Human Memory by Example: Weaknesses

13 minute read

This is part two of “Human Memory By Example.” Last week we focused on strengths of human memory; this week we’ll look at weaknesses with an eye towards how we can mitigate them.

Remembering items without context or understanding

Look at this number for two seconds, close your eyes, and read it back:


Did you get it? Unless you are very good at spotting patterns quickly, you almost certainly couldn’t memorize it that fast. But if you take a closer look, this number is actually the Fibonacci sequence without any spaces in between elements. That is, each number is the sum of the two numbers that came before it: 1 + 1 = 2, 1 + 2 = 3, 2 + 3 = 5, 3 + 5 = 8, 5 + 8 = 13, 8 + 13 = 21, and so on to the end.

Now that you know this piece of context, I bet you could recite the number accurately a week from now (if a bit slowly as you do the math), without spending another second reviewing it! Furthermore, if you know anything about the Fibonacci sequence (or you click the link and read the Wikipedia article), you actually understand what this number means and why it’s interesting.

Don’t waste your time trying to memorize things without understanding what you’re memorizing. Even if you do manage to learn them with great difficulty, the information will be of little to no value.

Reproducing text verbatim

Read the following two paragraphs by G.K. Chesterton (randomly selected from my commonplace file).

In the matter of reforming things, as distinct from deforming them, there is one plain and simple principle; a principle which will probably be called a paradox. There exists in such a case a certain institution or law; let us say, for the sake of simplicity, a fence or gate erected across a road. The more modern type of reformer goes gaily up to it and says, “I don’t see the use of this; let us clear it away.” To which the more intelligent type of reformer will do well to answer: “If you don’t see the use of it, I certainly won’t let you clear it away. Go away and think. Then, when you can come back and tell me that you do see the use of it, I may allow you to destroy it.”

This paradox rests on the most elementary common sense. The gate or fence did not grow there. It was not set up by somnambulists who built it in their sleep. It is highly improbable that it was put there by escaped lunatics who were for some reason loose in the street. Some person had some reason for thinking it would be a good thing for somebody. And until we know what the reason was, we really cannot judge whether the reason was reasonable. It is extremely probable that we have overlooked some whole aspect of the question, if something set up by human beings like ourselves seems to be entirely meaningless and mysterious. There are reformers who get over this difficulty by assuming that all their fathers were fools; but if that be so, we can only say that folly appears to be a hereditary disease. But the truth is that nobody has any business to destroy a social institution until he has really seen it as an historical institution. If he knows how it arose, and what purposes it was supposed to serve, he may really be able to say that they were bad purposes, or that they have since become bad purposes, or that they are purposes which are no longer served. But if he simply stares at the thing as a senseless monstrosity that has somehow sprung up in his path, it is he and not the traditionalist who is suffering from an illusion.

Now, read those two paragraphs back word for word with your eyes closed.

Any luck? Did you get all the words exactly right? Of course you didn’t. Now try this: explain to someone sitting next to you (or to a rubber duck) what Chesterton is saying. This should be much easier, and if you thought this passage was important to remember over a long period of time, you could review your summary periodically and remember that with little trouble.

Centuries ago, before printing became common and books were still extremely expensive, there were many books even the richest and best-educated scholars would get to read only once in their lifetime. When such scholars started writing their own work, they would thus have to quote the previous thinkers from memory. Nobody saw this as remotely problematic, and certainly nobody would have been attacked for misquoting, as long as they had the sense right; everyone’s expectations were just less exact because getting the details perfect would have been such a burden nobody even thought about doing it.

While people don’t try to memorize most texts verbatim nowadays, people often still persist in trying to learn information in needlessly complex ways. If you’re having trouble learning something, take a pause and consider whether you’re trying too hard to memorize something exactly just so when you actually don’t need to remember it that way.

Partial exception. It’s worth pointing out that verse, particularly verse with formal patterns like regular meter and rhyme, is substantially easier to memorize. It’s no accident that the epics we have today that originated before the invention of writing are universally poetry. If you memorize an entire epic, you’ll likely end up dropping or changing some connecting words by mistake, but you can probably get the vast majority of the words right on without too much pain. While I’m not aware of any research on the reasons for this, I presume that the more interest the words themselves provide, the easier it is to remember them; see Remembering unusual ideas, from last week.

Remembering fiddly, small items like numbers

Try memorizing these numbers:

10001101, 110010, 110010101

Now how about these?

141, 50, 405

And how about this?

Turtles are slow.

Here’s the trick: all three of these are representations of exactly the same numbers. The first set is written in binary to be purposefully difficult; the second, medium-difficulty, set uses traditional, base-10 decimal numbers like a phone number or PIN or product code you might want to remember would use; and the third set uses a special mapping designed expressly for memorizing numbers more easily, called the Major System, which we’ll look at in detail in a future post.

Remembering something with poorly spaced rehearsals

Think about a subject you studied in high school or college but haven’t used since. If you’re not an engineer but you did at least okay in math, maybe calculus would be a good example. How much do you still remember about it? Hopefully you remember a broad outline of the subject, and if you suddenly started a new job that required a deep knowledge of it, you would be able to pick it up again in much less time than it took you back then. But you probably don’t remember all the specific tools for, say, evaluating an integral anymore.

Now think about a subject you studied and still think about regularly. You probably remember just about everything that you studied that’s still relevant to you. You probably even remember specific tricks that your teachers taught you.

What’s the difference? That sounds like a dumb question; obviously, the difference is that when it comes to memory, if you don’t use it, you lose it. But more precisely, the difference is that the scheduling of your review is different. In the first example, you may have studied integrals for hours and hours back in school so you could really figure them out. Maybe you spent way more time on them than you’ve spent practicing your English prose, but because your job requires you to write regularly, you’ve kept exercising those skills since you left school.

It turns out that this pattern of review doesn’t just work over timescales of years or decades; it works over months, weeks, and days as well. Studying or practicing something many times in a row yields weaker memories and lower retention than if you space them out over longer periods of time – sometimes even if you end up studying fewer hours overall! This is known as the spacing effect, and taking advantage of the spacing effect is probably the most foundational element of any effective study routine. Strangely, many people – even serious students – still know very little about it except something vague about how they need to review information periodically to remember it. It should not come as a surprise that there will be a future post in this series with details on the spacing effect and how you can take advantage of it.

Remembering something unchanged over long periods

People tend to have especially vivid recollections of distressing events, often known as flashbulb memories. If you’re American and old enough to remember the 9/11 terrorist attacks, do you remember what you were doing when you found out something out of the ordinary happened? (If you don’t have a strong memory of these attacks, pick a different major, distressing event that had a similar impact on you.) Think through your story for a moment.

Guess what: your story is almost certainly wrong! Most people are confident they have it right, but several researchers have studied flashbulb memories by having people write down their story hours after the event, then return some months or years later and repeat their story. In actuality, the stories are almost never the same, and the later stories often bear little resemblance at all to the original accounts. Here’s an example from a study on the Challenger explosion, accessible from the article I linked above:

“When I first heard about the explosion I was sitting in my freshman dorm room with my roommate and we were watching TV,” wrote an Emory University student who participated in a memory study a year and a half after the Challenger disaster. “It came on as a news flash and we were both totally shocked.”

But that same student had given a surprisingly different answer, just 24 hours after the tragedy. “I was in my religion class and some people walked in and started talking about [it],” she wrote. “I didn’t know any details except that it had exploded and the schoolteacher’s students had all been watching which I thought was so sad.”

If you want to finish out the example, grab someone who was with you or heard your story shortly after the event. Is their recollection the same?

The discrepancy between people’s confidence and the actual fidelity of their memories is very dramatic in flashbulb memories, but certainly all autobiographical memories and many other kinds of memories are subject to the same effect. I bet you can think of some other moments, even off the top of your head, when you were quite sure you remembered something accurately but you turned out to be wrong.

I’m not aware of any tricks for fixing this basic limitation of human memory. The only reliable way to mitigate this issue is by promptly writing down things you want to remember accurately that would otherwise be stored only in your memory – say, in a journal. Unless you lose the notebook, what you wrote down on paper won’t change.

Accessing information in slightly different ways than usual

Have you ever looked right at someone you knew and not recognized them? I was once at breakfast at a restaurant with my uncle. He had eaten breakfast at this restaurant every Friday morning for several years, like clockwork, always being served by the same waitress and ordering the same thing, but when she walked up to our table to take our drink orders, she didn’t recognize him! She didn’t recognize him because he was sitting at a different table with different people – just enough out of context to throw her off.

How many times have you walked into a room and then stood there blankly, trying to remember why you went there? You probably know that if you walk back to where you were when you decided to go, you’ll often remember what you were intending to do. This is the same principle in action: when you return to your original location, you restore your original context and can access the information the same way you originally did.

Because we always access information by associating it with other information, it’s easy to run into this issue if we associate it (usually accidentally) with a very specific set of other information that isn’t always available when we need to recall the target information. This can be particularly dangerous when studying from books or flashcards; you can unintentionally pick up on details like errors in your handwriting or the exact way a question is phrased and fail to learn the underlying concepts properly. We’ll look at ways to combat this in a future post.

Avoiding confusion between similar items

How many times have you seen someone write they’re instead of their? Do you remember the difference between effect and affect without stopping to think about it? How about ensure and insure?

The campus of Valparaiso University used to have buildings named Meier, Mueller, and Miller. Guess how often people new to campus showed up at one on the wrong end of campus? (Thankfully, one of them has been demolished, so it’s not quite so bad as it once was.)

If you don’t live on the East Coast of the United States, can you identify each of the small states in the New England area on an unlabeled map? Because they’re small and have few distinguishing stereotypes known to people from outside the area, people from other regions who otherwise have decent knowledge of U.S. geography often can’t keep them straight.

Good design strives to avoid confusing similarities between items because people are naturally bad at sorting them out. Unfortunately, nobody is about to redesign the English language for us, and we will never stop coming up with new bad designs, so we’re forced to deal with them on occasion. Sorting out confusing pairs (or triples!) requires careful attention and persistence. We’ll discuss some techniques in a future post.