Spaced repetition

Spaced repetition is a learning technique in which increasing intervals of time are used between subsequent reviews. Alternative names include expanding rehearsal, graduated intervals, repetition spacing, repetition scheduling, spaced retrieval and expanded retrieval. Spaced repetition is not simple rote repetition of phrases. It emphasizes active recall rather than recognition, and uses recall methods of memory such as questioning, free recall, free association, intellective reflection, or prompting using other mnemonic triggers or cues.

Humans differ little in the way their memory works. People with large differences in IQ will often exhibit similar spaced repetition patterns. For example, when we learn a foreign word, most people require a repetition within 1-10 days to ensure 95% retention. The second repetition may already come later. For example, between 2-25 days. After a few repetitions, well structured and meaningful learning material can be repeated with intervals lasting many years.

Applications
Practical applications of spaced repetition were first suggested in the book Psychology of Study by Prof. C. A. Mace in 1932.

Pimsleur language courses use spaced repetition techniques, and in the 1970s Sebastian Leitner devised his Leitner system, an all-purpose system based on flashcards.

More recently, spaced repetition has also been implemented into computer-assisted language learning software. Such software can collect information about student's memory and gradually adapt the optimum spacing of repetitions to individual needs. A typical optimization criterion used in spaced repetition is the requested level of knowledge retention, i.e. percent of knowledge that is to be remembered.

There are several families of algorithms for scheduling spaced repetition:
 * Neural networks based
 * Sebastian Leitner system earning machines:
 * 5 stages
 * n stages
 * SM-family of algorithms (SuperMemo):
 * SM-0
 * SM-2
 * SM-4
 * SM-5
 * SM-6
 * SM-8
 * SM-11

Prominent researchers

 * Cecil Alec Mace
 * Hermann Ebbinghaus
 * Sebastian Leitner
 * Piotr Wozniak (creator of SuperMemo)

Free software/Open source (FOSS)

 * Anki Supports Windows, OS X, Linux, web & cell phone reviews. Any material is supported, but special features are included for Japanese. Released under the GPL.
 * Gradint a cross-platform spaced-repetition system for oral second-language practice, released under the GPL
 * Granule a free Open source space-repetition system. Works under Linux, Nokia 770, Windows, and GPE Palmtop Environment (handhelds). Released under the GPL.
 * jMemorize An open-source Java program using the Leitner system. Released under the GPL.
 * KhatzuMemo Web-based program. Free to use. Unicode-enabled so works with multiple languages. Accessible from both PC and mobile web browsers.
 * MemAid Similar to SuperMemo, but using a neural network, released under the GPL. No longer under active development.
 * Memorize Word An open-source Java program using the Leitner system in fully multimedia manners. Q Public License (QPL).
 * The Mnemosyne Project Heir to MemAid, released under the GPL.
 * Pauker Java program using the Leitner system. Released under the GPL.
 * Rememorizer A flashcard program that aids in extremely efficient memorization. Cross platform, GPL.
 * Twinkle Open-source program to memorize foreign words with flash cards on PalmOS. Supports foreign fonts.  Released under the GPL.
 * OpenCards A free flashcard learning extension for OpenOffice.org Impress. Released under BSD license.
 * toMOTko A free (GPL) flashcard program to learn foreign vocabulary for the Zaurus.
 * Rememberize A Web 2.0 application for creating online flashcards with a Leitner-style learning schedule.
 * Fresh Memory A cross-platform utility for learning foreign words with flashcards. Written with C++, uses QT library for its GUI. Available for Linux, Windows, MacOS. License: GPL 2

Commercial software

 * BYKI Flash-card style learning with pronunciation in 41 languages using proprietary "order-of-presentation" algorithm which aims for a "perfect recall" objective. Freeware.
 * BYKI Deluxe Non-free version of BYKI (above), which includes authoring and extra activities.
 * cueFlash.com
 * Declan Software - Audio Flashcards Audio flashcards software for Japanese, Chinese, Korean, Russian, Arabic, Russian, German, French, Italian & Indonesian. Shareware
 * Flashcard 101 Flashcard Software for your PC and Pocket PC
 * Flash Card Manager Easy-to-use, optimizes your study time. Windows and Pocket PC
 * Fullrecall uses artificial neural network, which gradually grasps personal memory model
 * Genius A freeware flashcard program for Mac OS X (10.3 and up). Performs fuzzy answer checking and highlights errors.
 * MemoryLifter A freeware flashcard program for Windows. Excellent features such as image, sound, and video support on flashcards.  Unicode support.  "Correct on the fly" forces correct answers and highlights incorrect spellings.
 * Mental Case Commercial application for Mac OS X. Combines flash cards with repetitive learning, and quick data entry. Supports text and images, including built-in screen shot functionality and web-cam (iSight) capture. Flash card presentations are beautifully presented with themes and attractive transitions.
 * MindBrainer A commercial spaced-learning system for the Pocket PC using 'Graduated Interval Recall' in training and spaced repetition in testing.
 * ProProfs Educational flash card maker
 * RecallPlus A 3d Diagrammatic Mapping tool which also tests 'FlashCard' style using spacing effect. This concept mapping hybrid is aimed at students trying to optimize learning/study time use. Won 2005-6 Esc 'peoples choice' award.
 * Studycard Studio A multimedia flashcard application with spaced repetition for Mac OS and Palm OS.
 * SuperMemo A freeware and commercial program that uses spaced repetition.
 * StudyMachine.org Create, share, study, search, & print flashcards for free online.
 * studyPerfect Flashcard Software
 * StudyTag A new free web application that uses spaced repetition and active recall.
 * Quizlet online flash card software
 * Viaverbi A new shareware flashcard based language learning program for Mac OS X. Uses a promising a spaced repetition algorithm.
 * Vocabulary Assistant - Learn foreign vocabulary on your mobile phone.
 * Vocabulary Trainer - Memorize foreign language vocabulary permanently.
 * VTrain (Vocabulary Trainer) A spaced-learning system used in 40 universities. Shareware.
 * Winflash (Winflash) Award-winning system with Leitner and several other proprietary learning modes. Use PDA, iPod or your regular computer or laptop.
 * Teach2000 Freeware Windows program to memorize a foreign language. Unicode enabled.

Lists of flashcard software

 * List of flashcard sites and programs
 * Memorization Software Reviewed