Testing between intervals: a key to retaining information in long-term memory
The proverb “practice makes perfect” highlights the importance of repetition to master a skill. This principle also applies to learning vocabulary and other material. In order to fight our natural tendency to forget information, it is essential to reactivate it in our memory. But, how often?
Research in cognitive psychology provides answers to this question. However, it is also important to understand underlying principles of long-term learning to apply them in a useful and personalised way.
The ‘spacing effect’
There are two key principles for memorising information in the long term.
First, test yourself to learn and review content. It is much more effective to do this using question-and-answer cards than just to reread the material. After each attempt to recall pieces of information, review the one that could not be retrieved.
The second principle is to space out reactivations over time. This phenomenon, known as the “spacing effect”, suggests that when reviews of specific content are limited to, for instance, three sessions, it is preferable to space them over relatively longer periods (eg every three days) rather than shorter ones (every day).
Reviewing material at long intervals requires more effort, because it is more difficult to recall information after three days than one. However, it is precisely this effort that reinforces memories and promotes long-term retention.
When it comes to learning, we must therefore be wary of effortlessness: easily remembering a lesson today does not indicate how likely we are to remember it in a month, even though this feeling of easiness can cause us to mistakenly believe that review is unnecessary.
Robert Bjork of the University of California coined the term “desirable difficulty” to describe an optimal level of difficulty between two extremes. The first extreme corresponds to learning that is too easy (and therefore ineffective in the long run), while the other extreme corresponds to learning that is too difficult (and therefore ineffective and discouraging).
Finding the right pace
There is a limit to how much time can pass between information retrievals. After a long delay, such as a year, information will have greatly declined in memory and will be difficult, if not impossible, to recall. This situation may generate negative emotions and force us to start learning from scratch, rendering our previous efforts useless.
The key is to identify the right interval between retrievals, ensuring it is not too long and not too short. The ideal interval varies depending on several factors, such as the type of information that needs to be learned or the history of that learning. Some learning software use algorithms taking these factors into account, to test each piece of information at the “ideal” time.
There are also paper-and-pencil methods. The simplest method is to follow an “expansive” schedule, which uses increasingly longer intervals between sessions. This technique is used in the “méthode des J” (method of days), which some students may be familiar with. The effectiveness of this method lies in a gradual strengthening of the memory.
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When you first learn something, retention is fragile, and memorised content needs to be reactivated quickly not to be forgotten. Each retrieval strengthens the memory, allowing the next retrieval opportunity to be delayed. Another consequence is that each retrieval is moderately difficult, which places the learner at a “desirable” level of difficulty.
Here is an example of an expansive schedule for a given piece of content: Day 1, Day 2, D5, D15, D44, D145, D415, etc. In this schedule, the interval length triples from one session to the next: 24 hours between Day 1 and Day 2, then three days between D2 and D5, and so on.
Gradually incorporating new knowledge
There is no scientific consensus on the optimal interval schedule. However, carrying out the first retrieval on the day after the initial moment of learning (thus, on D2) seems beneficial, as a night’s sleep allows the brain to restructure and/or reinforce knowledge learned the previous day. The subsequent intervals can be adjusted according to individual constraints.
This method is flexible; if necessary, a session can be postponed a few days before or after the scheduled date without affecting long-term effectiveness. It is the principle of regular retrieval that is key here.
The expansive schedule also has a considerable practical advantage in that it allows new information to be gradually integrated. For instance, new content can be introduced on D3, because no session on the initial content is scheduled for that day. Adding content gradually makes it possible to memorise large amounts of information in a lasting way without spending more time studying it.
The other method is based on the Leitner box system. In this case, the length of interval before the next retrieval depends on the outcome of the attempt to retrieve information from memory. If the answer was easily retrieved, the next retrieval should happen in a week. If the answer was retrieved with difficulty, then three days need to elapse before the next test. If the answer could not be retrieved, the next test should take place the following day. With experience, you will be able to adjust these intervals and develop your own system.
In short, effective and lasting learning not only requires that a certain amount of effort be made to retrieve information from memory, but a regular repetition of this process, at appropriate intervals, to thwart the process of forgetting.
Émilie Gerbier ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'a déclaré aucune autre affiliation que son organisme de recherche.
Auteur : Émilie Gerbier, Maîtresse de Conférence en Psychologie, Université Côte d’Azur
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