This post is part of a series about how to apply principles of cognitive science to teaching and learning. It’s grounded in a story about a student (here called Kyra) who inspired me to change my teaching. Read more about Kyra in My Three Biggest Teaching Mistakes. The other posts in this series can be found at Learning Hack #2: Learning is an active process–not a passive one and Learning Hack #3: Humans are terrible judges of their learning. (This means you). And if you’d like, you can also skip right to my suggestions for how to implement this principle.
Before I learned about cognitive science, I thought of memory like a filing cabinet.
I imagined that when somebody heard or saw something, they stored it in a file, and brought it out when they needed it. I thought a teacher’s job was to help students file information into their memories. So I tried to help students like Kyra make new information easy to file—to explain things clearly, to break big ideas into pieces, and to present those pieces in a logical sequence.
I’m not the only one, of course. Lots of us think of memory that way. But the more I learned about cognitive science, the less I felt that this filing cabinet model of learning worked. To show you what I mean, let’s think of how someone–let’s call her Jane–uses a real filing cabinet.
The Filing Cabinet
Jane’s just starting out in adult life. She just got her first apartment … and her first electric bill, her first phone bill, the stub from her first car payment, her first bank account, and her first paycheck from a new job. It’s a lot to keep track of, but Jane’s not worried; she’s organized. She’s also a bit old school. No e-statements for her–she’s keeping track of her new adult life with a filing cabinet.
When Jane gets her first electric bill, she pays it right away. Then she takes the bill stub to her filing cabinet. If there were already a file called “ELECTRIC BILLS” she’d put the bill stub in there, but since this is Jane’s first bill, there isn’t an ELECTRIC BILLS file. So she makes a new folder for them. Jane can file anything she wants—even if this is the first paper of any kind that Jane’s ever put in her filing cabinet.
Finding folders in a crowded cabinet is easy too. Jane just has to figure out where, alphabetically, her file is. It doesn’t matter what her file ends up next to. It could be something completely unrelated like “DISHWASHER MANUAL” or “EMERGENCY PHONE NUMBERS.” Because everything’s alphabetical, she has an easy way to find it no matter what is nearby.
Even though unlike files might be next to each other, different kinds of papers never end up in the same file. That’s the point. Jill doesn’t want her electric bills mixed in with her taxes or her phone bills or her recipes. That’s how a filing cabinet works, if your papers are mixed together, you can’t find them.
When I worked with Kyra, I thought my job was to give her files of clearly-explained, step-by-step science knowledge, so that she could store them in her memory filing cabinet. Later, when she couldn’t bring them back up again, I figured that something had gotten misfiled or lost, so I just explained things again; I just gave her the same file as last time.
The problem wasn’t that Kyra did a poor job of organizing her memory files; the problem was that Kyra’s memory wasn’t a filing cabinet at all.
The Net
Let’s go back to Jane, but this time instead of a modern young adult just starting out with her own apartment, Jane is a young fisherwoman from ancient times when everyone wove their own fishing nets. Jane is responsible; she takes fastidious care of her fishing net which is made up of lots of individual threads that overlap and cross each other. And everywhere two threads cross, Jane has knotted them together.
When Jane wants to make her net bigger so that she can catch bigger fish, she can’t just drop a new thread on it. She has to weave it in and tie it to threads that are already there. In fact, just adding one single thread on its own would be kind of pointless. The whole idea is to add lots of them—all of them knotted together.
When Jane goes fishing and wants to pull part of her net out of the water and into her boat, she doesn’t look for individual threads. She just grabs a handful of net and pulls. Eventually the part she wants comes up because it’s knotted to the part she pulled on.
Unlike the papers in a filing cabinet, the threads aren’t in separate little folders; they’re tangled together. On purpose. That’s how nets work. Since they’re all tied together, it matters which thread is knotted to which, and it also matters how often one of them is knotted. Adding a new thread by tying just one knot won’t do. It has to be tied in lots of places. The more the better.
Tying Knots: Memory is a Net
Our memories aren’t built of files, they’re built of knots—just like Jane’s net. You can physically see how apt this metaphor is if you’ve ever looked at a tangle of brain cells under a microscope. Learning is a lot like tying new threads into your net to make it bigger. If you want to add knowledge (a new thread) to your memory net, you have to 1.) tie it to pre-existing memories, 2.) pick the right memories to tie onto, and 3.) tie it over and over in lots of places. Check out this table that compares the two metaphors.
Memory is Like Knot-tying
| Filing Cabinet | Net | Memories |
| You can file any information you want regardless of what’s already there. | You can only add new threads if you tie them to threads aleardy in the net. | New knowledge is only memorable if it connects to knowledge or experiences you already have. |
| Retrieving a file doesn’t depend on what other files are nearby. Everything is just alphabetical. | You can bring any part of the net to the surface when you pull on threads connected to it. | Being able to remember something depends on the other memories it’s connected to. |
| Information is stored in a file with similar information. | The more places a thread is knotted into the net, the more secure it is and the easier it is to pull on. | The more memories some knowledge is connected to, the more durable the memory is and the easier it is to recall. |
(The evidence that convinced me that this is so, I’ll save for another blog post. Here, I’m focusing on the principle: Memory isn’t a file cabinet. It’s a net.)
The Power of the Net Analogy
This memory net analogy explains a lot of things that the file cabinet analogy doesn’t. For example, it explains why I don’t learn much by reading a Wikipedia article on gluons when it says:
“A gluon (/ˈɡluːɒn/) is an elementary particle that acts as the exchange particle (or gauge boson) for the strong force between quarks. It is analogous to the exchange of photons in the electromagnetic force between two charged particles.[6]
I have trouble finding pre-existing threads to tie this to. But later, when the same articles says, “they “glue” quarks together, forming … protons and neutrons.” Now I’ve got something I can tie a knot to! I know lots about glue. I’ve been using it since nursery school. Bonus points because I’ve also got memory threads for protons and neutrons. The reason explanations feel abstract or concrete has to do mostly with how many existing memory threads I can tie onto.
The net model also explains why memories do or don’t get triggered: I meet someone at a party, and she greets me warmly by name as if we’ve met before, but I don’t remember her at all! Fortunately, she sees my confusion and reminds me that I’d observed her classroom when I visited her school two years ago. All of a sudden, I remember her lesson on bridges and her fast-paced teaching style. “Oh, yes! How are you? Are you still teaching in Boston?” This makes sense if memories are knotted together. By pulling on the right part of my net, I can draw up just the thread I need.
Things like expertise and practice also make sense in terms of the memory net. People who seem superhumanly good at something like chess or baseball or playing the cello have gotten that way by tying knot after knot after knot. Their expertise is connected to almost everything in their lives—their friendships, their childhoods, their travels. They have such a wealth of experience in their expert domain, that drawing those threads up seems miraculously easy.
But when Kyra and I worked together, neither of us knew any of this. Neither of us paid attention to the memory threads that Kyra already had. Instead, my explaining things to her again and again was like dropping a pile of thread on her net and hoping that it stuck without being tied at all.
What We Should Have Done
After I began studying cognitive science, I began to imagine how things might have gone differently with Kyra. What if instead of just throwing new threads at her, we pulled up part of the net that she already had. What if we started by talking about what she already knew about how organisms use energy? Or even better, what if we started with something really concrete like, “Why do we need to eat?” or “Why do we die when we can’t breathe?”
If we had, Kyra might have been able to start tying new memory threads (like ideas about cellular respiration) onto threads that she already had (like eating and breathing). The new ideas would have been more likely to stay, and they’d already be knotted to the questions that make cellular respiration worth learning about in the first place.
Now when I work with students like Kyra, I think less about how to organize new information, and I think more about what knowledge students already have to tie new information onto.
So How Do You Make Connections
How do you actually tie those knots?
- Test first, learn second: In the file cabinet way of thinking, there’s no reason to try to solve a problem before you learn something. Why would you if there’s nothing in the filing cabinet yet? What good would it do to wrestle with a frustrating problem first? But in the memory net way of thinking, there is no better way to bring up the most relevant parts of your existing memory net. It works even if you can’t solve the problem, because it’s not about solving the problem yet. It’s about finding the places in your mind where you can tie in.
- Compare and contrast: Identifying similarities and differences has been shown to be one of the most effective learning strategies—a fact that the file cabinet model cannot explain. But the memory net model can. Comparing and contrasting ties together different parts of someone’s memory net. Instead of studying by describing or defining key concepts, pick two concepts and explain how they are alike or different. By the way, these comparisons don’t have to be between obvious pairs of things (mitosis vs meiosis; democracy with dictatorship). Comparing just about anything can be helpful. (How is mitosis like democracy? How is it different?)
- Connect ideas to examples: Too often we study ideas without examples. Textbooks and teachers often just offer one or two examples and hope that’s enough. This is not enough! The more examples that you connect abstract ideas to, the better. Every time you think about how something might be an example of a certain idea, you’ve tied another knot in your memory net.
- Zoom Out: Just like you wouldn’t try to make a net bigger by adding in a single thread, you’re never just trying to tie one new fact or vocab word into your memory net. You are trying to tie in a whole system of things, a little sub-net in part of the bigger memory net. Who cares what the definition of Realism is? The idea only matters if it’s tied to Romanticism and to what was happening in the world at the end of the nineteenth and beginning of the twentieth century. Ask yourself how do ideas you learn about relate to a bigger picture. If I picked a random street-level view on Google Maps, you probably couldn’t make much sense of where it was. But if I zoomed that out until you could see a whole state or country, then you have a better chance.
- Net tying tools: Sometimes it’s hard to see how things might be meaningfully connected. Maybe you’re medical student and you have to memorize the cranial nerves. Maybe you have to remember all the state capitals. It can be hard to feel like these are anything but rote tasks. What can you connect these ideas to? In times like this, you may have to create artificial connections. Here’s two examples
- Mnemonics—a mnemonic is a little memory trick. (Remember how King Philip Came Over For Great Spaghetti?) These help because they create connections to things that seem to have little meaning on their own, (like the order taxonomic groupings).
- Stories are the basic unit of meaning for the human mind. If you’re having trouble learning something, make up a story about it and you’ll make memories much stickier.
The basic idea is this. If you want to learn something, don’t focus on the information you are trying to learn; focus on how that information relates to what you already know. If you do, you will learn faster, with deeper understanding, remember more, and be better able to use what you learn.
Of course, this is harder than what we typically do–reread our notes, rehearse ideas just before the test, highlight a reading, etc. Which bring me to the second learning hack: Learning must be a challenge. Making things too easy undermines learning.