Damage to memory structures
Scientific experiments on memory began with a bearded, shy itinerant professor, Hermann Ebbinghaus. His goal was to discover how memories are formed and how they fade. In contrast to earlier thinkers specializing in memory, Ebbinghaus was not a philosopher, but what we would now call an experimental psychologist. His goal was to move beyond speculation and put memory on a more firm scientific foundation.At the time of Ebbinghaus’s experiments—the mid-nineteenth century—a lot of emphasis was placed on rote memory: learning by constant repetition. The memory aspirant who wanted to learn the multiplication tables for instance, would repeat them over and over until they could be recited on command. The same repetitive process would be expanded to learning such facts as the geographical locations of world nations and their capitals. This emphasis on rote learning continued until well into the twentieth century. Anyone who was in primary school in the 1950s and 1960s can attest to the fact that rote memorization was still enforced and heavily relied upon.Today we tend to de-emphasize rote learning, “poll parroting” as it’s often referred to. As a result, it’s not unusual to encounter grade school students who can’t name any state capital other than their own—and sometimes not even that one. But the nineteenth century emphasis on rote memory made it natural for Ebbinghaus to carry out his experiments employing rote memory.Stimulated by Lewis Carroll’s Through the Looking Glass (1872), with its inclusion of verses of rhyming nonsense words, Ebbinghaus decided to use three letter-word combinations which had no meaning or associations. They were composed of Consonant-Vowel-Consonant combinations, what Ebbinghaus referred to as CVC trigrams made up of two consonants with a vowel between them. The two consonants must always be different (TAC was ok, but TAT was not) and the trigrams could not express any meaning (TIP or COT were not admissible) but only had the form of a word. After working for months applying these two rules, Ebbinghaus created twenty-three hundred CVC combinations. From this stockpile, Ebbinghaus wrote varying numbers of the trigrams in his notebook and, to the regular beat of a metronome, he did his best to recall them.By this means of this time-consuming, ponderous, and, for anybody but Ebbinghaus, utterly boring process, he discovered two key facts about memory. First was the forgetting curve: the loss of information that occurs after the establishment of a memory. The sharpest decline occurs in the first twenty minutes with additional decrease within the first hour. It then levels off after about a day. If you can still remember a fact or an event after a few months then the odds are quite good that you will remember it indefinitely.The learning curve is a measure of how fast one can learn new information (in Ebbinghaus’s case his recall of 2300-letter combinations). This too followed a pattern. Ebbinghaus read a list of twenty nonsense words out loud to himself and put away the list for a period of time then tried to recall as many words from the list as possible. After checking for the words missed, he repeated the process until he could remember all twenty nonsense words from the list.