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The first 80 years of research on memory is a story of changing assumptions about the nature of memory. The earliest researchers, such as Ebbinghaus, assumed that memory was a process of receiving experiences and storing them away to be recalled later. Gradually the picture grew more complicated. By the 1960s, researchers were documenting complex encoding processes that transformed information as it was taken into memory. In this section of the chapter, we will start with early memory research and examine how assumptions changed over time.

  Hermann Ebbinghaus

The scientific study of memory started with the work of Hermann Ebbinghaus, published in 1885 in the book Memory: A Contribution to Experimental Psychology. Ebbinghaus was a careful, cautious researcher who followed simple but logical procedures. He presented himself with items to memorize, waited for a precise amount of time, and then tested himself to see how much he remembered. This basic procedure is still used in most research on memory.

Why did Ebbinghaus use nonsense syllables?

Ebbinghaus tested himself with nonsense syllables : letter combinations like RIY and TPR that were supposedly meaningless. He rejected the idea of using prose (ordinary writing) or poetry, because people would have too many associations to the material, and that might affect their memory. As Ebbinghaus put it:

These materials [poetry and prose] bring into play a multiplicity of influences that change without regularity and are therefore disturbing. Such are associations which dart here and there, different degrees of interest, lines of verse recalled because of their striking beauty, and the like. All this is avoided with our syllables. (Ebbinghaus 1885/1913, p.23)

Ebbinghaus used nonsense syllables because they were stimuli nobody had seen before, and he wanted to study material being learned for the first time. As it turns out, the syllables are not treated as "nonsense" by most people who try to memorize them. Subjects easily relate nonsense syllables to actual or made-up words. However, that realization came decades after Ebbinghaus started his research.

What are different types of trigrams?

Nonsense syllables are non-word letter combinations. A nonsense syllable composed of three consonants is a CCC trigram. One with a consonant, vowel, and consonant is a CVC trigram. A two-letter nonsense syllable is a bigram; a four-letter syllable is a quadragram.

CCC trigrams                                CVC trigrams


Who was Ebbinghaus's main subject? What is a "trial" in memory research?

Ebbinghaus worked primarily with one subject: himself. During his experiments, he memorized over 2,000 nonsense syllables. He called each presentation of nonsense syllables a trial. Ebbinghaus gave himself repeated trials until he learned the material to a criterion level of memorization. In his case, the criterion was two perfect (error-free) recalls of the list.

A criterion is a goal or standard that must be met, in order for memorization to be considered complete. Why did Ebbinghaus use the criterion of two perfect recalls of the list? He wanted to avoid situations in which he might "accidentally" get the list right, without having truly memorized it. He figured his memory of a list was not very stable if he could not reproduce the list correctly twice in a row. So two perfect recalls seemed like a reasonable criterion of memorization. It is still used sometimes in studies of list learning. However, you could define any other criterion that made sense in a particular experiment.

When is a criterion of learning or memorization needed?

You do not need a criterion of learning in every experiment. If you want to find out how much a person gets out of one exposure to a list of words, you could just present a list once and test a person the next day. But if you are interested in studying how long a memory lasts, you must be sure the memory is fully formed. A criterion of memorization or criterion of learning defines the point at which material is considered to be really learned or memorized.

What is a retention interval?

After reaching his criterion of learning, Ebbinghaus waited for a length of time called the retention interval during which the information had to be held (retained) in memory. The retention interval is defined as the time from the last presentation of the material (the last trial) to the test. Ebbinghaus experimented with retention intervals ranging from several minutes to several days.

What measurement technique did Ebbinghaus use?

Finally, after the retention interval, memory has to be tested or measured in some way. Ebbinghaus tested his memory by relearning the same list. Naturally, he required fewer trials to learn the list a second time. Ebbinghaus measured the strength of memory by the savings that occurred between the first and second learning periods. If it took 10 trials to learn a list to the criterion of two perfect recalls the first time and 5 trials the second time, he called this 50% savings.

In what sense is relearning a powerful measure of memory?

The savings measure is not used very much in today's memory research. However, it represents a powerful way of measuring memory called relearning. Relearning can show the effects of experience long after other types of memory vanish. For example, a student who is exposed to a foreign language as a child may find that he or she learns the language quickly in a college course, compared to other students. Even if little conscious memory remains, memory for the language is revealed by "savings" or unusually rapid learning the second time.

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