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 and repetition scheduling.

Spaced repetition originates from the way memory works. Initially, we need to make an early review of the learning material, to make sure it is retained in memory. However, as the material gradually gets consolidated, the review may be less and less frequent.

Most advanced applications of spaced repetition make use of 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.

Surprisingly, 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.

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

The Pimsleur language learning system uses spaced repetition techniques.

Prominent researchers

• Cecil Alec Mace
• Hermann Ebbinghaus
• Sebastian Leitner
• Piotr Wozniak

Computer software using spaced repetition

Free software/Open source (FOSS)

• jMemorize An open-source Java program using the famous Leitner system. Released under the GPL.
• Pauker (Pauker) Java program, released under the GPL.
• MemAid Similar to SuperMemo, but using a neural network, released under the GPL. No longer under active development.
• The Mnemosyne Project Heir to MemAid, released under the GPL.
• Memorize Word An open-source Java program using the Leitner system in fully multimedia manners.
• Rememorizer A flashcard program that aids in extremely efficient memorization. Cross platform, GPL.
• Granule C++ POSIX program, released under the GPL. There is also a Nokia 770 , and Windows versions available.
• Gradint a program for self-study of foreign languages (GPL; cross-platform; requires data to be added)

Commercial software

• 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.
• Genius A freeware flashcard program for Mac Os X (10.3 and up). Performs fuzzy answer checking and highlights errors.
• SuperMemo ^* A freeware and commercial program that uses spaced repetition.
• VTrain (Vocabulary Trainer) A spaced-learning system with a scheduling facility. Shareware.
• MindBrainer A commercial spaced-learning system for the Pocket PC using 'Graduated Interval Recall' in training and spaced repetition in testing.
• Fullrecall uses artificial neural network, which gradually grasp personal memory model

Memory

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