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Chapter Two
The Power of Forgetting
A New Theory of Learning
Memory contests are misleading spectacles, especially in the final rounds.
At that point, there are only a handful of people left onstage and their faces reflect all varieties of exhaustion, terror, and concentration. The stakes are high, they’ve come a long way already, and any mistake can end it all. In a particularly tough to watch scene from the documentary Spellbound, about the Scripps National Spelling Bee, one twelve-year-old trips over the word “opsimath.” He appears to be familiar with the word, he’s digging deep, there’s a moment when he seems to have it—but then he inserts an “o” where it doesn’t belong.
Clang!
A bell rings—meaning: wrong answer—and the boy’s eyes bulge in stunned disbelief. A gasp sweeps through the crowd, followed by clapping, consolation applause for effort. He slinks offstage, numb. Variations of this scene repeat, as other well-prepped contestants miss a word. They slump at the microphone, or blink without seeing, before being bathed in the same lukewarm applause. In contrast, those who move to the next round seem confident, locked in. The winner smiles when she hears her final word—“logorrhea”—and nails it.
These competitions tend to leave us with two impressions. One is that the contestants, and especially the winners, must be extra-human. How on earth are they doing that? Their brains must be not only bigger and faster but also different from the standard-issue version (i.e., ours). Maybe they even have “photographic” memories.
Not so. Yes, it’s true that some people are born with genetic advantages, in memory capacity and processing speed (though no one has yet identified an “intelligence gene” or knows with any certainty how one would function). It’s true, too, that these kinds of contests tend to draw from the higher end of the spectrum, from people who take a nerdy interest in stockpiling facts. Still, a brain is a brain is a brain, and the healthy ones all work the same way. With enough preparation and devotion, each is capable of seemingly wizardlike feats of memory. And photographic memories, as far as scientists can tell, don’t exist, at least not in the way that we imagine.
The other impression is more insidious, because it reinforces a common, self-defeating assumption: To forget is to fail. This appears self-evident. The world is so full of absentmindedness, tuned-out teenagers, misplaced keys, and fear of creeping dementia that forgetting feels dysfunctional, or ominous. If learning is building up skills and knowledge, then forgetting is losing some of what was gained. It seems like the enemy of learning.
It’s not. The truth is nearly the opposite.
Of course it can be a disaster to space out on a daughter’s birthday, to forget which trail leads back to the cabin, or to draw a blank at test time. Yet there are large upsides to forgetting, too. One is that it is nature’s most sophisticated spam filter. It’s what allows the brain to focus, enabling sought-after facts to pop to mind.
One way to dramatize this would be to parade all those spelling prodigies back onstage again for another kind of competition, a fast-paced tournament of the obvious. Quick: Name the last book you read. The last movie you saw. The local drugstore. The secretary of state. The World Series champions. And then faster still: your Gmail password, your sister’s middle name, the vice president of the United States.
In this hypothetical contest, each of those highly concentrated minds would be drawing a lot of blanks. Why? Not due to mere absentmindedness or preoccupation. No, these kids are alert and highly focused. So focused, in fact, that they’re blocking out trivial information.
Think about it: To hold so many obscure words in mind and keep the spellings straight, the brain must apply a filter. To say it another way, the brain must suppress—forget—competing information, so that “apathetic” doesn’t leak into “apothecary,” or “penumbra” into “penultimate,” and keep any distracting trivia from bubbling to the surface, whether song lyrics, book titles, or names of movie actors.
We engage in this kind of focused forgetting all the time, without giving it much thought. To lock in a new computer password, for example, we must block the old one from coming to mind; to absorb a new language, we must hold off the corresponding words in our native tongue. When thoroughly immersed in a topic or novel or computation, it’s natural to blank on even common nouns—“could you pass me the whatyoucallit, the thing you eat with?”
Fork.
As the nineteenth-century American psychologist William James observed, “If we remembered everything, we should on most occasions be as ill off as if we remembered nothing.”
The study of forgetting has, in the past few decades, forced a fundamental reconsideration of how learning works. In a way, it has also altered what the words “remember” and “forget” mean. “The relationship between learning and forgetting is not so simple and in certain important respects is quite the opposite of what people assume,” Robert Bjork, a psychologist at the University of California, Los Angeles, told me. “We assume it’s all bad, a failure of the system. But more often, forgetting is a friend to learning.”
The “losers” in memory competitions, this research suggests, stumble not because they remember too little. They have studied tens, perhaps hundreds of thousands of words, and often they are familiar with the word they ultimately misspell. In many cases, they stumble because they remember too much. If recollecting is just that—a re-collection of perceptions, facts, and ideas scattered in intertwining neural networks in the dark storm of the brain—then forgetting acts to block the background noise, the static, so that the right signals stand out. The sharpness of the one depends on the strength of the other.
Another large upside of forgetting has nothing to do with its active filtering property. Normal forgetting—that passive decay we so often bemoan—is also helpful for subsequent learning. I think of this as the muscle-building property of forgetting: Some “breakdown” must occur for us to strengthen learning when we revisit the material. Without a little forgetting, you get no benefit from further study. It is what allows learning to build, like an exercised muscle.
This system is far from perfect. We have instantaneous and flawless recall of many isolated facts, it’s true: Seoul is the capital of South Korea, 3 is the square root of 9, and J. K. Rowling is the author of the Harry Potter books. Yet no complex memory comes back exactly the same way twice, in part because the forgetting filter blocks some relevant details along with many irrelevant ones. Features that previously were blocked or forgotten often reemerge. This drift in memory is perhaps most obvious when it comes to the sort of childhood tales we all tell and embellish. The time we borrowed the family car at age fourteen; the time we got lost on the metro the first time we visited the city. After rolling out those yarns enough times, it can be tough to tell what’s true and what’s not.
The point is not that memory is nothing more than a pile of loose facts and a catalog of tall tales. It’s that retrieving any memory alters its accessibility, and often its content.
There is an emerging theory that accounts for these and related ideas. It’s called the New Theory of Disuse, to distinguish it from an older, outdated principle stating, simply, that memories evaporate entirely from the brain over time if they’re not used. The new theory is far more than an updating, though. It’s an overhaul, recasting forgetting as the best friend of learning, rather than its rival.
A better name for it, then, might be the Forget to Learn theory. That phrase captures its literal implications and its general spirit, its reassuring voice. One implication, for instance, is that forgetting a huge chunk of what we’ve just learned, especially when it’s a brand-new topic, is not necessarily evidence of laziness, attention deficits, or a faulty character. On the contrary, it is a sign that the brain is working as it should.
No one knows why we should be such poor judges of forgetting or other mental skills that are so indispensable, so automatic, that they feel deeply familiar. Yet we are. And it helps to count the ways.
• • •
Let’s go back to the beginning, then. Let’s go back to the first learning laboratory of them all, to its sole occupant, and his most important contribution—the Forgetting Curve. The Forgetting Curve is exactly what it sounds like, a graph of memory loss over time. In particular, it charts the rate at which newly learned information fades from memory. It’s a learning curve, turned upside-down:
This curve, first published in the late 1880s, falls well short of breathtaking. It’s what anyone might draw if asked to guess how memory changes with time. Yet its creator, Hermann Ebbinghaus, wasn’t one for idle guesswork. He was exacting by nature, compulsive about evidence. He had to be, given his ambitions. In the late 1870s, as a young philosophy Ph.D., he zigzagged through Europe, thinking big. He longed to bridge philosophy and science, to apply rigorous measurement to some aspect of human nature or psychology. The only problem was, he didn’t know where to start. He was poking around in a secondhand Paris bookstall one afternoon when he pulled from the shelf a volume called Elements of Psychophysics by Gustav Fechner. A scientist with a mystical bent, Fechner saw a unifying mathematical connection between the inner, mental world and the outer, natural one. He argued that every human experience, even one as ephemeral as memory, should be reducible to measurable units that could be plugged into an equation of some sort. Fechner’s reputation as a scientist—he’d done elegant experiments on the sensation of touch—lent his more grandiose ideas some weight.
As he read, Ebbinghaus felt something inside him shift—a sensation he would describe, years later, to a student. He must have glimpsed his future as well, right then and there, because he later dedicated his greatest work, Memory: A Contribution to Experimental Psychology, to Fechner.
The memory equation. Did it even exist? If so, could it be written down?
Memories come in so many shapes and sizes. There are the hour-long and the lifelong; there are dates and numbers, recipes and recitals; not to mention stories, emotional perceptions, the look on a child’s face when he’s dropped at the bus stop on the first day of school, the knowing smile shared between two friends who think no one is looking: the tapestry of hijinks and heartbreaks that make up a life. Our ability to recall specific facts also varies widely. Some people are good with names and faces; others are much better at retrieving numbers, dates, formulas. How on earth do you measure such a shape-shifting ghost, much less study it?
A generation of scientists before Ebbinghaus had essentially stood down, taking a pass on the question. It was too much. The variables were overwhelming.
Yet where some saw a justified caution, Ebbinghaus saw a lack of nerve. “At the very worst we should prefer to see resignation arise from the failure of earnest investigations rather than from the persistent, helpless astonishment in the face of the difficulties,” he wrote, in explaining his motives for pursuing the memory equation. He would take the dare if there was no one else. He reasoned from first principles. To study how the brain stores new information, he needed information that was, in fact, new. A list of nouns or names or numbers simply wouldn’t do; people walk around with an enormous storehouse of associations for all of these things. Even abstract sketches have a Rorschach-like, evocative quality. Stare long enough at a cloud and it begins to look like a dog’s head, which in turn activates hundreds of dog-related circuits in the brain. Our brain can impute meaning to almost anything.
How Ebbinghaus arrived at his solution remains a mystery. “Was it an invention in the commonly accepted sense of the term, that is to say, deliberate?” wrote the American psychologist David Shakow, much later, in a biographical essay. “Or was it largely a discovery? What part did the gurgle of an infant, a transient progression to infancy, the reading of Jabberwocky, the expletives of the Paris coachman for the London cabbie, play?”
What Ebbinghaus created was a catalog of nonsense sounds. These were single syllables, formed by sticking a vowel between two consonants. RUR, HAL, MEK, BES, SOK, DUS. By and large, they were meaningless.
Ebbinghaus had found his generic memory “units.”
He created about 2,300 of them—a pool of all possible syllables, or at least as many as he could think of. He put together lists of the syllables, random groupings of between seven and thirty-six each. Then he began to memorize one list at a time, reading the syllables out loud, pacing himself with a metronome, keeping track of how many repetitions he needed to produce a perfect score.
By the time he landed a job as an instructor, at the University of Berlin in 1880, he’d logged more than eight hundred hours of practice with his nonsense sounds. He continued the work in his small office, pacing the floor, a compact, bushy-bearded man in Ben Franklin spectacles, spitting out the syllables at a rate of as many as 150 a minute. (In another era or another country, he might have been hauled off and fitted with a lunatic suit.) He tested himself at various intervals: Twenty minutes after studying. An hour. A day later, then a week. He varied the duration of his practice sessions, too, and found (surprise) that more practice sessions generally resulted in higher test scores and a slower rate of forgetting.
In 1885, he published his results in Memory: A Contribution to Experimental Psychology, describing a simple way to calculate the rate of forgetting after a study session. The equation wasn’t much to look at, but it was the first rigorous principle in the emerging branch of psychology—and precisely what he’d set out to find a decade earlier in that Paris bookstall.
Ebbinghaus had his equation (others would plot it as a graph).
He hadn’t changed the world. He did, however, launch the science of learning. “It is not too much to say that the recourse to nonsense syllables, as a means to the study of association, marks the most considerable advance in this chapter of psychology since the time of Aristotle,” wrote English scientist Edward Titchener a generation later.
Ebbinghaus’s Forgetting Curve captured the minds of many theorists and would not let go. In 1914, the influential American education researcher Edward Thorndike turned Ebbinghaus’s curve into a “law” of learning. He called it the Law of Disuse, which asserted that learned information, without continued use, decays from memory entirely—i.e., use it or lose it.
The law felt right. It certainly seemed to square with experience, defining how most people thought of learning and to this day still do. Yet that definition hides more than it reveals.
• • •
Here’s an at-home exercise that is simple, painless, and full of literary nutrition. Take five minutes and study the verse below. Read it carefully and try to commit it to memory. It’s from the poet Henry Wadsworth Longfellow’s “The Wreck of the Hesperus.”
At daybreak, on the bleak sea-beach,
A fisherman stood aghast,
To see the form of a maiden fair,
Lashed close to a drifting mast.
The salt sea was frozen on her breast,
The salt tears in her eyes;
And he saw her hair, like the brown sea-weed,
On the billows fall and rise.
Such was the wreck of the Hesperus,
In the midnight and the snow!
Christ save us all from a death like this,
On the reef of Norman’s Woe!
Okay, now put the book aside and make a cup of coffee, take a walk, listen to the news. Distract yourself for about five minutes, the same amount of time you took to study it. Then, sit and write down as much of the poem as you can. Save the result (you’ll need it later).
This is exactly the test that an English teacher and researcher named Philip Boswood Ballard began administering to schoolchildren in the early 1900s in London’s working-class East End. The children were thought to be poor learners, and Ballard was curious to find out why. Was it a deficit of initial learning? Or did something happen later that interfered with recall? To find out, he had them study various material, including ballads like Longfellow’s, to see if he could pinpoint the source of their learning problems.
Only the children had no obvious learning deficits that Ballard could find. On the contrary.
Their scores five minutes after studying were nothing special. Some did well and others didn’t. Ballard wasn’t finished, however. He wanted to know what happened to the studied verse over time. Did memory somehow falter in the days after these children studied? To find out, he gave them another test, two days later. The students were not expecting to be retested and yet their scores improved by an average of 10 percent. Ballard tested them once more, again unannounced, days later.
“J.T. improved from 15 to 21 lines in three days,” he wrote of one student. “Imagined she saw the lines in front of her.” Of another, who improved from three to eleven lines in seven days, he remarked: “Pictured the words on the blackboard (the poetry in this case was learnt from the blackboard).” A third, who recalled nine lines on the first test and, days later, thirteen, told Ballard, “as I began to write it, I could picture it on the paper before me.”
This improvement wasn’t merely odd. It was a flat contradiction of Ebbinghaus.
Ballard doubted what he was seeing and ran hundreds of additional tests, with more than ten thousand subjects, over the next several years. The results were the same: Memory improved in the first few days without any further study, and only began to taper off after day four or so, on average.
Ballard reported his findings in 1913, in a paper that seems to have caused mostly confusion. Few scientists appreciated what he’d done, and even today he is little more than a footnote in psychology, a far more obscure figure than Ebbinghaus. Still, Ballard knew what he had. “We not only tend to forget what we have once remembered,” he wrote, “but we also tend to remember what we have once forgotten.”
Memory does not have just one tendency over time, toward decay. It has two.
The other—“reminiscence,” Ballard called it—is a kind of growth, a bubbling up of facts or words that we don’t recall having learned in the first place. Both tendencies occur in the days after we’ve tried to memorize a poem or a list of words.
What could possibly be going on?
One clue comes from Ebbinghaus. He had tested memory using only nonsense syllables. The brain has no place to “put” these letter trios. They’re not related to one another or to anything else; they’re not part of a structured language or pattern. The brain doesn’t hold on to nonsense syllables for long, then, because they are nonsense. Ebbinghaus acknowledged as much himself, writing that his famous curve might not apply to anything more than what he had studied directly.
Forgetting, remember, is not only a passive process of decay but also an active one, of filtering. It works to block distracting information, to clear away useless clutter. Nonsense syllables are clutter; Longfellow’s “The Wreck of the Hesperus” is not. The poem may or may not become useful in our daily life, but at least it is nested in a mesh of neural networks representing words and patterns we recognize. That could account for why there would be a difference in how well we remember nonsense syllables versus a poem, a short story, or other material that makes sense. Yet it does not explain the increase in clarity after two days without rehearsal, the “salt tears” and “hair like brown sea-weed” floating up from the neural deep. Those “slow” East Enders showed Ballard that remembering and forgetting are not related to each other in the way everyone assumed.
The Forgetting Curve was misleading and, at best, incomplete. It might even need to be replaced altogether.
• • •
In the decades after Ballard published his findings, there was a modest flare of interest in “spontaneous improvement.” The effect should be easy to find, scientists reasoned, in all kinds of learning. Yet it wasn’t. Researchers ran scores of experiments, and the results were all over the place. In one huge 1924 trial, for instance, people studied a word list, and took a test immediately afterward. They were then given a follow-up test, after varying delays: eight minutes, sixteen minutes, three days, a week. They did worse over time, on average, not better.
In a 1937 experiment, subjects who studied nonsense syllables showed some spontaneous improvement after an initial exam—but only for about five minutes, after which their scores plunged. A widely cited 1940 study found that people’s recall of a set of words, a set of brief sentences, and a paragraph of prose all declined over a twenty-four-hour period. Even when researchers found improvement for one kind of material, like poetry, they’d find the opposite result for something else, like vocabulary lists. “Experimental psychologists began to tinker with Ballard’s approach and, as if struggling in quicksand, became progressively mired in confusion and doubt,” wrote Matthew Hugh Erdelyi, of Brooklyn College, in his history of the era, The Recovery of Unconscious Memories.
The mixed findings inevitably led to questions about Ballard’s methods. Were the children he tested really recalling more over time, or was their improvement due to some flaw in the experimental design? It wasn’t a rhetorical question. What if, for example, the children had rehearsed the poem on their own time, between tests? In that case, Ballard had nothing.
In an influential review of all published research up through 1943, one British learning theorist, C. E. Buxton, concluded that Ballard’s spontaneous improvement effect was a “now-you-see-it-now-you-don’t phenomenon”—in other words, a phantom. It wasn’t long before many scientists followed Buxton’s lead and begged off the hunt. There were far better things to do with the tools of psychology than chase phantoms, and certainly more culturally fashionable ones.
Freudian therapy was on the rise, and its ideas of recovered memories easily trumped Ballard’s scraps of Longfellow for sex appeal. The two men’s conceptions of recovery were virtually identical, except that Freud was talking about repressed emotional trauma. Excavating those memories and “working through” them could relieve chronic, disabling anxiety, he claimed. It could change lives. If those were phantoms, they were far more lifelike than a heap of recited poetry.
Besides, the real juice in learning science by the middle of the century was in reinforcement. It was the high summer of behaviorism. The American psychologist B. F. Skinner showed how rewards and punishments could alter behavior, and accelerate learning in many circumstances. Skinner tested various reward schedules against one another and got striking results: An automatic reward for a correct answer leads to little learning; occasional, periodic rewards are much more effective. Skinner’s work, which was enormously influential among educators, focused on improving teaching, rather than on the peculiarities of memory.
Yet Ballard’s findings didn’t disappear completely. They continued to marinate in the minds of a small group of psychologists who couldn’t shake the idea that something consequential might be slipping through the cracks. In the 1960s and 1970s, these curious few began to separate the poetry from the nonsense.
The Ballard effect was, and is, real. It was not due to an experimental design flaw; the children in his studies could not have rehearsed lines that they did not remember after the first test. You can’t practice what you don’t remember. The reason researchers had had so much trouble isolating Ballard’s “reminiscence” was because the strength of this effect is highly dependent on the material being used. For nonsense syllables, and for most lists of vocabulary words or random sentences, it’s zero: There’s no spontaneous improvement on test scores after a day or two. By contrast, reminiscence is strong for imagery, for photographs, drawings, paintings—and poetry, with its word-pictures. And it takes time to happen. Ballard had identified the “bubbling up” of new verse in the first few days after study, when it’s strongest. Other researchers had looked for it too early, minutes afterward, or too late, after a week or more.
Matthew Erdelyi was one of those who was instrumental in clarifying reminiscence, and he began by testing a junior colleague, Jeff Kleinbard, then at Stanford University. Erdelyi gave Kleinbard a group of forty pictures to study in a single sitting, on the pretext that he “should have the experience of being a subject” before conducting experiments of his own. In fact, he was a subject, and Erdelyi tested him repeatedly, without warning, over the following week. The results were so clear and reliable—Kleinbard remembered increasingly more on tests over the first two days—that the two of them set up larger studies. In one, they had a group of young adults try to memorize a series of sixty sketches. The participants saw the sketches one at a time, projected on a screen, five seconds apart: simple drawings of things like a boot, a chair, a television.
The group took a test right after and tried to recall all sixty, in seven minutes, writing down a word to describe each sketch recalled (the sketches had no accompanying words). The average score was 27. Ten hours later, however, their average was 32; a day later, 34; by four days, it was up to 38, where it plateaued. A comparison group, who studied sixty words presented on slides, improved from 27 to 30 in the first ten hours—and no more. Their scores slipped slightly over the next several days. Soon it was beyond dispute that memory, as Erdelyi put it in a recent paper, “is a heterogeneous, mottled system that both improves and declines over time.”
Which left theorists with a larger riddle. Why does recall of pictures improve while recall of word lists does not?
Scientists had speculated about the answers all along. Maybe it was a matter of having more time to search memory (two tests versus one). Or perhaps the delay between tests relaxed the mind, eased fatigue. Yet it wasn’t until the 1980s that psychologists had enough hard evidence to begin building a more complete model that accounts for the Ballard effect and other peculiarities of memory. The theory that emerged is less a grand blueprint for how the mind works than a set of principles based on research, a theory that encompasses Ebbinghaus and Ballard, as well as many other seemingly opposed ideas and characters. The scientists who have shepherded the theory along and characterized it most clearly are Robert Bjork of UCLA and his wife, Elizabeth Ligon Bjork, also at UCLA. The new theory of disuse (“Forget to Learn,” as we’re calling it) is largely their baby.
The first principle theory is this: 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. The multiplication table is a good example. It’s drilled into our heads in grade school, and we use it continually throughout life, in a wide variety of situations, from balancing the bank account to calculating tips to helping our fourth grader with homework. Its storage strength is enormous.
According to the Bjorks’ theory, storage strength can increase but it never decreases.
This does not mean that everything we see, hear, or say is stored forever, until we die. More than 99 percent of experience is fleeting, here and gone. The brain holds on to only what’s relevant, useful, or interesting—or may be so in the future. It does mean that everything we have deliberately committed to memory—the multiplication table, a childhood phone number, the combination to our first locker—is all there, and for good. This seems beyond belief at first, given the sheer volume of information we absorb and how mundane so much of it is. Remember from chapter 1, though, that biologically speaking there’s space to burn: in digital terms, storage space for three million TV shows. That is more than enough to record every second of a long life, cradle to grave. Volume is not an issue.
As for the mundane, it’s impossible to prove that it’s all there, every meaningless detail. Still, every once in a while the brain sends up a whisper of dumbfounding trivia. It happens to everyone throughout life; I’ll offer an example of my own. In researching this book, I spent some time in college libraries, the old-school kind, with basements and subbasements full of stacks of old books that create the vague sensation of being on an archaeological dig. It was the musty smell, I think, that on one afternoon took me back to a month-long period in 1982 when I worked at my college library. I was hunting down an old book in some deserted corner of the Columbia University library, feeling claustrophobic and lost—when a name popped into my head. Larry C______. The name of the man at the library who was (I guess) my supervisor. I met him once. Lovely guy—only I had no idea I ever knew his name. Still, here I was, seeing him in my mind’s eye walking away from that one meeting, and even seeing that his boat shoes were worn in the back the way some people’s get, angling toward one another.
One meeting. The shoes. Perfectly meaningless. Yet I must have known the name, and I must have stored that impression of him walking off. Why on earth would I have kept that information? Because it was, at one point in my life, useful. And the Forget to Learn theory says: If I stored it, it’s in there for good.
That is, no memory is ever “lost” in the sense that it’s faded away, that it’s gone. Rather, it is not currently accessible. Its retrieval strength is low, or near zero.
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, and its capacity is relatively small (compared to storage). At any given time, we can pull up only a limited number of items in connection with any given cue or reminder.
For example, a quack-quack cell phone ring overheard on the bus might bring to mind the name of a friend who has the same ring, as well as several people who are owed calls. It may also trigger an older vision of the family dog belly-flopping into a lake to pursue a flotilla of ducks; or your first raincoat, bright yellow with a duckbill on the hood. Thousands of other quack associations, some meaningful at the time they formed, are entirely off the radar.
Compared to storage, retrieval strength is fickle. It can build quickly but also weaken quickly.
One way to think of storage and retrieval is to picture a huge party in which everyone you ever met is in attendance (at the age when you last saw them). Mom and Dad; your first grade teacher; the brand-new neighbors next door; the guy who taught driver’s-ed in sophomore year: They’re all here, mingling. Retrieval is a matter of how quickly a person’s name comes to mind. Storage, by contrast, is a matter of how familiar the person is. Mom and Dad, there’s no escaping them (retrieval high, storage high). The first grade teacher, her name isn’t jumping to mind (retrieval low) but that’s definitely her right there over by the door (storage high). The new neighbors, by contrast, just introduced themselves (“Justin and Maria”—retrieval high), but they’re not familiar yet (storage low). Tomorrow morning, their names will be harder to recall. As for the driver’s-ed guy, the name’s not coming back, and he wouldn’t be so easy to pick out of a lineup, either. The class was only two months long (retrieval low, storage low).
The act of finding and naming each person increases both strengths, remember. The first grade teacher—once she’s reintroduced—is now highly retrievable. This is due to the passive side of forgetting, the fading of retrieval strength over time. The theory says that that drop facilitates deeper learning once the fact or memory is found again. Again, think of this aspect of the Forget to Learn theory in terms of building muscle. Doing pull-ups induces tissue breakdown in muscles that, after a day’s rest, leads to more strength the next time you do the exercise.
That’s not all. The harder we have to work to retrieve a memory, the greater the subsequent spike in retrieval and storage strength (learning). The Bjorks call this principle desirable difficulty, and its importance will become apparent in the coming pages. That driver’s-ed teacher, once he’s spotted, is now way more familiar than he was before, and you may remember things about him you forgot you knew: not just his name and nickname but his crooked smile, his favorite phrases.
The brain developed this system for a good reason, the Bjorks argue. 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.
This combination of flighty retrieval and steady storage—the tortoise and the hare—is no less important to modern-day survival. Kids who grow up in North American households, for example, learn to look people in the eye when speaking, especially a teacher or parent. Kids in Japanese homes learn the opposite: Keep your gaze down, especially when speaking to an authority figure. To move successfully from one culture to the other, people must block—or forget—their native customs to quickly absorb and practice the new ones. The native ways are hardly forgotten; their storage strength is high. But blocking them to transition to a new culture drives down their retrieval strength.
And being able to do this can be a matter of life or death. An Australian who moves to the United States, for instance, must learn to drive on the right side of the road instead of the left, upending almost every driving instinct he has. There’s little room for error; one Melbourne daydream and he wakes up in a ditch. Here again, the memory system forgets all the old instincts to make room for the new ones. And that’s not all. If twenty years later he gets homesick and moves back to Australia, he will have to switch to driving on the left again. Yet that change will come much more easily than the first one did. The old instincts are still there, and their storage strength is still high. The old dog quickly relearns old tricks.
“Compared to some kind of system in which out-of-date memories were to be overwritten or erased,” Bjork writes, “having such memories become inaccessible but remain in storage has important advantages. Because those memories are inaccessible, they don’t interfere with current information and procedures. But because they remain in memory they can—at least under certain circumstances—be relearned.”
Thus, forgetting is critical to the learning of new skills and to the preservation and reacquisition of old ones.
Now let’s return to our friend Philip Ballard. The first test his students took not only measured how much of the “Hesperus” poem they remembered. It also increased the storage and retrieval strengths of the verse they did remember, making it more firmly anchored in memory and more easily accessible than it was before the test. Hit, unexpectedly, with the same test two days later, most of the lines they recalled on test number 1 came back clearly and quickly—and as a result, their brains had time to scrounge for more words, using the remembered verse as a skeleton guide, a partially completed jigsaw puzzle, a packet of cues to shake loose extra lines. This is a poem, after all, swollen with imagery and meaning, precisely the material that shows the strongest “reminiscence” effect of all.
Voilà! They do better.
Yes, the Hesperus will eventually sink if the brain stops thinking about it, and its retrieval strength will inch toward zero. But a third test, and a fourth, would anchor the poem in memory more richly still, as the brain—now being called on to use the poem regularly—would continue its search for patterns within the poem, perhaps pulling up another half line or two with each exam. Will it all come back, with enough testing, even if only half was remembered the first time? Not likely. You get something back, not everything.
Try it yourself, after a day or two. Write down as much of the “The Wreck of the Hesperus” as you can, without looking. Give yourself as much time as you took on the first test at the top of the chapter. Compare the results. If you’re like most people, you did a little better on the second test.
Using memory changes memory—and for the better. Forgetting enables and deepens learning, by filtering out distracting information and by allowing some breakdown that, after reuse, drives retrieval and storage strength higher than they were originally. Those are the basic principles that emerge from brain biology and cognitive science, and they underlie—and will help us understand—the various learning techniques yet to come.
The Power of Forgetting
A New Theory of Learning
Memory contests are misleading spectacles, especially in the final rounds.
At that point, there are only a handful of people left onstage and their faces reflect all varieties of exhaustion, terror, and concentration. The stakes are high, they’ve come a long way already, and any mistake can end it all. In a particularly tough to watch scene from the documentary Spellbound, about the Scripps National Spelling Bee, one twelve-year-old trips over the word “opsimath.” He appears to be familiar with the word, he’s digging deep, there’s a moment when he seems to have it—but then he inserts an “o” where it doesn’t belong.
Clang!
A bell rings—meaning: wrong answer—and the boy’s eyes bulge in stunned disbelief. A gasp sweeps through the crowd, followed by clapping, consolation applause for effort. He slinks offstage, numb. Variations of this scene repeat, as other well-prepped contestants miss a word. They slump at the microphone, or blink without seeing, before being bathed in the same lukewarm applause. In contrast, those who move to the next round seem confident, locked in. The winner smiles when she hears her final word—“logorrhea”—and nails it.
These competitions tend to leave us with two impressions. One is that the contestants, and especially the winners, must be extra-human. How on earth are they doing that? Their brains must be not only bigger and faster but also different from the standard-issue version (i.e., ours). Maybe they even have “photographic” memories.
Not so. Yes, it’s true that some people are born with genetic advantages, in memory capacity and processing speed (though no one has yet identified an “intelligence gene” or knows with any certainty how one would function). It’s true, too, that these kinds of contests tend to draw from the higher end of the spectrum, from people who take a nerdy interest in stockpiling facts. Still, a brain is a brain is a brain, and the healthy ones all work the same way. With enough preparation and devotion, each is capable of seemingly wizardlike feats of memory. And photographic memories, as far as scientists can tell, don’t exist, at least not in the way that we imagine.
The other impression is more insidious, because it reinforces a common, self-defeating assumption: To forget is to fail. This appears self-evident. The world is so full of absentmindedness, tuned-out teenagers, misplaced keys, and fear of creeping dementia that forgetting feels dysfunctional, or ominous. If learning is building up skills and knowledge, then forgetting is losing some of what was gained. It seems like the enemy of learning.
It’s not. The truth is nearly the opposite.
Of course it can be a disaster to space out on a daughter’s birthday, to forget which trail leads back to the cabin, or to draw a blank at test time. Yet there are large upsides to forgetting, too. One is that it is nature’s most sophisticated spam filter. It’s what allows the brain to focus, enabling sought-after facts to pop to mind.
One way to dramatize this would be to parade all those spelling prodigies back onstage again for another kind of competition, a fast-paced tournament of the obvious. Quick: Name the last book you read. The last movie you saw. The local drugstore. The secretary of state. The World Series champions. And then faster still: your Gmail password, your sister’s middle name, the vice president of the United States.
In this hypothetical contest, each of those highly concentrated minds would be drawing a lot of blanks. Why? Not due to mere absentmindedness or preoccupation. No, these kids are alert and highly focused. So focused, in fact, that they’re blocking out trivial information.
Think about it: To hold so many obscure words in mind and keep the spellings straight, the brain must apply a filter. To say it another way, the brain must suppress—forget—competing information, so that “apathetic” doesn’t leak into “apothecary,” or “penumbra” into “penultimate,” and keep any distracting trivia from bubbling to the surface, whether song lyrics, book titles, or names of movie actors.
We engage in this kind of focused forgetting all the time, without giving it much thought. To lock in a new computer password, for example, we must block the old one from coming to mind; to absorb a new language, we must hold off the corresponding words in our native tongue. When thoroughly immersed in a topic or novel or computation, it’s natural to blank on even common nouns—“could you pass me the whatyoucallit, the thing you eat with?”
Fork.
As the nineteenth-century American psychologist William James observed, “If we remembered everything, we should on most occasions be as ill off as if we remembered nothing.”
The study of forgetting has, in the past few decades, forced a fundamental reconsideration of how learning works. In a way, it has also altered what the words “remember” and “forget” mean. “The relationship between learning and forgetting is not so simple and in certain important respects is quite the opposite of what people assume,” Robert Bjork, a psychologist at the University of California, Los Angeles, told me. “We assume it’s all bad, a failure of the system. But more often, forgetting is a friend to learning.”
The “losers” in memory competitions, this research suggests, stumble not because they remember too little. They have studied tens, perhaps hundreds of thousands of words, and often they are familiar with the word they ultimately misspell. In many cases, they stumble because they remember too much. If recollecting is just that—a re-collection of perceptions, facts, and ideas scattered in intertwining neural networks in the dark storm of the brain—then forgetting acts to block the background noise, the static, so that the right signals stand out. The sharpness of the one depends on the strength of the other.
Another large upside of forgetting has nothing to do with its active filtering property. Normal forgetting—that passive decay we so often bemoan—is also helpful for subsequent learning. I think of this as the muscle-building property of forgetting: Some “breakdown” must occur for us to strengthen learning when we revisit the material. Without a little forgetting, you get no benefit from further study. It is what allows learning to build, like an exercised muscle.
This system is far from perfect. We have instantaneous and flawless recall of many isolated facts, it’s true: Seoul is the capital of South Korea, 3 is the square root of 9, and J. K. Rowling is the author of the Harry Potter books. Yet no complex memory comes back exactly the same way twice, in part because the forgetting filter blocks some relevant details along with many irrelevant ones. Features that previously were blocked or forgotten often reemerge. This drift in memory is perhaps most obvious when it comes to the sort of childhood tales we all tell and embellish. The time we borrowed the family car at age fourteen; the time we got lost on the metro the first time we visited the city. After rolling out those yarns enough times, it can be tough to tell what’s true and what’s not.
The point is not that memory is nothing more than a pile of loose facts and a catalog of tall tales. It’s that retrieving any memory alters its accessibility, and often its content.
There is an emerging theory that accounts for these and related ideas. It’s called the New Theory of Disuse, to distinguish it from an older, outdated principle stating, simply, that memories evaporate entirely from the brain over time if they’re not used. The new theory is far more than an updating, though. It’s an overhaul, recasting forgetting as the best friend of learning, rather than its rival.
A better name for it, then, might be the Forget to Learn theory. That phrase captures its literal implications and its general spirit, its reassuring voice. One implication, for instance, is that forgetting a huge chunk of what we’ve just learned, especially when it’s a brand-new topic, is not necessarily evidence of laziness, attention deficits, or a faulty character. On the contrary, it is a sign that the brain is working as it should.
No one knows why we should be such poor judges of forgetting or other mental skills that are so indispensable, so automatic, that they feel deeply familiar. Yet we are. And it helps to count the ways.
• • •
Let’s go back to the beginning, then. Let’s go back to the first learning laboratory of them all, to its sole occupant, and his most important contribution—the Forgetting Curve. The Forgetting Curve is exactly what it sounds like, a graph of memory loss over time. In particular, it charts the rate at which newly learned information fades from memory. It’s a learning curve, turned upside-down:
This curve, first published in the late 1880s, falls well short of breathtaking. It’s what anyone might draw if asked to guess how memory changes with time. Yet its creator, Hermann Ebbinghaus, wasn’t one for idle guesswork. He was exacting by nature, compulsive about evidence. He had to be, given his ambitions. In the late 1870s, as a young philosophy Ph.D., he zigzagged through Europe, thinking big. He longed to bridge philosophy and science, to apply rigorous measurement to some aspect of human nature or psychology. The only problem was, he didn’t know where to start. He was poking around in a secondhand Paris bookstall one afternoon when he pulled from the shelf a volume called Elements of Psychophysics by Gustav Fechner. A scientist with a mystical bent, Fechner saw a unifying mathematical connection between the inner, mental world and the outer, natural one. He argued that every human experience, even one as ephemeral as memory, should be reducible to measurable units that could be plugged into an equation of some sort. Fechner’s reputation as a scientist—he’d done elegant experiments on the sensation of touch—lent his more grandiose ideas some weight.
As he read, Ebbinghaus felt something inside him shift—a sensation he would describe, years later, to a student. He must have glimpsed his future as well, right then and there, because he later dedicated his greatest work, Memory: A Contribution to Experimental Psychology, to Fechner.
The memory equation. Did it even exist? If so, could it be written down?
Memories come in so many shapes and sizes. There are the hour-long and the lifelong; there are dates and numbers, recipes and recitals; not to mention stories, emotional perceptions, the look on a child’s face when he’s dropped at the bus stop on the first day of school, the knowing smile shared between two friends who think no one is looking: the tapestry of hijinks and heartbreaks that make up a life. Our ability to recall specific facts also varies widely. Some people are good with names and faces; others are much better at retrieving numbers, dates, formulas. How on earth do you measure such a shape-shifting ghost, much less study it?
A generation of scientists before Ebbinghaus had essentially stood down, taking a pass on the question. It was too much. The variables were overwhelming.
Yet where some saw a justified caution, Ebbinghaus saw a lack of nerve. “At the very worst we should prefer to see resignation arise from the failure of earnest investigations rather than from the persistent, helpless astonishment in the face of the difficulties,” he wrote, in explaining his motives for pursuing the memory equation. He would take the dare if there was no one else. He reasoned from first principles. To study how the brain stores new information, he needed information that was, in fact, new. A list of nouns or names or numbers simply wouldn’t do; people walk around with an enormous storehouse of associations for all of these things. Even abstract sketches have a Rorschach-like, evocative quality. Stare long enough at a cloud and it begins to look like a dog’s head, which in turn activates hundreds of dog-related circuits in the brain. Our brain can impute meaning to almost anything.
How Ebbinghaus arrived at his solution remains a mystery. “Was it an invention in the commonly accepted sense of the term, that is to say, deliberate?” wrote the American psychologist David Shakow, much later, in a biographical essay. “Or was it largely a discovery? What part did the gurgle of an infant, a transient progression to infancy, the reading of Jabberwocky, the expletives of the Paris coachman for the London cabbie, play?”
What Ebbinghaus created was a catalog of nonsense sounds. These were single syllables, formed by sticking a vowel between two consonants. RUR, HAL, MEK, BES, SOK, DUS. By and large, they were meaningless.
Ebbinghaus had found his generic memory “units.”
He created about 2,300 of them—a pool of all possible syllables, or at least as many as he could think of. He put together lists of the syllables, random groupings of between seven and thirty-six each. Then he began to memorize one list at a time, reading the syllables out loud, pacing himself with a metronome, keeping track of how many repetitions he needed to produce a perfect score.
By the time he landed a job as an instructor, at the University of Berlin in 1880, he’d logged more than eight hundred hours of practice with his nonsense sounds. He continued the work in his small office, pacing the floor, a compact, bushy-bearded man in Ben Franklin spectacles, spitting out the syllables at a rate of as many as 150 a minute. (In another era or another country, he might have been hauled off and fitted with a lunatic suit.) He tested himself at various intervals: Twenty minutes after studying. An hour. A day later, then a week. He varied the duration of his practice sessions, too, and found (surprise) that more practice sessions generally resulted in higher test scores and a slower rate of forgetting.
In 1885, he published his results in Memory: A Contribution to Experimental Psychology, describing a simple way to calculate the rate of forgetting after a study session. The equation wasn’t much to look at, but it was the first rigorous principle in the emerging branch of psychology—and precisely what he’d set out to find a decade earlier in that Paris bookstall.
Ebbinghaus had his equation (others would plot it as a graph).
He hadn’t changed the world. He did, however, launch the science of learning. “It is not too much to say that the recourse to nonsense syllables, as a means to the study of association, marks the most considerable advance in this chapter of psychology since the time of Aristotle,” wrote English scientist Edward Titchener a generation later.
Ebbinghaus’s Forgetting Curve captured the minds of many theorists and would not let go. In 1914, the influential American education researcher Edward Thorndike turned Ebbinghaus’s curve into a “law” of learning. He called it the Law of Disuse, which asserted that learned information, without continued use, decays from memory entirely—i.e., use it or lose it.
The law felt right. It certainly seemed to square with experience, defining how most people thought of learning and to this day still do. Yet that definition hides more than it reveals.
• • •
Here’s an at-home exercise that is simple, painless, and full of literary nutrition. Take five minutes and study the verse below. Read it carefully and try to commit it to memory. It’s from the poet Henry Wadsworth Longfellow’s “The Wreck of the Hesperus.”
At daybreak, on the bleak sea-beach,
A fisherman stood aghast,
To see the form of a maiden fair,
Lashed close to a drifting mast.
The salt sea was frozen on her breast,
The salt tears in her eyes;
And he saw her hair, like the brown sea-weed,
On the billows fall and rise.
Such was the wreck of the Hesperus,
In the midnight and the snow!
Christ save us all from a death like this,
On the reef of Norman’s Woe!
Okay, now put the book aside and make a cup of coffee, take a walk, listen to the news. Distract yourself for about five minutes, the same amount of time you took to study it. Then, sit and write down as much of the poem as you can. Save the result (you’ll need it later).
This is exactly the test that an English teacher and researcher named Philip Boswood Ballard began administering to schoolchildren in the early 1900s in London’s working-class East End. The children were thought to be poor learners, and Ballard was curious to find out why. Was it a deficit of initial learning? Or did something happen later that interfered with recall? To find out, he had them study various material, including ballads like Longfellow’s, to see if he could pinpoint the source of their learning problems.
Only the children had no obvious learning deficits that Ballard could find. On the contrary.
Their scores five minutes after studying were nothing special. Some did well and others didn’t. Ballard wasn’t finished, however. He wanted to know what happened to the studied verse over time. Did memory somehow falter in the days after these children studied? To find out, he gave them another test, two days later. The students were not expecting to be retested and yet their scores improved by an average of 10 percent. Ballard tested them once more, again unannounced, days later.
“J.T. improved from 15 to 21 lines in three days,” he wrote of one student. “Imagined she saw the lines in front of her.” Of another, who improved from three to eleven lines in seven days, he remarked: “Pictured the words on the blackboard (the poetry in this case was learnt from the blackboard).” A third, who recalled nine lines on the first test and, days later, thirteen, told Ballard, “as I began to write it, I could picture it on the paper before me.”
This improvement wasn’t merely odd. It was a flat contradiction of Ebbinghaus.
Ballard doubted what he was seeing and ran hundreds of additional tests, with more than ten thousand subjects, over the next several years. The results were the same: Memory improved in the first few days without any further study, and only began to taper off after day four or so, on average.
Ballard reported his findings in 1913, in a paper that seems to have caused mostly confusion. Few scientists appreciated what he’d done, and even today he is little more than a footnote in psychology, a far more obscure figure than Ebbinghaus. Still, Ballard knew what he had. “We not only tend to forget what we have once remembered,” he wrote, “but we also tend to remember what we have once forgotten.”
Memory does not have just one tendency over time, toward decay. It has two.
The other—“reminiscence,” Ballard called it—is a kind of growth, a bubbling up of facts or words that we don’t recall having learned in the first place. Both tendencies occur in the days after we’ve tried to memorize a poem or a list of words.
What could possibly be going on?
One clue comes from Ebbinghaus. He had tested memory using only nonsense syllables. The brain has no place to “put” these letter trios. They’re not related to one another or to anything else; they’re not part of a structured language or pattern. The brain doesn’t hold on to nonsense syllables for long, then, because they are nonsense. Ebbinghaus acknowledged as much himself, writing that his famous curve might not apply to anything more than what he had studied directly.
Forgetting, remember, is not only a passive process of decay but also an active one, of filtering. It works to block distracting information, to clear away useless clutter. Nonsense syllables are clutter; Longfellow’s “The Wreck of the Hesperus” is not. The poem may or may not become useful in our daily life, but at least it is nested in a mesh of neural networks representing words and patterns we recognize. That could account for why there would be a difference in how well we remember nonsense syllables versus a poem, a short story, or other material that makes sense. Yet it does not explain the increase in clarity after two days without rehearsal, the “salt tears” and “hair like brown sea-weed” floating up from the neural deep. Those “slow” East Enders showed Ballard that remembering and forgetting are not related to each other in the way everyone assumed.
The Forgetting Curve was misleading and, at best, incomplete. It might even need to be replaced altogether.
• • •
In the decades after Ballard published his findings, there was a modest flare of interest in “spontaneous improvement.” The effect should be easy to find, scientists reasoned, in all kinds of learning. Yet it wasn’t. Researchers ran scores of experiments, and the results were all over the place. In one huge 1924 trial, for instance, people studied a word list, and took a test immediately afterward. They were then given a follow-up test, after varying delays: eight minutes, sixteen minutes, three days, a week. They did worse over time, on average, not better.
In a 1937 experiment, subjects who studied nonsense syllables showed some spontaneous improvement after an initial exam—but only for about five minutes, after which their scores plunged. A widely cited 1940 study found that people’s recall of a set of words, a set of brief sentences, and a paragraph of prose all declined over a twenty-four-hour period. Even when researchers found improvement for one kind of material, like poetry, they’d find the opposite result for something else, like vocabulary lists. “Experimental psychologists began to tinker with Ballard’s approach and, as if struggling in quicksand, became progressively mired in confusion and doubt,” wrote Matthew Hugh Erdelyi, of Brooklyn College, in his history of the era, The Recovery of Unconscious Memories.
The mixed findings inevitably led to questions about Ballard’s methods. Were the children he tested really recalling more over time, or was their improvement due to some flaw in the experimental design? It wasn’t a rhetorical question. What if, for example, the children had rehearsed the poem on their own time, between tests? In that case, Ballard had nothing.
In an influential review of all published research up through 1943, one British learning theorist, C. E. Buxton, concluded that Ballard’s spontaneous improvement effect was a “now-you-see-it-now-you-don’t phenomenon”—in other words, a phantom. It wasn’t long before many scientists followed Buxton’s lead and begged off the hunt. There were far better things to do with the tools of psychology than chase phantoms, and certainly more culturally fashionable ones.
Freudian therapy was on the rise, and its ideas of recovered memories easily trumped Ballard’s scraps of Longfellow for sex appeal. The two men’s conceptions of recovery were virtually identical, except that Freud was talking about repressed emotional trauma. Excavating those memories and “working through” them could relieve chronic, disabling anxiety, he claimed. It could change lives. If those were phantoms, they were far more lifelike than a heap of recited poetry.
Besides, the real juice in learning science by the middle of the century was in reinforcement. It was the high summer of behaviorism. The American psychologist B. F. Skinner showed how rewards and punishments could alter behavior, and accelerate learning in many circumstances. Skinner tested various reward schedules against one another and got striking results: An automatic reward for a correct answer leads to little learning; occasional, periodic rewards are much more effective. Skinner’s work, which was enormously influential among educators, focused on improving teaching, rather than on the peculiarities of memory.
Yet Ballard’s findings didn’t disappear completely. They continued to marinate in the minds of a small group of psychologists who couldn’t shake the idea that something consequential might be slipping through the cracks. In the 1960s and 1970s, these curious few began to separate the poetry from the nonsense.
The Ballard effect was, and is, real. It was not due to an experimental design flaw; the children in his studies could not have rehearsed lines that they did not remember after the first test. You can’t practice what you don’t remember. The reason researchers had had so much trouble isolating Ballard’s “reminiscence” was because the strength of this effect is highly dependent on the material being used. For nonsense syllables, and for most lists of vocabulary words or random sentences, it’s zero: There’s no spontaneous improvement on test scores after a day or two. By contrast, reminiscence is strong for imagery, for photographs, drawings, paintings—and poetry, with its word-pictures. And it takes time to happen. Ballard had identified the “bubbling up” of new verse in the first few days after study, when it’s strongest. Other researchers had looked for it too early, minutes afterward, or too late, after a week or more.
Matthew Erdelyi was one of those who was instrumental in clarifying reminiscence, and he began by testing a junior colleague, Jeff Kleinbard, then at Stanford University. Erdelyi gave Kleinbard a group of forty pictures to study in a single sitting, on the pretext that he “should have the experience of being a subject” before conducting experiments of his own. In fact, he was a subject, and Erdelyi tested him repeatedly, without warning, over the following week. The results were so clear and reliable—Kleinbard remembered increasingly more on tests over the first two days—that the two of them set up larger studies. In one, they had a group of young adults try to memorize a series of sixty sketches. The participants saw the sketches one at a time, projected on a screen, five seconds apart: simple drawings of things like a boot, a chair, a television.
The group took a test right after and tried to recall all sixty, in seven minutes, writing down a word to describe each sketch recalled (the sketches had no accompanying words). The average score was 27. Ten hours later, however, their average was 32; a day later, 34; by four days, it was up to 38, where it plateaued. A comparison group, who studied sixty words presented on slides, improved from 27 to 30 in the first ten hours—and no more. Their scores slipped slightly over the next several days. Soon it was beyond dispute that memory, as Erdelyi put it in a recent paper, “is a heterogeneous, mottled system that both improves and declines over time.”
Which left theorists with a larger riddle. Why does recall of pictures improve while recall of word lists does not?
Scientists had speculated about the answers all along. Maybe it was a matter of having more time to search memory (two tests versus one). Or perhaps the delay between tests relaxed the mind, eased fatigue. Yet it wasn’t until the 1980s that psychologists had enough hard evidence to begin building a more complete model that accounts for the Ballard effect and other peculiarities of memory. The theory that emerged is less a grand blueprint for how the mind works than a set of principles based on research, a theory that encompasses Ebbinghaus and Ballard, as well as many other seemingly opposed ideas and characters. The scientists who have shepherded the theory along and characterized it most clearly are Robert Bjork of UCLA and his wife, Elizabeth Ligon Bjork, also at UCLA. The new theory of disuse (“Forget to Learn,” as we’re calling it) is largely their baby.
The first principle theory is this: 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. The multiplication table is a good example. It’s drilled into our heads in grade school, and we use it continually throughout life, in a wide variety of situations, from balancing the bank account to calculating tips to helping our fourth grader with homework. Its storage strength is enormous.
According to the Bjorks’ theory, storage strength can increase but it never decreases.
This does not mean that everything we see, hear, or say is stored forever, until we die. More than 99 percent of experience is fleeting, here and gone. The brain holds on to only what’s relevant, useful, or interesting—or may be so in the future. It does mean that everything we have deliberately committed to memory—the multiplication table, a childhood phone number, the combination to our first locker—is all there, and for good. This seems beyond belief at first, given the sheer volume of information we absorb and how mundane so much of it is. Remember from chapter 1, though, that biologically speaking there’s space to burn: in digital terms, storage space for three million TV shows. That is more than enough to record every second of a long life, cradle to grave. Volume is not an issue.
As for the mundane, it’s impossible to prove that it’s all there, every meaningless detail. Still, every once in a while the brain sends up a whisper of dumbfounding trivia. It happens to everyone throughout life; I’ll offer an example of my own. In researching this book, I spent some time in college libraries, the old-school kind, with basements and subbasements full of stacks of old books that create the vague sensation of being on an archaeological dig. It was the musty smell, I think, that on one afternoon took me back to a month-long period in 1982 when I worked at my college library. I was hunting down an old book in some deserted corner of the Columbia University library, feeling claustrophobic and lost—when a name popped into my head. Larry C______. The name of the man at the library who was (I guess) my supervisor. I met him once. Lovely guy—only I had no idea I ever knew his name. Still, here I was, seeing him in my mind’s eye walking away from that one meeting, and even seeing that his boat shoes were worn in the back the way some people’s get, angling toward one another.
One meeting. The shoes. Perfectly meaningless. Yet I must have known the name, and I must have stored that impression of him walking off. Why on earth would I have kept that information? Because it was, at one point in my life, useful. And the Forget to Learn theory says: If I stored it, it’s in there for good.
That is, no memory is ever “lost” in the sense that it’s faded away, that it’s gone. Rather, it is not currently accessible. Its retrieval strength is low, or near zero.
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, and its capacity is relatively small (compared to storage). At any given time, we can pull up only a limited number of items in connection with any given cue or reminder.
For example, a quack-quack cell phone ring overheard on the bus might bring to mind the name of a friend who has the same ring, as well as several people who are owed calls. It may also trigger an older vision of the family dog belly-flopping into a lake to pursue a flotilla of ducks; or your first raincoat, bright yellow with a duckbill on the hood. Thousands of other quack associations, some meaningful at the time they formed, are entirely off the radar.
Compared to storage, retrieval strength is fickle. It can build quickly but also weaken quickly.
One way to think of storage and retrieval is to picture a huge party in which everyone you ever met is in attendance (at the age when you last saw them). Mom and Dad; your first grade teacher; the brand-new neighbors next door; the guy who taught driver’s-ed in sophomore year: They’re all here, mingling. Retrieval is a matter of how quickly a person’s name comes to mind. Storage, by contrast, is a matter of how familiar the person is. Mom and Dad, there’s no escaping them (retrieval high, storage high). The first grade teacher, her name isn’t jumping to mind (retrieval low) but that’s definitely her right there over by the door (storage high). The new neighbors, by contrast, just introduced themselves (“Justin and Maria”—retrieval high), but they’re not familiar yet (storage low). Tomorrow morning, their names will be harder to recall. As for the driver’s-ed guy, the name’s not coming back, and he wouldn’t be so easy to pick out of a lineup, either. The class was only two months long (retrieval low, storage low).
The act of finding and naming each person increases both strengths, remember. The first grade teacher—once she’s reintroduced—is now highly retrievable. This is due to the passive side of forgetting, the fading of retrieval strength over time. The theory says that that drop facilitates deeper learning once the fact or memory is found again. Again, think of this aspect of the Forget to Learn theory in terms of building muscle. Doing pull-ups induces tissue breakdown in muscles that, after a day’s rest, leads to more strength the next time you do the exercise.
That’s not all. The harder we have to work to retrieve a memory, the greater the subsequent spike in retrieval and storage strength (learning). The Bjorks call this principle desirable difficulty, and its importance will become apparent in the coming pages. That driver’s-ed teacher, once he’s spotted, is now way more familiar than he was before, and you may remember things about him you forgot you knew: not just his name and nickname but his crooked smile, his favorite phrases.
The brain developed this system for a good reason, the Bjorks argue. 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.
This combination of flighty retrieval and steady storage—the tortoise and the hare—is no less important to modern-day survival. Kids who grow up in North American households, for example, learn to look people in the eye when speaking, especially a teacher or parent. Kids in Japanese homes learn the opposite: Keep your gaze down, especially when speaking to an authority figure. To move successfully from one culture to the other, people must block—or forget—their native customs to quickly absorb and practice the new ones. The native ways are hardly forgotten; their storage strength is high. But blocking them to transition to a new culture drives down their retrieval strength.
And being able to do this can be a matter of life or death. An Australian who moves to the United States, for instance, must learn to drive on the right side of the road instead of the left, upending almost every driving instinct he has. There’s little room for error; one Melbourne daydream and he wakes up in a ditch. Here again, the memory system forgets all the old instincts to make room for the new ones. And that’s not all. If twenty years later he gets homesick and moves back to Australia, he will have to switch to driving on the left again. Yet that change will come much more easily than the first one did. The old instincts are still there, and their storage strength is still high. The old dog quickly relearns old tricks.
“Compared to some kind of system in which out-of-date memories were to be overwritten or erased,” Bjork writes, “having such memories become inaccessible but remain in storage has important advantages. Because those memories are inaccessible, they don’t interfere with current information and procedures. But because they remain in memory they can—at least under certain circumstances—be relearned.”
Thus, forgetting is critical to the learning of new skills and to the preservation and reacquisition of old ones.
Now let’s return to our friend Philip Ballard. The first test his students took not only measured how much of the “Hesperus” poem they remembered. It also increased the storage and retrieval strengths of the verse they did remember, making it more firmly anchored in memory and more easily accessible than it was before the test. Hit, unexpectedly, with the same test two days later, most of the lines they recalled on test number 1 came back clearly and quickly—and as a result, their brains had time to scrounge for more words, using the remembered verse as a skeleton guide, a partially completed jigsaw puzzle, a packet of cues to shake loose extra lines. This is a poem, after all, swollen with imagery and meaning, precisely the material that shows the strongest “reminiscence” effect of all.
Voilà! They do better.
Yes, the Hesperus will eventually sink if the brain stops thinking about it, and its retrieval strength will inch toward zero. But a third test, and a fourth, would anchor the poem in memory more richly still, as the brain—now being called on to use the poem regularly—would continue its search for patterns within the poem, perhaps pulling up another half line or two with each exam. Will it all come back, with enough testing, even if only half was remembered the first time? Not likely. You get something back, not everything.
Try it yourself, after a day or two. Write down as much of the “The Wreck of the Hesperus” as you can, without looking. Give yourself as much time as you took on the first test at the top of the chapter. Compare the results. If you’re like most people, you did a little better on the second test.
Using memory changes memory—and for the better. Forgetting enables and deepens learning, by filtering out distracting information and by allowing some breakdown that, after reuse, drives retrieval and storage strength higher than they were originally. Those are the basic principles that emerge from brain biology and cognitive science, and they underlie—and will help us understand—the various learning techniques yet to come.
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