbokswt6ZyPh">⁠memorizing names & faces </a><a href="https://www.lesswrong.com/posts/YbCc3NRrr5avvWSHT/who-wants-to-start-an-important-startup?commentId=RC2TbuNbD9sXTiH9e">⁠of </a><a href="https://www.lesswrong.com/posts/YbCc3NRrr5avvWSHT/who-wants-to-start-an-important-startup?commentId=qPQGQd6E3hZ5DsLz4">⁠students </a>although <a href="https://gwern.net/doc/psychology/spaced-repetition/2012-chessdata-perfectpitchspacedrepetition.webm">⁠learning musical notes </a>is also not bad.

On average, when I’m studying a new topic, I’ll add 3-20 questions a day. Combined with my particular memory, I usually review about 90 or 100 items a day (out of the total >18,300). This takes under 20 minutes, which is not too bad. (I expect the time is expanded a bit by the fact that early on, my formatting guidelines were still being developed, and I hadn’t the full panoply of categories I do now - so every so often I must stop and edit categories.)

If I haven’t been studying something recently, the exponential decaying of reviews slowly drops the daily review. For example, in March 2011, I wasn’t studying many things, so for 2011-03-24–2011-03-26, my scheduled daily reviews are 73, 83, and 74; after that, it’ll probably drop down into the 60s, and then after another week or two, into the 50s and so on until it hits the minimum plateau which will slowly shrink over years. (I haven’t gone long enough without dumping cards in to know what that might be.) By February 2012, the daily reviews are in the 40s or sometimes 50s for similar reasons, but the gradual shrinkage will continue. We can see this vividly, and we can even see a sort of analogue of the original forgetting curve, if we ask Mnemosyne 2.0 to graph the number of cards to review per day for the next year up to February 2013 (assuming no additions or missed reviews etc.):

If Mnemosyne weren’t using spaced repetition, it would be hard to keep up with 18,300+ flashcards. But because it is using spaced repetition, keeping up is easy.

Nor is 18.3k extraordinary. Many users have decks in the 6-7k range, Mnemosyne developer <a href="https://groups.google.com/g/mnemosyne-proj-users/c/QzhysVWtdFE">Peter Bienstman </a>has >8.5k & Patrick Kenny >27k, <a href="https://groups.google.com/g/mnemosyne-proj-users/c/7_RPX9sdc4s">Hugh Chen </a>has a 73k+ deck, and in <a>#anki </a>⁠, they tell me of one user who triggered bugs with his >200k deck. 200,000 may be a bit much, but for regular humans, some amount smaller seems possible - it’s interesting to compare SRS decks to the feat of <a href="https://gwern.net/doc/psychology/spaced-repetition/2010-seamon.pdf">memorizing Paradise Lost </a>or to the Muslim title of <a href="https://en.wikipedia.org/wiki/Hafiz_(Quran)">‘hafiz’ </a>⁠, one who has memorized the ~80,000 words of the Koran, or the stricter ‘hafid’, one who had memorized the Koran and 100,000 <a href="https://en.wikipedia.org/wiki/Hadith">hadiths </a>as well. Other forms of memory are still more powerful.⁠<a href="https://gwern.net/spaced-repetition#fn60">⁠60 </a>(I suspect that spaced repetition is involved in one of the few well-documented cases of “<a href="https://en.wikipedia.org/wiki/Hyperthymesia">hyperthymesia </a>”, <a href="https://en.wikipedia.org/wiki/Jill_Price">Jill Price </a>: reading <a href="https://web.archive.org/web/20131208072327/https://www.wired.com/medtech/health/magazine/17-04/ff_perfectmemory?currentPage=all">⁠Wired </a>⁠, she has ordinary fallible powers of memorization for surprise demands with no observed anatomical differences and is restricted to “her own personal history and certain categories like television and airplane crashes”; further, she is a packrat with obsessive-compulsive traits who keeps >50,000 pages of detailed diaries perhaps due to a childhood trauma & associates daily events nigh-involuntarily with past events. Marcus says the other instances of hyperthymesia resemble Price.)

When should one review? In the morning? In the evening? Any old time? The studies demonstrating the spacing effect do not control or vary the time of day, so in one sense, the answer is: it doesn’t matter - if it did matter, there would be considerable variance in how effective the effect is based on when a particular study had its subjects do their reviews.

So one reviews at whatever time is convenient. Convenience makes one more likely to stick with it, and sticking with it overpowers any temporary improvement.

If one is not satisfied with that answer, then on general considerations, one ought to review before bedtime & sleep. <a href="https://en.wikipedia.org/wiki/Memory_consolidation#Spacing_effect">Memory consolidation </a>seems to be related, and <a href="https://en.wikipedia.org/wiki/Sleep_and_memory">sleep </a>is known to powerfully influence what memories enter long-term memory, <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0033079">strengthening memories </a>of material learned close to bedtime and <a href="https://www.pnas.org/doi/full/10.1073/pnas.0900271106">increasing creativity </a>⁠; interrupting sleep without affecting total sleep time or quality still <a href="https://www.pnas.org/doi/10.1073/pnas.1015633108">damages memory formation in mice </a>⁠<a href="https://gwern.net/spaced-repetition#fn61">⁠61 </a>⁠. So reviewing before bedtime would be best. (Other mental exercises show improvement when trained before bedtime; for example, <a href="https://gwern.net/dnb-faq#sleep">⁠dual n -back </a> .) One possible mechanism is that it may be that the <a href="https://www.jneurosci.org/content/31/5/1563.full">expectancy </a>of future reviews/​tests is enough to encourage memory consolidation during sleep; so if one reviews and goes to bed, presumably the expectancy is stronger than if one reviewed at breakfast and had an eventful day and forgot entirely about the reviewed flashcards. (See also the correlation between time of studying & GPA in Hartwig & Dunlosky 2012 .) Neural growth may be related; from Stahl 2010 :

Recent advances in our understanding of the neurobiology underlying normal human memory formation have revealed that learning is not an event, but rather a process that unfolds over time.<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1876761/">16 </a>⁠,<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3650827/">17 </a>⁠,<a href="https://gwern.net/doc/psychology/spaced-repetition/2010-oneill.pdf">18 </a>,[Squire 2003   <a href="https://www.amazon.com/Fundamental-Neuroscience-Second-Larry-Squire/dp/0126603030/?tag=gwernnet-20">Fundamental Neuroscience </a> ],<a href="https://gwern.net/doc/www/davidjf.free.fr/12f68acf6714e8d2200c12fddf7b1b1241fc1f82.pdf">20 </a> Thus, it is not surprising that learning strategies that repeat materials over time enhance their retention.20,<a href="https://gwern.net/doc/psychology/spaced-repetition/1980-glenberg.pdf">21 </a>⁠,<a href="https://gwern.net/doc/psychology/spaced-repetition/1991-toppino.pdf">22 </a>⁠,<a href="https://gwern.net/doc/psychology/spaced-repetition/1978-landauer.pdf">23 </a>⁠,<a href="https://gwern.net/doc/www/www.wsu.edu/992e041a4a60ef70f816fadb6ac3ecc7409ba6c1.html">⁠24 </a>⁠,<a href="https://pdfs.semanticscholar.org/6698/bf91c9333faa0d333a800254b8063230d4f4.pdf">25 </a>⁠,<a href="https://gwern.net/doc/psychology/spaced-repetition/2007-pashler.pdf">26 </a>

…Thousands of new cells are generated in this region every day, although many of these cells die within weeks of their creation.<a href="https://pdfs.semanticscholar.org/45c2/7c08fbb43f8728e69a7447366d4a4f74e088.pdf">⁠31 </a> The survival of dentate gyrus neurons has been shown to be enhanced in animals when they are placed into learning situations.16-20 Animals that learn well retain more dentate gyrus neurons than do animals that do not learn well. Furthermore, 2 weeks after testing, animals trained in discrete spaced intervals over a period of time, rather than in a single presentation or a ‘massed trial’ of the same information, remember better.16-20 The precise mechanism that links neuronal survival with learning has not yet been identified. One theory is that the hippocampal neurons that preferentially survive are the ones that are somehow activated during the learning process.16-20 ⁠<a href="https://gwern.net/spaced-repetition#fn62">⁠62 </a>The distribution of learning over a period of time may be more effective in encouraging neuronal survival by allowing more time for changes in gene expression and protein synthesis that extend the life of neurons that are engaged in the learning process.

…Transferring memory from the encoding stage, which occurs during alert wakefulness, into consolidation must thus occur at a time when interference from ongoing new memory formation is reduced.17,18 One such time for this transfer is during sleep, especially during non-rapid eye movement sleep, when the hippocampus can communicate with other brain areas without interference from new experiences.<a href="https://pdfs.semanticscholar.org/d0a7/f06ed267f3193daab1175a65abb7a067bef4.pdf">⁠32 </a>⁠,<a href="https://pdfs.semanticscholar.org/77fd/0cf03de8a6c4f56c5decc7c47ebe69cf98c1.pdf">⁠33 </a>⁠,<a href="https://gwern.net/doc/psychology/spaced-repetition/2001-maquet.pdf">34 </a> Maybe that is why some decisions are better made after a good night’s rest and also why pulling an all-nighter, studying with sleep deprivation, may allow you to pass an exam an hour later but not remember the material a day later.

Spaced Repetition for Efficient Learning

Spaced repetition should be enjoyable to stick as a habit

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