WHY PEOPLE FORGET
Forgetting is defined as the loss of information over time. Under most conditions, people recall information better soon after learning it than after a long delay; as time passes, they forget some of the information. We have all failed to remember some bit of information when we need it, so we often see forgetting as a bother. However, forgetting can also be useful because we need to continually update our memories. When we move and receive a new telephone number, we need to forget the old one and learn the new one. If you park your car every day on a large lot, you need to remember where you parked it today and not yesterday or the day before. Thus, forgetting can have an adaptive function.
Rate of Forgetting
The subject of forgetting is one of the oldest topics in experimental psychology. German philosopher Hermann Ebbinghaus initiated the scientific study of human memory in experiments that he began in 1879 and published in 1885 in his book, On Memory. Ebbinghaus developed an ingenious way to measure forgetting. In order to avoid the influence of familiar material, he created dozens of lists of nonsense syllables, which consisted of pronounceable but meaningless three-letter combinations such as XAK or CUV. He would learn a list by repeating the items in it over and over, until he could recite the list once without error. He would note how many trials or how long it took him to learn the list. He then tested his memory of the list after an interval ranging from 20 minutes to 31 days. He measured how much he had forgotten by the amount of time or the number of trials it took him to relearn the list. By conducting this experiment with many lists, Ebbinghaus found that the rate of forgetting was relatively consistent. Forgetting occurred relatively rapidly at first and then seemed to level off over time (see the accompanying chart entitled “Forgetting Curve”). Other psychologists have since confirmed that the general shape of the forgetting curve holds true for many different types of material. Some researchers have argued that with very well learned material, the curve eventually flattens out, showing no additional forgetting over time.
Ebbinghaus’s forgetting curve illustrated the loss of information from long-term memory. Researchers have also studied rate of forgetting for short-term or working memory. In one experiment, subjects heard an experimenter speak a three-letter combination (such as CYG or FTQ). The subjects’ task was to repeat back the three letters after a delay of 3, 6, 9, 12, 15, or 18 seconds. To prevent subjects from mentally rehearsing the letters during the delay, they were instructed to count backward by threes from a random three-digit number, such as 361, until signaled to recall the letters. As shown in the accompanying chart entitled “Duration of Working Memory,” forgetting occurs very rapidly in this situation. Nevertheless, it follows the same general pattern as in long-term memory, with sharp forgetting at first and then a declining rate of forgetting. Psychologists have debated for many years whether short-term and long-term forgetting have similar or different explanations.