Forgetting curve
The pattern describing how memory retention declines over time after learning. First measured experimentally by German psychologist Hermann Ebbinghaus, who tested himself by memorizing lists of nonsensical syllables and timing his own recall (Ebbinghaus, Über das Gedächtnis, 1885; translated as Memory: A Contribution to Experimental Psychology, 1913).
The original findings
Per The Gamer’s Brain (book) (Chapter 4): Ebbinghaus’s results were stark — after only 20 minutes, about 40% of memorized content was already forgotten, and after a day, nearly 70% was gone. Hodent frames this as the worst-case scenario: it describes forgetting of non-meaningful content learned with no mnemonic technique and no real purpose. When material is meaningful, and when the learning environment reinforces it (repetition across different contexts, increased depth of processing), the rate of forgetting is significantly reduced.
The spacing effect
The forgetting curve becomes progressively less steep each time information is repeated — which is the basis of the spacing effect: distributing repetition over time consolidates learning more effectively than massing it all at once. Hodent cites this literature (Paivio 1974; Toppino et al. 1991; and Greene, “Repetition and Spacing Effects,” 2008, in Learning and Memory: A Comprehensive Reference) directly when recommending that game tutorials distribute teaching over time rather than front-loading it — introducing one mechanic, reinforcing it through repeated use, then layering in a second mechanic while the first keeps consolidating (her Super Mario Bros. jump-then-shoot example).
Why it matters for games
Hodent applies the forgetting curve to a very concrete game-design problem: when a player quits a session and returns later — after an unknown gap of hours or days — some of what they learned in the previous session has been lost, and the game typically doesn’t account for this gap. This can create a real mismatch between the game’s difficulty (calibrated to where the player’s skill left off) and the player’s actual current skill (degraded by forgetting). Her recommended mitigations: give reminders when a player resumes (Alan Wake’s “previously on” story recap), or design the HUD to persistently display information a player would otherwise have to recall from memory (Assassin’s Creed Syndicate’s always-visible control mapping) — reducing reliance on memory retrieval altogether rather than fighting the forgetting curve directly.
Related
- Working memory — what fails to consolidate from working memory into long-term memory is what the forgetting curve describes
- Onboarding flow — the practical surface where spaced, distributed teaching is applied