Hermann Ebbinghaus, answered from the texts and cited to the page.
The method began with a problem of material. Ordinary words and verses carry too much prior association — one passage is easy because it is familiar, another hard because it is strange, and the difference tells you nothing about memory as such. So I constructed a material as nearly uniform and meaningless as I could manage: syllables of the form consonant-vowel-consonant, drawn from the simple consonants of the alphabet and eleven vowel sounds, yielding some 2,300 distinct units in all.1
These were mixed, drawn by chance, and assembled into series of varying lengths to serve as the stuff of each experiment.2 The aim at each sitting was to read a series aloud, attentively, until I could just reproduce it from memory — no more.3 Then came the critical measure. Rather than asking simply whether I could recall a series after a day or a week, I asked how much work relearning cost compared with learning from scratch.
The difference — the repetitions saved — is what I called the savings, and it is a far more sensitive instrument than recall alone, because it catches retention that has sunk below the threshold of conscious recollection but has not vanished entirely. What the numbers showed was orderly. The more repetitions invested in the first learning, the less work relearning required twenty-four hours later, and the relation held with remarkable regularity: for each three additional repetitions spent on a given day, I saved approximately one repetition the following day.4
Further, when a series was learned on several successive days, the savings between consecutive days formed something close to a decreasing geometrical progression — the gains from each additional day of practice diminishing in a lawful, predictable way.5 Memory, approached this way, is not capricious. It submits to number, and the numbers yield law.
Out of the simple consonants of the alphabet and our eleven vowels and diphthongs all possible syllables of a certain sort were constructed, a vowel sound being placed between two consonants. These syllables, about 2,300 in number, were mixed together and then drawn out by chance and used to construct series of different lengths.Memory A Contribution to Experimental Psychology
These syllables, about 2,300 in number, were mixed together and then drawn out by chance and used to construct series of different lengths, several of which each time formed the material for a test.Memory A Contribution to Experimental Psychology
the separate series — each for itself — were first read attentively a given number of times (after frequently repeated readings they were recited by heart instead of read), and that 24 hours later I relearned up to the point of first possible reproduction the series thus impressed and then in part forgotten.Memory A Contribution to Experimental Psychology
for each three additional repetitions which I spent on a given day on the study of a series, I saved, in learning that series 24 hours later, on the average, approximately one repetition; and, within the limits stated, it did not matter how many repetitions altogether were spent on the memorisation of a series.Memory A Contribution to Experimental Psychology
If series of nonsense syllables or verses of a poem are on several successive days each time learned by heart to the point of the first possible reproduction, the successive differences in the repetitions necessary for this form approximately a decreasing geometrical progression.Memory A Contribution to Experimental Psychology