Chapter 2, page 52
Forgetting
We have discussed the many ways in which the mind remembers, stores and retrieves information.
However, people do not only remember information. They also forget. Forgetting is universal. In a series
of famous experiments, Hermann Ebbinghaus (1885/1987) tested how well he could recall numerous lists
of nonsense syllables. He found that after just 31 days, he could recall fewer than 30% of the nonsense
syllabus in lists he had memorized. Forgetting was rapid in the first 24 hours and then decreased only very
slowly after that. This is a general finding: People forget some of what they learn, and they tend to forget
most rapidly soon after the learning period is over (A. D. Baddeley, 1999).
However, according to researchers, people forget less than they think they do. I have heard students
say that they have forgotten everything in courses they have taken within a month of two of their final
exams. However, researchers have found that people in fact, they remember a great deal of what they
learn in college courses (Conway, Cohen, & Stanhope, 1991; Semb & Ellis, 1994). In one study,
biochemistry students could recall more than 80% of what they had learned 24 weeks after the course
ended (P. L. Schwartz, 1981). Likewise, George Semb and his colleagues (1993) found that although
students recalled less than 50% of what they had learned in a child psychology course 44 weeks later, their
performance on recognition tests was 75%, as was their performance on assessments of cognitive skills
(such as the ability to apply concepts). In a longitudinal study, Harry Bahrick and Elizabeth Phelps (1987)
tracked students who had taken a Spanish course 50 years earlier and tracked how much they had retained
after 50 years. Forgetting was most rapid over the first year, and there was relatively little additional
forgetting from years 10 to 50. In some areas, such as Spanish grammar, there is relatively little forgetting
over many years (Bahrick, 1984). Students who did well in the class maintained their initial advantage for
50 years. And given that initial recall was 37% for students who did well right at the end of class and 22%
after 50 years, these students recalled more than half of what they knew at the end of the course 50 years
later. Not all studies show such high levels of recall (e.g., Ellis, Semb, & Cole, 1998), but overall
performance has typically been fairly good in these studies.
Several factors mediate how slowly or rapidly forgetting proceeds (Semb & Ellis, 1994):
x Initial learning. Initial learning is an important factor in retaining information over time. The more you
learn initially while you are taking the course, the more you will remember years later.
x Repeated use of ideas. Even occasional use of ideas dramatically improves very-long-term memory. If
you take just one test of how much you remember, you dramatically decrease long-term forgetting on
other tests months or years later. If you continue to use ideas in later coursework or in life, retention is
high.
x Spaced study. Information, such as Spanish vocabulary, that is learned over study periods that are
spread out over time (rather than being crammed into one or two study periods) is much better retained
(Bahrick & Phelps, 1987). For example, it is more effective to study 1 hour a day for 7 days than to
study 7 hours in a single day.
There are two main theories of why forgetting occurs: the fading theory and the interference theory
(see A. D. Baddeley, 1999). According to the fading theory, memory traces fade away over time.
According to the interference theory, forgetting occurs because people lose the ability to retrieve
memories as new memories are added to LTM, making it harder to locate information. As a result, they
lose retrieval pathways that can succeed at getting at the information. It is difficult to definitively
distinguish between these two theories because as time passes, people accumulate more interfering
memories. Most theorists would agree, however, that at least some forgetting results from interference (see
A. D. Baddeley, 1999).