Hermann Ebbinghaus

“ For ascertaining the relation of dependence between the increase in the number of repetitions of a series and the ever deeper impression of it which result, I have formulated the problem as follows: If homogeneous series are impressed to different extents as a result of different numbers of repetitions, and then 24 hours later are learned to the point of the first possible reproduction by heart, how are the resulting savings in work related to each other and to the corresponding number of former repetitions? ”

“ As the repetition of a series of 16 syllables in itself takes from 6.6 to 6.8 seconds, its after-effect 24 hours later amounts to a scant third of its own duration. In other words: 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. ”

“ In ordinary life it is of the greatest importance, as far as the form which memory assumes is concerned, whether the reproductions occur with accompanying recollection or not,—i.e., whether the recurring ideas simply return or whether a knowledge of their former existence and circumstances comes back with them. ”