The Ebbinghaus Forgetting Curve

The Ebbinghaus Forgetting Curve hypothesizes the decline of memory retention in time. A related concept is the strength of memory that refers to the durability that memory traces in the brain. The stronger the memory, the longer period of time that a person is able to recall it. A typical graph of the forgetting curve purports to show that humans tend to halve their memory of newly learned knowledge in a matter of days or weeks unless they consciously review the learned material. This conclusion is not currently supported by evidence since the only studies done by Ebbinghaus are on himself. This does not meet the standards for scientific research.

His first hurdle was to find a means to study “pure” learning. In his experiments, he decided to use himself as the test subject. His next problem was to find material to learn that had absolutely no meaning or relationship to anything he already knew. Ebbinghaus finally decided to use three-letter “nonsense words” which consisted of a consonant-vowel-consonant formation. For his study, he created 2,300 of these nonsense words.

His study began with him learning multiple lists of the created nonsense words. His pre-established standard was to be able to have perfect recall of the words, and he studied each list until he had them memorized. He then recorded his recall of these “words” at different time intervals ranging from 20 minutes to 31 days, all in the time span of one year.

The results of Ebbinghaus’s experiments revealed a relationship between the forgetting of learned information over time. He found that a good part of what a person forgets takes place within 20 minutes of the initial learning. Within one hour, a person forgets nearly half of what was originally learned. After 24 hours, almost 2/3 of the previously learned material is forgotten. These results are known as the “Ebbinghaus Forgetting Curve.” Three years later, Ebbinghaus repeated his experiment with similar results.

How Quickly Do We Forget?

According to Ebbinghaus, the level at which we retain information depends on a couple of things:

• The strength of your memory
• The amount of time that has passed since learning

The shape of the curve is defined by the following equation: (Warning: math ahead!) Retention = e ^ -(Time/Strength of Memory)

It’s easier to see in a graph:

Keep in mind, your unique memory strength will determine whether you retain half the information for 3 weeks (as in the graph above) or more, or less. Depending on what you’ve learned, especially classroom style, I’ve read estimates that say we forget 90% within the first month – or even first week!

So how do we help them overcome the Ebbinghaus Curve?  Well the speed of forgetting depends on a number of factors such as the meaningfulness of the information, stress level, repetition of information and the use of mnemonic techniques.

So, making the information meaningful for our learners is one way to help them remember.   It is a lot easier to remember the phone number of a favorite restaurant than 7 meaningless numbers.

As the graph below shows, Repetition of learning definitely improves retention of information.  Initially the information needs to be repeated quickly–good instructors often repeat the important information in a class.    Review of information after a class has a dramatic effect on information retention.   According to the Curve  of Forgetting: University of Waterloo, participants who spend 10 minutes reviewing information within 24 hours of receiving will raise the curve almost to 100% again. A week later, it only takes 5 minutes to “reactivate” the same material and again raise the curve. By day 30, your brain will only need 2-4 minutes to give you the feedback, “Yes, I know that…”