Much of what we know today about how the brain works has come from studies of brain disorders and diseases. Knowing this, it shouldn’t be too surprising then that our knowledge about the spacing effect may have come from French psychologist Théodule-Armand Ribot’s work on amneisa.

Ribot proposed Ribot’s Law of Retrograde Amnesia in his 1881 publication titled The Diseases of Memory. The word amnesia comes from the Greek word for forgetfulness, amnēsía (source).

Simply put, amnesia refers to partial or complete memory loss, and retrograde amnesia refers to partial or complete memory loss of information acquired prior to the onset of amnesia (source).

Ribot observed from clinical trials that memories formed closer in time to a brain injury (amnesia) are impaired to a higher degree than memories formed longer in time before the injury. The key insight from Ribot’s Law is that the more time memories have to consolidate, the less vulnerable they become to impairment as a result of trauma to the brain (source).

He derived a mathematical equation from his results, which he published in his 1885 work titled Memory: A Contribution to Experimental Psychology. Ebbinghaus’s equation was later plotted as a graph known as the forgetting curve.

To quote Ebbinghaus:

Jost’s Law basically states that when two memories are equal in strength, but different in ages, the memory formed first will be strengthened the most from extra learning trials. Also, the memory formed first will decay more slowly than the younger memory over a given time interval (source).

The vital works of Ribot, Ebbinghaus, and Jost, paved the way for a large body of research on the subject, which followed in both the 20th and 21st centuries. Most modern research still confirms the ideas of Ebbinghaus, Ribot, and Jost.

This figure shows the components of a typical experiment, as was described above. Inspired by Figure 1 by Sharen K. Carpenter.

Spacing gap: The time interval that passes between study sessions.

Test delay: The time interval between the last study session and the final test.

Spaced vs Massed Practice

Research Studies

The neuron (also known as the nerve cell) is the main functional unit of the nervous system. In popular culture, neurons are sometimes called simply “brain cells.” Neurons process and transmit information between other nerve cells, muscles, and glands, using electro-chemical signaling.

 

 

New neurons are formed from precursors in the dentate gyrus of the hippocampal formation, which is a central brain region involved in learning and memory. This process is known as neurogenesis, and generates thousands of new neurons continuously each day. The average human brain is made up of approximately 100 billion neurons.

 

 

 

Out of the thousands of neurons created daily, the majority of them die shortly after their birth. The researchers in the study hypothesized that rats trained with spaced trials would have more neurons rescued from death than rats trained with massed trials. 

The study consisted of two experiments. In the first experiment, Sprague-Dawley rats (a common rat strain used in research) were injected with bromodeoxyuridine to detect the formation of new neurons. 

The researchers hypothesized that more new neurons would be saved from death in a group of rats trained with spacing trials, than in a group of rats trained with massed trials. training 

The researchers then divided the rats into two groups, where one group of rats (group 1) were trained to complete a task using spaced trials, and the other group (group 2) were trained to complete the same task using massed trials. 

The time it took for the rats to go through the maze to reach a platform was measured during each trial. The video below does an outstanding job of demonstrating how the Morris Water Maze is used in experiments! I’d highly recommend watching it!

 

You guessed it, the food chain was the topic the researchers tested the children on during the experiment. None of the children had been taught anything about the food chain in school before the study was conducted, so presumably it was all new information for them unless they had parents who put on Bill Nye a lot around the house. 

The children in the massed condition were given four lessons–one after the other–in the same day, while the children in the spaced condition were given one lesson a day for 4 days. The children in the clumped condition were given two lessons in immediate succession on the same day when the children in the massed condition were taught, and then another two lessons that were also in immediate succession the next day. Each condition had exactly 12 children in it.

The children were given a pre-test before they were given the lessons, and then an identical post-test after they were given all of the lessons, in which the questions were designed to gauge generalization. Interestingly, the children’s change in performance in the clumped and massed conditions were roughly equivalent, and the children’s change in performance in the spaced group was much better.

This study not only gives us more evidence that spaced learning is superior over massed learning for memory retention, but also suggests that learning by spaced methods may boost one’s ability to generalize the information to new situations. 

If you can recall learned material again effortlessly during your second study session, then the interval wasn’t long enough. It should be challenging to try to recall the material, but not to the point of frustration.

In addition to the intuitive approach, you can also use a program with a computer algorithm like SuperMemo, Anki, or Quizlet to approximate the optimal intervals.

SuperMemo is a computer program that uses an algorithm to approximate the optimum time intervals between study sessions for long-term retention. At the program’s launch back in 1987, SuperMemo used what’s known as the SM-2 algorithm to approximate the intervals. 

Given that this was a long time ago, we should add that SuperMemo has since upgraded to the SM-17 algorithm. Anki is a newer spaced repetition flashcard system that’s based on the same algorithm, but with slightly different features.

While some students use these systems successfully, many say the major drawback is that they’re both pretty complicated to learn how to use. I’ve never personally used SuperMemo, but I used to use Anki regularly to study. I can testify that Anki does have a somewhat steep learning curve, but it is pretty awesome once you get the hang of how to use it!

For the sake of simplicity, I highly recommend using Quizlet’s long-term learning mode, which is based on spaced repetition. The only downside is that you have to pay to upgrade to Quizlet Pro to use this feature.

Although Quizlet is not nearly as powerful as Anki or SuperMemo, with a little creativity, you can utilize many of the best features of Anki and SuperMemo within your Quizlet decks! I’m going to show you how to do this right now!

Flashcard spaced repetition Study Tips

In order to memorize this, she makes the following flashcard on Quizlet:

 

Keep in mind that this is just one card that covers only a tiny fraction of the total notes that Becky needs to memorize! The first time Becky cycles through her deck and gets to this card, she is able to recall recall the first two components of the blood, and she recalls the two facts associated with red blood cells, but can’t recall any of the other components, or their associated facts. After reviewing this card, Becky puts it in the bottom of the deck and works on some other cards. 

When she gets back to the card for the second time, she is able to recall the same info as she was the first time, and also remembers another fact associated with white blood cells, but she’s unable to recall the rest of the information!

It’s certainly possible for Becky to memorize everything this way, but there’s a much better way to go about it! Becky would be much better off if she broke the information down into smaller, simpler chunks. To illustrate this, let’s focus on just her notes for the first component of blood:

Blood contains red blood cells (aka erythrocytes, transport oxygen).

The simplest way to make a great flashcard out of this is to use the underscore key to “blank out” parts of the notes. To do this, simply hold down the shift button and press the key highlighted in red immediately to the left of the plus/equals sign key, shown on the keyboard below. Depending on the type of computer you’re using, you may or may not need to press enter after.

The basic principle here is very similar to what SuperMemo and Anki users call making a “cloze deletion.” Here’s an example of some of the Quizlet cards she could create using this method:

 

Another very simple way Becky could make excellent flashcards is to take each bit of information and turn it into a separate question. For example:

 

The advantage of this method over the first is that there is less information on the cards, making it even faster for Becky to review them. The third method involves making true/false statements, just like this:

Please note how Becky included a brief explanation in the first true/false section. Another awesome perk to using Quizlet is that you can put a virtually unlimited amount of information on the card! 

To be clear, when Becky studies this card, she only has to answer true or false. She doesn’t need to recite the explanation; she merely included it for reference.

The fourth and final method that we’re going to cover here may require a little more creativity for some, but it can be devastatingly effective when it’s done well! 

This method is what I call the multiple choice method. It basically involves picking part of the information that you’d like to learn, and then making up “bogus” answer choices. Here’s an example of one way Becky could do this:

Again, when Becky reviews this card, she only has to pick answer choice B, she doesn’t have to recite the explanation; it’s only there incase she wants to reference it (but it wouldn’t hurt to read it quickly each time she checks the answer!).

We’ve just seen how Becky can design flashcards for the first part of her notes using the 4 different methods we’ve outlined here. As a summary, here are the four methods:

1. Single missing keyword cards
2. Single question cards
3. True/false cards
4. Multiple choice cards

In practice, Becky would finish making cards out of the rest of this section of the notes, and would then repeat the process for the rest of her notes from this lecture. Her goal would be to cover everything important using at least 2 – 3 different methods. She would then shuffle the deck completely, so that the questions would be fed to her in random order.

The whole point here is that after optimizing her deck for maximum efficiency, Becky would then study using the Quizlet long-term learning feature or Anki/SuperMemo, either of which would automatically determine the best intervals for her based on her performance. For example, she would be would shown the cards she needs the most work on more frequently than the cards she knows the best.