If you’ve been to a Learning and the Brain conference in the last 26 years, you’ve heard at least one speaker talk about the importance of working memory. Your working memory – typically abbreviated WM – allows your mind to hold a few bits of information and then reorganize and combine them into something new.
For example, imagine I say to you “without writing anything down, alphabetize the workdays of the week.”
You start by recalling those days in the order they occur: “Monday, Tuesday, Wednesday, Thursday, Friday.” Now that you’re holding those bits of information, you can reorganize them in your mind: “Friday, Monday, Thursday, Tuesday, Wednesday.” Voila: that was working memory.
You can quickly see that WM is at the core of all academic learning. To learn (almost) anything new, students must use their working memory.
For that reason, discussions of WM typically stress this alarming point: we just don’t have very much working memory. For instance: recall that alphabetizing task I gave you a few paragraphs ago. When I ask teachers to do that in a workshop, most of them succeed. But a few minutes later, when I ask them to alphabetize 10 months of the year, they laugh nervously and give up almost immediately.
In brief: alphabetize 5, no problem. Alphabetize 10, no can do. This realization guides almost everything we do as teachers.
The Size of The Problem
The importance of these insights leads to an obvious question. We know that working memory is small…but just how small? Exactly how narrow is this cognitive bottleneck that constricts students’ thinking?
The best-known answer comes from a well-known article by George Miller, written way back in 1956. His clever title tells us what we need to know: “The Magical Number Seven Plus or Minus Two.” Miller’s formula says, basically, that adults have, roughly, 7 “slots” in WM. Some folks have lower WM capacity – perhaps as low as 5. Others reach higher – up to 9. Voila: 7±2.
From one perspective, this formula makes sense. It puts plausible numbers on two experiences:
- We don’t have a lot of WM, and
- Some people have more than others
In fact, Miller’s formula helps explain that WM exercise described at the top of this blog post. Teachers successfully alphabetize the workdays of the week because there are five of them – comfortably at the low end of Miller’s range. But when I ask teachers to alphabetize 10 months, they routinely fail – because the task goes beyond the maximum of 9.
You might even have heard of another bit of support for this formula: “phone numbers were initially limited to seven digits to keep them within average WM capacity.” This claim turns out not to be true. After all, the US phone number system was developed in the 1940s, over a decade before Miller published his paper. But the popularity of this myth suggests that Miller’s argument just makes sense to many people.
Honey, I Shrunk the Memory
Despite all these reasons to adopt the 7±2 mantra, we have at least two good reasons to resist it.
First, more recent research, published by Nelson Cowan in 2001, suggests that working memory may have as few as four slots. If we accept Cowan’s revised formula, we understand even more viscerally why our students struggle with working-memory tasks in school – where almost everything is a working-memory task.
More radically, I want to propose a second reason to resist Miller’s account of seven slots. In fact, I want to move away from the idea of “slots” altogether – whether we’re talking seven or four. In my view, the “slots” explanation of working memory encourages teachers to think about the wrong thing; truthfully, it asks us to do something quite impossible. Let me explain.
When 5 ≠ 5
I suggested above that “alphabetizing five workdays” falls at the low end of Miller’s 7±2 formula. This way of thinking encourages teachers to focus on counting. In other words, we should be asking ourselves: how many specific chunks are students manipulating at this moment? If the answer is “less than seven,” then everything should be fine.
But let’s go back and look at that task. Notice that – to succeed at that task – you need to hold MANY more items in WM.
- You need to hold on to the instructions I gave you. If you didn’t keep track of the task demands, you couldn’t complete it.
- You also need to keep track of the order of the alphabet. To decide where “Thursday” fits in your revised list, you’re constantly checking in with that rhyme you learned even before kindergarten.
- By the way: how many “slots” does the order of the alphabet fill? One? Twenty-six? some other number?
This wider view of working-memory demands leads me to two conclusions:
A: Accomplishing this mental alphabetization task requires holding and processing MANY more than 5 bits of information.
B: More broadly, trying to “count slots” is an entirely futile endeavor. I’ve been using this alphabetizing test for years, and I have no useful notion of how to quantify its WM lift. I can say this: “most teachers succeed at the first; almost no one succeeds at the second.” But trying to assign a numeric value to these tasks leads to frustration and confusion – not to better teaching.
Teaching Implications
In my view, focusing on “slots” distracts us from a more useful and important task: recognizing and solving students’ working memory overload. That is, we should be good at
- Anticipating the classroom experiences that might result in overload,
- Recognizing overload when it happens, and
- Solving – or at least mitigating – those problems.
Yes, having a number like 4 or 7 in mind might be helpful background knowledge. But the real work comes not in counting, but in rethinking the work we do in the classroom. (Here’s a series of blog posts on how to do so.) Teachers will experience our teaching work differently when we start seeing learning from our students’ working-memory perspective.
Miller, G. A. (1956). The magical number seven, plus or minus two: Some limits on our capacity for processing information. Psychological review, 63(2), 81.
Cowan, N. (2001). The magical number 4 in short-term memory: A reconsideration of mental storage capacity. Behavioral and brain sciences, 24(1), 87-114.
