Copyright © 1999 Massachusetts Institute of Technology
Hermann Ebbinghaus (1850-1909) was the first psychologist to apply experimental methods to the study of human MEMORY. His groundbreaking book summarizing his experimental work, Über das Gedächtnis, was published in 1885. The English translation appeared in 1913 as Memory: A Contribution to Experimental Psychology and is still in print and well worth reading today.
Ebbinghaus was born in Barmen, Germany, studied at the University of Bonn, and began his pioneering research on memory in Berlin in 1878. His work is notable for its many original features. In addition to performing the first experiments on memory, he provided an authoritative review of probability and statistics, an elegant command of experimental design, a mathematical model of the forgetting function, an enlightened discussion of problems of experimenter bias and demand characteristics in research, and a set of experimental results that has stood the test of time. All the experiments reported by Ebbinghaus have been replicated.
No one knows how he created his ingenious methods, although historians have speculated that his purchase of a copy of Fechner's book (in English) (1860/1966) and his reading about psychophysical methods may have been the source of his own clever methodology (see PSYCHOPHYSICS). Ebbinghaus solved the three problems faced by all cognitive/experimental psychologists in their work: to convert unobservable mental processes into observable behavior; to measure the behavior reliably; and to show how the behavior is systematically affected by relevant factors and conditions.
Ebbinghaus solved these problems by creating long lists of nonsense syllables (ZOK, VAM , etc.) to be memorized. He hoped that using these materials would permit him to study formation of new associations with relatively homogeneous materials. He learned the lists by reciting them in time to a metronome and measuring the amount of time or the number of repetitions taken until he could recite a list perfectly. He discovered quickly that the longer the list, the more repetitions were required to effect a perfect recitation. Although this was hardly a surprising finding, Ebbinghaus plotted the exact relation between the length of the series and the amount of time (or number of repetitions) to recall it once perfectly, a measure known as trials to criterion. He then had to determine how to measure retention of the series at some later point in time. Ebbinghaus's clever idea was to have himself relearn the list to the same criterion (of one perfect recitation); he could then obtain the savings (in time or repetitions) in relearning the series and use it as his measure of list retention. The greater the savings (the fewer trials to relearn the series), the greater is retention; conversely, if the same number of trials is needed to relearn the series as was originally required to learn it, then its forgetting was complete.
The beauty of Ebbinghaus's relearning and savings method is that measures of retention could be obtained even when recall of the list items was absent. This is one reason Ebbinghaus preferred his objective savings technique over what he called introspective techniques, such as recall or recognition. In a sense, ten years before FREUD proposed his ideas of unconscious mentation, Ebbinghaus had already devised a method whereby they could be studied. Even if someone failed to bring information to mind consciously, the unconscious residue could be examined through his relearning and savings technique.
Ebbinghaus made many discoveries with his new methods. He obtained a relatively precise relation between number of repetitions and forgetting: For every three repetitions of a list, he saved one repetition in relearning it a week later. He also discovered the logarithmic nature of the forgetting function; great forgetting occurred soon after learning, with the rate of forgetting slowing over time. In addition, he fitted an equation to the forgetting function. He also discovered the advantage of spaced repetitions of lists to massed repetition, when he found that "38 repetitions, distributed in a certain way over the three preceding days, has just as favorable an effect as 68 repetitions made on the day just previous" (page 89).
Ebbinghaus asked the question of whether associations were only formed directly, between adjacent nonsense syllables, or whether in addition remote associations were formed between syllables that were not adjacent. Using the symbols A, B, C, D, E, F, G, and H to represent syllables in a list to be learned, he asked whether there are only associations between A and B, B and C, and so on, or whether there are also associations (albeit presumably weaker ones) between A and C, A and D, and so on. Ebbinghaus developed a clever transfer of training design to answer the question. He derived lists for relearning that had associations of varying remoteness, which can be symbolized as ACEG . . . BDFH (for one degree of remoteness) or ADG . . . BEH . . . CF for two degrees of remoteness, and so on. He discovered that he did show savings in relearning these derived lists relative to control lists (that had no associations), and he concluded that the savings were the result of remote associations. In reviewing Ebbinghaus's work, William JAMES (1890) noted that "Dr. Ebbinghaus's attempt is as successful as it is original, in bringing two views, which seem at first sight inaccessible to proof, to a direct and practical test, and giving the victory to one of them" (page 677). The derived list experiments might be the first case of competitive hypothesis testing between two theories in experimental psychology.
Ebbinghaus was the only subject in all of his experiments, and this fact might give rise to doubt about the results. But he was a meticulous scientist, employing LOGIC, controls, and precise techniques far ahead of this time. All his results have stood the test of time. His particular methods of studying memory were rather quickly supplanted by other techniques -- the introspective techniques of recall and recognition that he had wished to avoid -- but his great achievements live on. He was the pioneer in showing how complex and unconscious mental processes could be studied through objective means by careful, systematic observation. As such, he helped pave the way for modern cognitive/experimental psychology.
Ebbinghaus, H. (1964). Memory: A Contribution to Experimental Psychology. Trans. H. A. Ruber and C. E. Bussenius. New York: Dover. Original work published 1885.
Fechner, G. (1860/1966). Elements of Psychophysics. Vol. 1. H. E. Adler, D. H. Howes, and E. G. Boring, Eds. and Trans. New York: Holt, Rinehart, and Winston.
James, W. (1890). Principles of Psychology. New York: Holt.
Postman, L. (1968). Hermann Ebbinghaus. American Psychologist 23:149-157.
Roediger, H. L. (1985). Remembering Ebbinghaus. Contemporary Psychology 30:519-523.
Tulving, E. (1992). Ebbinghaus, Hermann. In L. R. Squire, Ed., Encyclopedia of Learning and Memory. New York: Macmillan.
Copyright © 1999 Massachusetts Institute of Technology