Combining Interleaving and the Spacing Effect, Part 1
Jonathan Firth's Memory & Metacognition Updates #125
Hello!
In a couple of recent posts I explored research that has investigated the combination of two evidence-based learning techniques: retrieval practice, and generative learning (find the posts here and here).
I mentioned in passing that even when pedagogical techniques are effective, combinations of two or more techniques don’t automatically help. I give the example of interleaving and spacing. As one reader rightly pointed out to me, this deserves further explanation!
Spacing and interleaving
First, a very brief recap:
The spacing effect relates to improved learning when practice is distributed widely over time, such that there are gaps between one practice session and the next. For example, a child learning spelling would be better to practice for 10 minutes per day over six days than to practice for one hour on a single day, even though the overall study time is the same. More information here: update #39.
Interleaving relates to the order of items and the contrast between them. When you practice multiple similar types of items (e.g. maths problems focusing on the same skill, or examples of the same concept), this is a blocked study session. When you practice items from different skills or categories such that each item has a different type of item before and after, this is an interleaved study session. More here: update #96.
Thus, spacing and interleaving are not the same thing.
It would be possible for an interleaved study session to be more or less spaced over time, while spacing practice would be possible without interleaving that practice.
Combining the two
So, why did I suggest that combining spacing and interleaving could cause problems?
This was explored by researchers Monica Birnbaum and colleagues. The study focused on the idea that interleaving helps because it contrasts items from different categories. This contrast is, according to many researchers, the reason why interleaving helps (an idea known as the discrimination-contrast hypothesis).
However, other researchers had reasoned that interleaving helps mainly because it adds a very short delay between one item and the next. If item A is presented in a block (A – A – A) then the gap between two examples is shorter (less spaced) than if it is interspersed with other categories (e.g., A – B – C – A – B – C – etc).
So, what matters – the contrast or the delay? To test this, Birnbaum and colleagues inserted additional delays between items, so that learners either saw contrasting items close together (examples from category A, B, C, etc), or with a brief delay in between the items, achieved by inserting 10-second trivia questions, like so:
Condition 1: A – B – C – etc
Condition 2: A – question – B – question – C – etc
If delays are the cause of the interleaving benefit, condition 2 should do better. But if contrast is what matters, condition 1 should be superior, and this is in fact what the researchers found.
In condition 2 (with delays), the advantage of interleaving disappeared – it was no better than blocking. It appeared that rather than helping (via spacing), short gaps had actually spoiled the contrast.
Below is the reference and a link to the paper (my description above focuses especially on experiment 2):
Birnbaum, M. S., Kornell, N., Bjork, E. L., & Bjork, R. A. (2013). Why interleaving enhances inductive learning: The roles of discrimination and retrieval. Memory & Cognition, 41(3), 392–402.
This is one of these cases where I am surprised to realise that I haven’t shared a paper sooner – it’s such an important one. I will say more about the educational implications next time!
Enjoy and have a great week.
Jonathan
Last time: Does Retrieval Practice Cause Forgetting?
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