Time to forget Ebbinghaus’ forgetting curve?

Over the last decade, the conversation around cognitive science and psychology in education has grown ever louder, to the point at which these discourses have come to be seen as one of the dominant theories in contemporary education. Much of the discussion focuses on pedagogy including the role of memory and remembering, with theories of learning and teaching being based on the retrieval of information in the long term. Although the ability to remember information accurately is undoubtedly an important aspect of learning, forgetting is an important issue to consider when thinking about learning and seems to be not as widely discussed within education.

This blog will discuss the seminal work by Ebbinghaus and explore its role in the educational conversation and the many iterations of the forgetting curve which have emerged through teachers applying this to pedagogy.

Hermann Ebbinghaus

Ebbinghaus was an experimental psychologist who was interested in finding a mathematical relationship between the elapsed time post learning and forgetting. He conducted a number of experiments in the early 1880s in order to establish this.

In his experiments, Ebbinghaus attempted to learn a row of thirteen nonsense syllables until he was able to freely recall each one in the correct order. After a preset time interval, he would relearn the syllables, given the fact he had forgotten them, until he could once again freely recall each one in the correct order.  

It is important to recognise that Ebbinghaus’ view on forgetting was not a measure of how many syllables that could be recalled after a specific amount of time but the amount of time, or repetitions, it took to relearn the same list of syllables after forgetting. A measure he called savings. Savings can be presented as a decimal or a percentage and is calculated as follows:

If it took someone initially 10 minutes to learn the syllables but it only took them 8 minutes to relearn after a set time then the saving is 2 minutes. Savings is the 2/10 = 0.2

If the relearning took the same amount of time, then the savings would be 0 and if there was perfect recall without relearning, the saving would be 1 or 100%.

The original experimental results have been successfully replicated a number of times, but I am going to use data from the study by Murre and Dros in 2015 (paper can be found here) to discuss the forgetting curve due to the fidelity of their experiment. In their paper, Murre and Dros replicated Ebbinghaus’ experimental procedure and calculated savings using time. The resulting forgetting curve on a linear time scale is shown below:

The curve shows a general exponential decrease in savings. What is interesting is the higher than expected result for 1 day. Ebbinghaus also found this but he was able to fit the data point to the curve generated from his ‘forgetting equation’ so he overlooked this at the time. However, he did replicate, along with other subsequent researchers, this result after the publication of his work. This decrease or ‘slowing’ of forgetting from these experiments is thought to be due to the role of sleep in memory consolidation.

Interestingly, Murre and Dros recorded the number of correct responses (correct syllable in the correct position) during the relearning phases of their experiments. What this showed is that the proportion of correct answers after 20 minutes was marginally above 0.3 and this only decreased slightly at the longer time intervals.

Should we forget the curve?

From a position of experimental psychology the work of Ebbinghaus needs to be studied and remembered as it paved the way for psychology to have robust methods and rigour in the design of experiments that are still used today. The fact that the results of Ebbinghaus have been replicated a number of times is testament to this.

In terms of the educational conversation, it is useful to ask if we actually need a mathematical model (the graph with numbers) to tell us that learners forget. It is clear that what the Ebbinghaus’ forgetting curve does show is that:

1. a high proportion of information that is learnt is rapidly forgotten 

2. the longer you leave before relearning something, the longer it will take you to relearn

I think I would be hard pushed to find a teacher that genuinely would disagree with these statements, with or without knowledge of the curve. The question we ask then, what use does awareness of Ebbinghaus’ curve brings to a teacher beyond the knowledge that forgetting takes place over a period of time after the point of learning?

Certainly, the misinterpretation and misrepresentation of the curve is not helpful. Making claims like “you only remember x% of information after y time” is clearly untrue if you are using Ebbinghaus as your evidence base. Applying ideas like this to education is widely problematic and can result in unhelpful numbered things about forgetting, models like the infamous learning pyramid.

Additionally, there is a danger with using a mathematical model rather than just having good awareness that forgetting takes place and that there are well researched methods to remedy this. For example, we might say we forget 50% of something we have learned within an hour. This sounds plausible and whilst you might worry about all the different permutations, that’s the least of the problems. Using that premise, I could simply say, well I’ll double the information learned at the start and then they won’t forget what I intended them to learn. And of course, the teacher in you will say that’s nonsense.

Being focused on forgetting is a good thing, but it is important to think critically in our application of science just like Ebbinghaus himself was.