The importance of spaced review

The importance of spaced review

This is Maia. She’s six months old. We adopted her from Romania, via a charity called   Paws2Rescue, which saves lots of dogs from horrible conditions.


Maia is allegedly being trained by our two young adults.

Unfortunately, they have failed to grasp that what dogs, and indeed all of us, need to learn effectively is what is called ‘spaced practice’.

When we first got Maia, I took her in the garden and taught her to come for a treat when I blew a whistle. She’s pretty treat-motivated and learned quickly.

Time has passed, one of the whistles is missing in action in the park. The other is sporadically used.

Unsurprisingly, her whistle recall is now unreliable – when she hears a whistle she thinks about it a bit – and if there is anything more interesting she ignores it and bounds off.

Unfortunately, poor Maia is on a slippery slope down Herbert Ebbinghaus’s ‘forgetting curve’.

Hermann Ebbinghaus was a German psychologist who pioneered the experimental study of memory.

Ebbinghaus conducted his research with chunks of nonsense letters, like CFQ or DTV. He memorised them and then noted how much he was able to remember after the passage of set periods of time.

The Ebbinghaus Forgetting Curve

Ebbinghaus Forgetting Curve

Since we know that memory of recently learned data is lost very quickly, we can begin to devise strategies to mitigate that.

These strategies relate to ‘spaced review’ – to repeating exposure to the same information over differing time periods, so that it becomes fixed in our long-term memory.

A familiar approach to training has long been:

  • Tell them what you are going to tell them
  • Tell them
  • Tell them what you just told them

And to some extent, we can see by the learning curve that this will work, especially if there is a bit of a gap between each repetition.

The Ebbinghaus Learning Curve

Ebbinghaus Learning Curve

The orange forgetting curve shows that if we don’t refresh what we learn, we forget it – rapidly.

But the green curve shows how information can be retained, if learners refresh their exposure to the material to be learned, at spaced intervals.

As you can see, the forgetting curve becomes flatter and less steep with every additional review, provided the review is made at the correct time. Each time you refresh the information the rate of loss decreases.

Memory improvement techniques repeatedly show that refreshing memory at lengthening intervals significantly improves memory retention. If we refresh ‘chunks’ of memory by recalling them at increasingly longer intervals we make that memory really long-lasting.

Making the traffic along a neural pathway regular, and frequent, means that the brain will use its plasticity to strengthen that pathway. Recent research has shown conclusively that our brains are ‘plastic’. This means that they can change and built new connections, no matter how old we are.

Here’s a bird’s eye view of a common near my home. This is a big green open space. People use it as a place to walk dogs and as a short cut.


There are no specified paths. And yet you can see from this image exactly where the routes that people take most frequently lie.

The day after someone walked across the common in a new direction for the first time, there would not be much trace of their passing.

After a week of one person walking the same route, the grass would be a bit flattened and someone else might notice the route and follow it.

As more and more people use the route, the stronger, more clearly visible and more permanent it becomes, so that even when the common is knee high in grass it is still possible to follow the paths.

This is exactly how memory works.

To turn short-term memories into long-term ones, our brains must encode, or define, the information and decide where to store it. If we have any memories to which it can be related, a neural pathway is created between them.

Every time you activate and review the new information the memory traces become stronger.

Every time you link that memory with another memory, the memory traces become stronger.

Long-term memory retrieval requires revisiting the neural pathways the brain formed. The strength of those pathways determines how quickly you recall the memory. To reinforce that initial memory, it must move multiple times across the nerve cells, retracing its steps.

The stronger the memory, the longer and more readily you are able to recall the information.

Therefore, the learning curve becomes flatter, as you retain the information for longer – so that the interval over which you need to review and refresh it becomes longer.

I remembered this in the summer, on my annual Welsh holiday. Last year, in a webinar that I delivered just before it, I was talking about the creature that makes these amazing structures on the beach.

Sabellaria Alveolata

I’d always taken them for granted, but apparently they are quite rare in the UK. They are made by a bristle worm called Sabellaria Alveolata.

Two years ago, I had never heard of it. But then I wrote my webinar, and the words ended up in my head. Sabellaria Alveolata – the name trips pleasingly off the tongue and so I have occasionally thought of it since. Walking along the beach, its name came immediately and unsought into my head, because I have strengthened the neural pathways to the memory.

For some information the interval after which you revisit can become several years.

Many years ago, I sat on a plane, reading a book about genetics. It was talking about the fundamental units of the genetic code that make up DNA. They were designated by letters: A, C, G and T.

After half an hour of flicking back and forth between where I was in the book, and where it told me their meanings, I decided to learn them. And every so often, something triggers that memory and those names appear in my head: Adenine, Cystosine, Guanine and Thymine.

Parents who have read the same book, every night for months, to a young child will have experienced this phenomenon. My children loved ‘The Cross with us Rhinoceros’, and even now, probably 14 years since I last read it, I can recite: ‘There was Willy, there was Wally, there was Tilly, there was I; Four fine brave adventurers, beneath a bright blue sky’. I never set out to learn it. But it was well and truly embedded all the same.

You will no doubt have lots of similar, really solid memories that don’t even feel like memories, they are so automatic. They’re not things you remember, they are things that you know.

What does this tell us about how we can retain the things we are trying to learn? 

By looking at the learning curve, we can see that frequent spaced review can help retention, but over time, we still tend to forget what we’ve learned.

Some memory experts argue that you can increase retention by paying attention to the way in which the information is presented to learners.

The Fuzzy Trace Theory of memory holds that we remember things in both a ‘verbatim’ manner and a ‘gist’ manner – as in ‘I can’t translate the exact words in that French sentence, but I get the gist of it’.

The gist is the most   important   piece  of   information  about something, or   general   information  without   details.

Let’s use an example close to my heart! If we think of a bar worker being asked to learn about a new craft gin, then the gist would be ‘gin, alcohol, spirit’ whereas the verbatim memory would be ‘Pollination Gin, award winning, botanicals, made in Corris, bottle design, glass to be used, garnish to be used, types of tonic that go well with it, price’.

Since both sets of information are stored, the more we can help the learner to register both the gist and the verbatim information clearly, the better we can help to prepare them to store it.

What techniques can we use to help with retention?

Link to pre-existing knowledge

Is there any way in which we can flag up the link between the new information and any existing knowledge that the learner may already have? Can we help them to use memory hooks / mnemonic devices to represent the new information in a way that links it to already familiar concepts?

The more relevant, meaningful connections you can make with the new information in your mind with things you already know, the better your memory retention over time.

Why does it matter?

Can we help the learner to regard the information as important to them? Attaching higher importance to information makes it more likely to be remembered. If you learn something, and it is important to you, and you can connect it with many things you already know, your memory retention will be very high.

How lengthy and complex is the information?

Can the information be simplified? Chunking information into concise related information makes the retrieval easier. Ebbinghaus remembered random letters in groups of threes rather than in long strings.

Spaced practice

If a learner doesn’t believe that the thing to be learned is important to them, and it doesn’t connect to anything that they already know, then constant repetition is a good strategy. Reviewing the information frequently at first when the rate of memory loss is highest, and then at regular, but lengthening, intervals will give the best opportunity for it to transfer to long term memory.

If this sounds familiar, it is of course the rote learning (‘two times two is four’) that many of us will have done as children to internalise core concepts.

When learners revisit learning at their regular, spaced intervals, the brain needs to be actively engaged. This is why question practice is so effective, as the brain is actively engaged in seeking to retrieve the original information.

Think of the different mental processes involved in reciting your eight times table, which becomes habitual and practiced, and having to state rapidly what eight times eight is.

Asking the brain to retrieve the specific information makes the neural pathway stronger and brighter, in turn making retrieval easier and easier with each successive review.