Memory’s Two Components: Storage and Retrieval

A photo album with a few photos taken out of it

Imagine you’re at your high school reunion. A man walks up and shakes your hand, saying how good it is to see you. You recognize them, but can’t recall their name. Luckily, someone else in your group rescues you by chiming in, “Charlie! How have you been?”

Oh right, Charlie, you think. I knew that.

And you’re right, you did know that, at least in the sense that his name was stored in your brain. Your inability to remember his name wasn’t a problem with storage but with retrieval. In How We Learn, Benedict Carey explains the difference between these two aspects of memory:

“Any memory has two strengths, a storage strength and a retrieval strength. Storage strength is just that, a measure of how well learned something is. It builds up steadily with studying, and more sharply with use. … Retrieval strength, on the other hand, is a measure of how easily a nugget of information comes to mind. It, too, increases with studying, and with use. Without reinforcement, however, retrieval strength drops off quickly.”1

Learning isn’t just about storage.

The big idea here is that learning isn’t just about getting information into your brain; it’s also about cultivating the ability to pull that information out when you need it. Storage without retrieval is useless because, while you may have the information somewhere in your brain, you can’t put it to use or prove that you know it on a test. And, of course, retrieval without storage is useless too – like having the key to an empty storage unit.

Usually, the problem we have isn’t a lack of storage, but that we have storage without retrieval. The information is in our brain … somewhere. The problem is we can’t access it.

This reminds me of the difference between familiarity and true knowledge. Truly knowing something means having both strong storage and strong retrieval for a piece of information. True knowing is seeing that man at your high school reunion and saying, “Hi Charlie!” without hesitation.

(Note: Read this if you want to get better at remembering names.)

Forgetting, Updated

This distinction gives us a new way to think about forgetting. When we forgot Charlie’s name, it wasn’t so much that his name wasn’t stored in our brains but that we’d lost the ability to retrieve it.

Thus, we should update the “use it or lose it” principle of memory: If you’ve done the work to create a strongly stored memory, you won’t necessarily lose that memory if you stop using it, but you will lose the ability to recall the information with ease. Much of the time, forgetting is just that – not losing the information, but losing the ability to retrieve it.

And this begs the question, why would we store information that we’re unable to retrieve? The answer has to do with human nature, as Carey explains:

“In its nomadic hominid youth, the brain was continually refreshing its mental map to adapt to changing weather, terrain, and predators. Retrieval strength evolved to update information quickly, keeping the most relevant details handy. It lives for the day. Storage strength, on the other hand, evolved so that old tricks could be relearned, and fast, if needed. Seasons pass, but they repeat; so do weather and terrain. Storage strength plans for the future.”1

For a student, “the future” might be a final exam. Let’s use AP US History as an example. Throughout the school year, you learn the history of the United States in chronological order. You work hard to store the information from the first unit in your brain, and you quiz yourself prior to the unit test so that your retrieval strength is strong. But then the class moves on to the next unit, and you stop working on retrieval for the previous unit. It’s still stored though, so when it comes time to review for the AP test, you don’t have to completely relearn all the material; you just have to build back up your retrieval strength. This kind of forgetting is okay, as long as you refresh your ability to recall the information before the final.

“The old dog quickly relearns old tricks.” –Benedict Carey1

Developing Both Storage and Retrieval

Memories are formed via a process called encoding, through which information is taken in and understood. If the encoding is successful, the information will be stored in short-term memory for short-term use. If enough work is done with that information, it will become stored in long-term memory.2

So your first goal in studying something is to get it stored in long-term memory. This almost always involves writing because the effort of putting pen to paper does a great job convincing your brain to care enough about the information to hold onto it. It also helps to verbalize as you study.

Many students falter at this step, only doing enough work to store the information in short-term memory. They “get it” enough to do the homework and pass the quiz, but then they stop there and slip back down the mastery path’s muddy slope. To make it stick in long-term memory, you have to keep working with it beyond the initial encoding.

If you do do the work of building up storage strength for the memory, great, but you’re still not done. You also need to develop retrieval strength, so you can actually access the information when you need it.

So your next goal in studying is to force yourself to recall the information. This means taking practice tests, doing brain dumps, doing mental recall practice, and teaching it to other people. All of these techniques build up the retrieval strength of the memory.

The need for both storage and retrieval helps explain why both massed practice and interleaving are so important. Massed practice builds up the storage strength for whatever it is you’re learning by having you drill a particular type of problem over and over again. But once that’s done, you should switch to interleaving – in which the problem types are mixed up randomly – so you’re forced to practice retrieving the proper techniques for solving each different type of problem.

Spaced repetition has a role to play here too. Revisiting a topic repeatedly over time reinforces both storage and retrieval. And critically, you don’t want to do this immediately after learning something. You need to wait a little while – an hour or two if something is brand new and longer as your memory strengthens – in order to make the recall difficult.

“The harder we have to work to retrieve a memory, the greater the subsequent spike in retrieval and storage strength (learning).” – Benedict Carey1

There’s a sweet spot to aim for, where we’re on the verge of forgetting, but we can still retrieve the information. When you work with the information again at that moment, you’re not only rescuing the memory from being forgotten but also strengthening the memory for future use.

Multiple Choice vs. Short Answer/Essay

Neither storage nor retrieval is all-or-nothing. Most students walk into their exams with a medium-to-high level of storage for the information on the test, but with a low-to-medium level of retrieval for it. Such students will tend to do much better on multiple-choice questions than they will on short-answer or essay questions.

Multiple choice questions provide an aide in retrieval, allowing you to simply recognize the correct answer from a short list of options. Questions that require you to write your own answer are much harder because they don’t give you any cues or clues to make retrieval easier. Developing your retrieval strength for the information is always important, but it’s especially important if you’re going to have to self-generate the answers on your test.

This also applies to situations – both in and out of school – that demand creative problem-solving. Since innovation is all about combinations of ideas, you’ll be far more creative if you have a large bank of ideas to draw upon that you can actually make withdrawals from. Real-world problems don’t present you with a ready-made list of potential answers. Instead, they demand that you draw upon your knowledge to come up with a solution.

And as the high school reunion example demonstrates, life isn’t multiple choice. What we usually need is true knowledge – which means both strong storage and strong retrieval.

1 Carey, Benedict. How We Learn: The Surprising Truth About When, Where, and Why it Happens. Random House, 2014.

2 “How Memory Works.” The Derek Bok Center for Teaching and Learning. Harvard University.

Share this: