What the School System Never Told You about Remembering and Forgetting (Study Myths Part 3)


The traditional view of learning (which is often unconsciously assumed rather than explicitly stated) goes something like this:

If you have really and truly learned a thing, then you won’t forget it; and if you do forget it, that just proves that you never truly learned it to begin with.

Under the influence of this myth, we tend to think that the key to successful studying is to work extremely hard, making sure we really know a thing before we move onto the next. Then, once we have truly mastered the new thing, we move onto something else. Inevitably, however, reality kicks in and we forget the earlier thing we learned, leading to guilt and frustration.

This implicit myth about learning is embedded in our school system and influences us from our earliest days. The only problem is that this paradigm has been proved completely false by the discovery of what is known as the “spacing effect.”

The “spacing effect” refers to the principle that human beings and animals learn best when their learning sessions are spaced over a long period of time rather than crammed into a briefer interval. Although it may seem counter-intuitive, studying less, if spaced appropriately, is more effective than studying more.

Why Forgetting Isn’t Always a Bad Thing

Spaced learning, interspersed with periods of decreased retention, is like watering a plant. Imagine there is a plant you’re taking care of for a month, but you only have one gallon of water. Would it be more effective to use up the entire gallon of water at the beginning to give the plant a big drenching, or what it be better to water the plant little and often throughout the entire month? Obviously the second would be preferable.

The human brain is like that plant. Just as spaced watering, interspersed with periods of dryness, is the most effective watering strategy, so spaced learning is the most effective strategy for cementing long-term memories in the brain. So if you had an hour to learn something, and you spread that hour over a month, your level of retention would be better than if you used that hour up in a single day. On the other hand, if you divided those same units of study over an entire year, your rate of retention would be superior than using it up in a month.

When researching spaced learning for the Journal ‘Memory and Cognition‘, Denise Dellarosa and Lyle E Bourne Jr. from the University of Colorado shared studies proving that small repeated learning sessions are better than large single presentations. They showed that while spaced repetitions are better than non-spaced repetitions, widely-spaced repetitions are better than narrowly-spaced repetitions.  The results of the experiments proving this are represented on the graph below:


This goes completely contrary to how we are normally trained to think about learning and memory.

What You Think Everything You’ve Been Taught about Learning and Forgetting is Wrong

Over the last year I’ve been writing posts to debunk a number of myths about learning and memory that pervade our culture. (For earlier posts in this series, click here and here.) Understanding about the spacing effect allows us to debunk yet another myth. The myth is that learning occurs in one-time events, and that relearning is at most a necessary evil. Think about the way our school system gives a disproportionate amount of attention to the initial act of learning, while encouraging comparatively little focus on re-learning. At Elementary School through to college we might be expected to retain something for a whole semester, or a year at most, but the methods for measuring this, such as final exams, make it easy to simply learn the material the night before the test. The problem with this model is that it is a complete waste of time to study something if you forget it and don’t ever come back to it.

Grand Master of Memory, Ed Cooke (the memory teacher of Joshua Foer, author of Moonwalking With Einstein), has remarked on the irony that our educational system seems to be structured in such a way as to reward those who learn something once and then go away and forget it forever. Cooke observed that “An alien species trying to understand our schools would be forgiven for thinking that they have been artfully designed to train students in the art of forgetting.” Cooke continued:

Throughout school we spend our time learning information for tests. We then forget that information as soon as the test has passed. This pattern continues all year, a heroic shuffling in and out of knowledge, and we then find ourselves tasked days before crucial exams with relearning everything that we’ve managed to forget over the course of the year.

This often takes almost as much time as if we were doing it from scratch. And even when we succeed in re-learning all that, which we tend not to, we then forget it all as soon as the exam is over.

Using the analogy of watering a plant that I employed earlier, Cooke compares this type of learning to vigorously watering a plant all at once and then never coming back to water it again. With plants we know that spaced watering is effective: similarly, in the acquisition of knowledge we should not be focused on simply learning once, but on spaced-learning over time.

The Virtue of (almost) Forgetting

Have you ever had the experience where you read something and then right afterward you can only recall about 10% of it, or less? We’ve all had that experience, which is normal. It is normal because the human brain was not designed to remember something on only a single exposure.

Not only is forgetting not a bad thing, but it can be a good thing if it propels one to engage in the type of spaced learning that is a necessary precondition for genuine learning.    In one sense knowledge is based on what you learn, but in a more important sense it is based on what you re-learn following either periods of forgetfulness or decreased retention.

Ideally, spaced learning sessions should occur prior to a thing being completely forgotten. Research shows that the spacing effect works best when the interval between study sessions is equal to the time of retention, so that you re-learn material just as you’re about to forget it. However, even if you wait until after you have forgotten something, spaced learning is still preferable to non-spaced methods of learning. Moreover, there may be some benefits to completely forgetting material before the next learning session, as Dr. Will Thalheimer explains in his online book Spacing Learning Events Over Time: What the Research Says:

Spaced repetitions typically cause a temporary increase in forgetting between the times when the beneficial repetitions are delivered. Learners are prompted to forget early to remember later….spaced retrieval practice can generate learning by first prompting retrieval failure. When learners fail to retrieve information from memory, that failure can serve as a warning. Subsequent opportunities to learn information related to the previous failure generate more vigorous and constructive learning behaviors….

Does this mean that failure is always something to encourage? Absolutely not! It’s often more efficient to have learners learn the information and then help them maintain that level of memory accessibility. But since forgetting is a natural process, when learners do forget, we want that forgetting to promote the kind of cognitive processing that will engender long-term retrievability. Spaced retrieval practice does that. And what’s really convenient is that spaced retrieval practice is also the best way to maintain memory accessibility over time. So, to be absolutely clear about this, spaced retrieval practice is one of the best things we can do to maintain memory accessibility and spur productive learning behavior when memory accessibility fails.


A Paradigm Learning Shift

The spacing effect has the potential to radically transform how we approach learning. What would happen if our school systems, our colleges and even industrial learning contexts could avail themselves of the research on spaced-learning to facilitate long-term memory retrieval? If the empirical data is anything to go by, the result would be more retention with less effort.

Further Reading




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