The Curve of Forgetting

An excerpt from the beginning of CHAPTER I - Historical Survey, THE problems that present themselves in connection with the topic of forgetting are (1) the rate at which forgetting progresses, (2) the form of the curve showing the relation of forgetting to the lapse of time, and (3) whether there are any constant relations between either the rate of forgetting or the shape of this curve, on the one hand, and, on the other, the kinds of subject matter or the kinds of reagents, or the amount or manner of the practise or learning. The first application of modern scientific methods in the study of memory and of forgetting was the work of Ebbinghaus, which he published in 1885. Ebbinghaus assumed that when experience has weakened in its susceptibility to recall the remaining association strength can be measured best by the number of repetitions that it saves in relearning. Another person served him as subject in preliminary experiments; but in the principal experiments Ebbinghaus acted both as experimenter and subject. As he admits, his results are, therefore, of much less value especially for general psychology. The material learned in the experiments in forgetting consisted of 163 series, each containing 13 nonsense syllables. Every syllable contained a consonant, a vowel and then another consonant. Ebbinghaus took especial pains to avoid any succession of letters or of syllables that might suggest devices in learning. He read a series and then recalled as many syllables as possible until he reproduced the whole series once without an error. Whenever a series could not be promptly recalled in its entirety he read the remainder from the paper. The rate was kept constant at 150 syllables per minute by means of a metronome. Seven of the series were memorized one day and one was relearned at each of seven intervals of various lengths. The data of the shorter periods were the average results of from 12 to 16 series, and those of the larger intervals of from 22 to 26 series. The results of this investigation of Ebbinghaus I present in the form of a table of arrays and a table of central tendencies and measures of variability. It can be seen that the portions of the work that were necessary to be performed again were approximately, after 20 minutes 1/3, after 1 hour 1/2, after 9 hours 2/3-, after 24 hours 2/3 +, after 6 days 3/4, and after 31 days 4/5. His statement of his conclusions from these results is, "The ratio of what is retained to what is forgotten varies inversely as the logarithm of the time.'' Besides being the first experimental research in this group of phenomena, this was the first very extended laboratory investigation of the mental processes that are not closely paralleled by definite, commensurate, physical stimuli. In addition to this, all who have carried on experimental investigations in memory, and most especially in forgetting, will agree that the task as it was performed by Ebbinghaus required closeness of application and patient persistence that was nothing less than heroic. However, the fact that his work has more than one claim to a place among pioneer achievements is sufficient excuse for several imperfections in his methods.