Algorithms for Life: Spaced Repetition — Sources

[R01] Ebbinghaus, H. (1885). Über das Gedächtnis — foundational memory experiments establishing the forgetting curve and spacing effect.
[R02] Cepeda, N. J., Vul, E., Rohrer, D., Wixted, J. T., & Pashler, H. (2008). Spacing effects in learning: A temporal ridgeline of optimal retention. Meta-analysis of 317 experiments, 839 assessments, N=1,350+.
[R03] Claude synthesis (2025). Comprehensive research synthesis on spaced repetition systems — integrating SLA literature, platform analytics, polyglot testimony, and implementation science.
[R04] Dempster, F. N. (1988). The Spacing Effect: A Case Study in the Failure to Apply the Results of Psychological Research. American Psychologist, 43(8), 627–634.
[R05] BrainFacts.org (2021). The Neuroscience Behind the Spacing Effect — review of CREB mechanisms in Drosophila and mammalian models.
[R06] Smolen, P., Zhang, Y., & Bhatt, D. K. (2016). The right time to learn: Mechanisms and optimization of spaced learning. Nature Reviews Neuroscience. PMC5126970 — MAPK temporal dynamics and synaptic plasticity.
[R07] Wang, J. et al. (2025). Spaced learning induces neural integration in default mode network subsystems. Communications Biology. Nature. — fMRI evidence for hippocampal-cortical consolidation differences.
[R08] Woźniak, P. (2025). The True History of Spaced Repetition. SuperMemo.com — historical account of SM-0 through SM-18 algorithm development.
[R09] SuperMemo (2025). SuperMemo Algorithm documentation. help.supermemo.org — technical specification of SM-2 through SM-18.
[R10] Anki Forums / Reddit (March 2025). FSRS-5 community adoption discussions, settings optimization, and user sentiment.
[R11] Ye, J. et al. (2025). FSRS algorithm specification — 21-parameter model benchmarked across 727M reviews from ~10K Anki users. open-spaced-repetition GitHub.
[R12] Kim, S. K. & Webb, S. (2022). Meta-analysis of spaced practice in vocabulary learning — 48 experiments, N=3,411, effect sizes g=1.04–2.34.
[R13] González-Fernández, B. (2025). Recognition precedes recall across vocabulary components — N=314 EFL learners, developmental sequence study.
[R14] Stewart, J. et al. (2024). Lexical recall and recognition as distinct psychometric constructs — theoretical and empirical argument.
[R15] Duolingo company metrics (2024–2025). 500M+ users, 103.6M MAU, ~2% paid conversion, 7-day streak engagement data — investor reports and product announcements.
[R16] Systematic review of Duolingo effectiveness (2021). Taylor & Francis — critical assessment of design decisions, gamification limitations, and evidence gaps.
[R17] Anki Forums — Collection of Anki Resources thread (2025). AnkiAIUtils, custom schedulers, template ecosystem, AI card generation discussions. forums.ankiweb.net.
[R18] Grok synthesis (2025). Real-time survey of SRS app ecosystem — Duolingo AI features, Memrise updates, Taalhammer/Memozora entrants, community sentiment from X/Reddit.
[R19] Kornell, N. & Bjork, R. A. (2008). Learning concepts and categories: Is spacing the enemy of induction? Psychological Science — 83% metacognitive preference for massed practice.
[R20] Hendrick, C. (2025). What Makes Spaced Practice So Powerful? — synthesis of working memory depletion and mental rehearsal evidence in spaced learning.
[R21] Polyglot practitioner testimony — Steve Kaufmann (LingQ, 20+ languages), Luca Lampariello (20 languages), Gabriel Wyner (Fluent Forever). Compiled from interviews, published methods, and community posts.
[R22] American Board of Family Medicine (2024). Spaced repetition in continuing medical education — N=26,258 physicians, d=0.62 for learning advantage. PubMed 39250798.