Noesis Academy — effective learning techniques | noesis-academy.com
What Ebbinghaus measured between 1880 and 1885, why memory halves in days or weeks, and where the 10-20% review-timing figure comes from.
From 1880 to 1885 Hermann Ebbinghaus ran experiments on himself with nonsense syllables and published the forgetting curve in 1885 in Über das Gedächtnis. Using nonsense syllables removed meaning and prior knowledge from the equation, so the decline he measured reflected memory itself rather than familiarity with the material.
The shape he found is steep at the start and flatter later. A typical graph of the forgetting curve purports to show that humans tend to halve their memory of newly learned knowledge in a matter of days or weeks unless they consciously review the material. The first days carry the largest loss; after that, the remaining trace decays more slowly.
On narrow screens, swipe or scroll the plate sideways.
The curve is a description, not a sentence. It says what happens by default, when nothing is done. The moment review is added, the curve changes shape, which is why the same 1885 publication is the starting point for spaced repetition rather than an argument against trying.
For a single review, evidence suggests that waiting 10-20% of the time towards when the information will be needed is the optimum time. If the material is needed in ten days, a review around day one or two sits inside that window; if it is needed in a year, the first review can wait considerably longer.
The practical reading is that timing, not effort, is the adjustable variable. Reading harder does not bend the curve; reviewing at the right moment does.
Further reading