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The spacing effect, if not the most studied learning factor, is certainly in the top five. As Harry Bahrick and Lynda Hall said in 2005, “The spacing effect is one of the oldest and best documented phenomena in the history of learning and memory research.”

The spacing effect is the finding that repetitions that are spaced over time produce better long-term remembering than the exact same repetitions spaced over a shorter amount of time or massed all together.

About 10 new scientific studies are carried out each year on the spacing effect (I counted 31 in the last three years). Why such frenzied dedication to exploring the spacing effect? Scientists want to know what causes it! It’s really rather fascinating!

To prepare for my upcoming conference presentation at the UK Learning Technologies conference (my presentation is now available on YouTube by clicking here), where they’ve asked me to speak on the spacing effect as it relates to mobile learning and microlearning, I’m doing another review of the scientific research. Here, on my blog, I’ll share tidbits of my translational research effort, especially when I find articles that are particularly interesting or informative.

In this post, I’m looking at Geoffrey Maddox’s review of the spacing research, which was published just last year in 2016 and is the most recent review available (although given the interest in spacing, there are many reviews in the scientific literature). He does a spectacular job making sense of the many strands of research.

In it, he finds that there are six main theories for why the spacing effect occurs. I’ve simplified his list into five theoretical explanations and I’ve ignored his somewhat jargony labels to help normal folks like me and you grok the meaning.

Five Theoretical Explanations for the Spacing Effect

  1. Spacing Prompts More Attention
    Learners may exert more attention to spaced items (compared with massed items).
  2. Spacing Prompts Retrieval
    Learners may be forced to retrieve spaced items (compared with massed items that need no retrieval—because they are still top of mind).
  3. Spacing Prompts More-Difficult Retrieval
    Learners may be prompted to engage in more difficult retrieval of spaced items (compared with massed items) and longer-spaced items (compared with shorter-spaced items).
  4. Spacing Involves More Contextual Variability
    Learners may create more retrieval routes (or more varied retrieval routes) when prompted with spaced items (compared with massed items).
  5. Spacing Prompts Retrieval and Variability
    Spacing benefits learners through both retrieval and variability, but variability, because it induces weaker traces may lead to more retrieval failure, thus lowering retrieval rates when spaced intervals are too long.

Maddox concludes that the only one that even comes close to explaining all the phenomenon in the scientific literature on spacing is the last one, which is really a combination of #2 and #4.

Count me as a skeptic. I just think we may be asking too much to push ourselves toward a unifying theory of spacing at this point. While a ton of research has been done, there are so many aspects to spacing and so much more authentically realistic research left to do that we ought to hold off on tying a pretty bow around one theory or another.

Evidence supporting my skepticism was found in the very next article that I read, where Metcalfe and Xu found more mind-wandering during massed practice than during spaced practice. This would fall into theory #1 above, not 5 (as Maddox recommended) or #2 or #4, which comprise 5.

Practical Implications

This article was not focused on providing practical implications, so it’s probably too much to ask of it. Nevertheless, it does show the complexity of spacing at a cognitive level.

Also, Maddox was pretty clear in describing how robust the scientific research is in terms of the spacing effect. He wrote, Because of its robustness, the spacing effect has the potential to be applied across a variety of contexts as a way of improving learning and memory.”

He also detailed the ways that the science of spacing is so strong, including the following:

  • The spacing effect is: “observed in different animal species,”
  • “across the human lifespan”
  • “with numerous experimental manipulations”
  • “observed with educationally relevant verbal materials”
  • “observed in the classroom”
  • and observed with memory impaired populations”

We as learning professionals can conclude that the spacing effect (1) is real, (2) that it applies to all human beings, (3) that it is relevant to most situations, (4) that it is a powerful learning factor, and (5) that we ought to be utilizing it in our learning designs!

So folks, as I wrote in 2006, we ought to be figure out ways to Space Learning Over Time, using spaced repetitions, perhaps in a subscription-learning format.

Research Cited:

Bahrick, H. P., & Hall, L. K. (2005). The importance of retrieval failures to long-term retention: A metacognitive explanation of the spacing effect. Journal of Memory and Language, 52, 566-577.

Maddox, G. B. (2016). Understanding the underlying mechanism of the spacing effect in verbal learning: A case for encoding variability and study-phase retrieval. Journal of Cognitive Psychology, 28(6), 684-706.

Metcalfe, J., & Xu, J. (2016). People mind wander more during massed than spaced inductive learning. Journal of Experimental Psychology: Learning, Memory, and Cognition, 42(6), 978-984.

Thalheimer, W. (2006, February). Spacing Learning Events Over Time: What the Research Says. Available at: http://work-learning.com/catalog.html.

As you know, if you’ve dabbled into my work for a few years, I’ve closely followed the research finding, “The Spacing Effect,” both from a research perspective and a practical perspective. Indeed, I was one of the first in the workplace learning field to recognize its practical significance, which I wrote about as early as 2002. In 2006 I published the research-to-practice report entitled Spacing Learning Over Time, which should — if there was justice in the world (LOL) or viable trade organizations (OUCH) — be enshrined in the Learning and Development Hall of Fame. Snickers are welcome. Taza Chocolate even better. A few years ago, still wanting to advocate for the practical use of the spacing effect, I began speaking about Subscription Learning at conferences and I developed a website (SubscriptionLearning.com) to encourage folks in the learning field to utilize the spacing effect in their learning designs. SubscriptionLearning.com is being retired in 2017, as it is no longer needed. Blog posts from the website are incorporated in this blog.

I am grateful to the enlightened organizations who have supported my work over the years and specifically to the individuals who continue to encourage the reading of the 2006 research report. Feel free to share yourself.

Now in 2017, I am grateful to another organization, Learning Technologies (in the UK) who is sponsoring me to speak on the spacing effect at their conference starting in a few weeks. As part of my efforts, I am developing a new presentation and I am updating my research compilation on the spacing effect. Stay tuned to this blog as I’m likely to share a few of my findings as I dig into the research.

Indeed, the research on spacing is some of the most interesting I’ve studied over the years. The first thing that fascinates is that there is so much damn research on the spacing effect, also referred to as spaced learning, distributed practice, and interleaving. In 1992, Bruce and Bahrick counted up the number of scientific studies on spacing and found over 300 articles at that time. Every year, there are more and more scientific articles published on spacing. By my rough count of journal articles cited on PsycINFO (a primary social-science database), over the last three years there have been 31 new articles published on the spacing effect (7 in 2014, 14 in 2015, and 10 in 2016).

One of the main reasons that so many research articles are published on the spacing effect is that the phenomenon is so intriguing. Why would spacing repetitions over time produce so much more remembering than giving the learners the exact same repetitions but simply massing them all at once or spacing them with less time in between? Freakin’ fascinating! So researchers keep digging into the complexities.

Harry Bahrick and Lynda Hall announced in 2005 that, “The spacing effect is one of the oldest and best documented phenomena in the history of learning and memory research.” And, just last year in a scientific review article, Geoffrey Maddox wrote, Because of its robustness, the spacing effect has the potential to be applied across a variety of contexts as a way of improving learning and memory.”

Stay tuned, as I hope to be be spacing my research compilations over time…

Research

Bahrick, H. P., & Hall, L. K. (2005). The importance of retrieval failures to long-term retention: A metacognitive explanation of the spacing effect. Journal of Memory and Language, 52, 566-577.

Maddox, G. B. (2016). Understanding the underlying mechanism of the spacing effect in verbal learning: A case for encoding variability and study-phase retrieval. Journal of Cognitive Psychology, 28(6), 684-706.

Thalheimer, W. (2006, February). Spacing Learning Events Over Time: What the Research Says. Available at: http://work-learning.com/catalog.html.