January 24, 1850 (a Thursday)

Hermann Ebbinghaus

On this date, the German psychologist Hermann Ebbinghaus was born.

The scientific study of memory started with the work of Hermann Ebbinghaus, published in 1885 in the book Memory: A Contribution to Experimental Psychology. He was a careful, cautious researcher who followed simple but logical procedures.

Ebbinghaus devised a set of items to be committed to memory that would have no previous associations, the so-called nonsense syllables. These each consist of two consonants separated by a vowel (C-V-C) that does not spell anything in one’s language — in English, BAF would be an example. Ebbinghaus constructed 2,300 of these items and then proceeded to memorize them in lists of about 20. He learned each list of these syllables until he had reached a pre-established criterion (perfect recall), and then recorded how many he was able to retain after specific time intervals. He also noted how many trials were necessary for relearning after the syllables had been forgotten. His first set of trials took place over the course of one year (1879-1880) and he replicated the experiments three years later.

The curved brown and dotted lines represent forgetting curves; the green line represents the learning curve. Relearning at periodic intervals produces forgetting curves that are progressively flatter.

Ebbinghaus made several findings that are still relevant and supported to this day. First, arguably his most famous finding, the forgetting curve. The forgetting curve refers to the exponential curve that describes how fast we tend to forget information after we have learned it. The sharpest decline is in the first twenty minutes, then in the first hour, and then the curve evens off after about one day.

The learning curve, which was described by Ebbinghaus, refers to the curve that describes how fast we relearn information. The sharpest increase occurs after the first relearning (“repetition”), and gradually evens out, meaning that less and less new information is retained with each successive relearning. Like the forgetting curve, the learning curve is also exponential.

The Ebbinghaus Illusion. Note that the orange circles appear of different sizes, even though equal.

Interestingly, Ebbinghaus is also credited with discovering an optical illusion now known after its discoverer — the Ebbinghaus illusion, which is an illusion of relative size perception. In the best-known version of this illusion, two circles of identical size are placed near to each other and one is surrounded by large circles while the other is surrounded by small circles; the first central circle then appears smaller than the second central circle. This illusion is now used extensively in research in cognitive psychology, to find out more about the various perception pathways in our brain.


  • Plucker, J. A. (Ed.). (2003). “Human intelligence: Historical influences, current controversies, teaching resources”. Retrieved 24 Jan 2012 from http://www.indiana.edu/~intell

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