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.
Part Two
Retention
Chapter Three
Breaking Good Habits
The Effect of Context on Learning
Don’t forget your brain vitamins.
In college, that’s what passed for exam-taking advice, at least among those of us who frequented a hippified pill shop in downtown Boulder. There, on a shelf behind the counter, between vials of brown serum, lotus seeds, and hemp balm, were bottles of something called “Study Aid.” The label on the back listed herbs, root products, fiber, and “natural extracts.”
The not-so-secret ingredient was, most likely, speed.
One dose delivered a bump in confidence and motivation, along with a night of focused study time. That was the upside. The downside, after sequential doses, was a ragged withdrawal that dead-ended into a sudden, dreamless sleep—not ideal for operating heavy machinery, and a clear and present danger when sitting through a long exam. Close your eyes for a second and you were out, pencil clattering to the floor, liable to awake to the words, “Time’s up, please hand in your work.”
The don’t-forget-your-vitamins advice meant, above all, stay conscious. When in doubt, take an extra dose to cross the finish line. Over time, though, I began to wonder if there was something more to it. When I studied on a vitamin, I worked with a kind of silly abandon, talking to myself, pacing. And when it came time to take the test, I wanted some of that manic energy back. I wanted to hear the internal conversation, to have the same physical connection with the material. I began to think—we all did—that taking “Study Aid” right before the test made that connection happen. It wasn’t only keeping us upright; it made us feel mentally closer to what we’d studied, and as a result we thought we remembered more of it.
Did we actually know this to be true? No, of course not, we never tested it—we wouldn’t have known how if we’d wanted to. Yet we felt like we had a lucky charm, a way to put our head “in the same place” during test-taking as during studying. Essential it was, too, especially during finals week, with two and sometimes three tests falling on the same day. That kind of pressure drives people deep into their worst habits, whether chocolate and cigarettes, brain vitamins and nail-biting, cases of diet cola, or much stronger stuff. When hunkered down in this psychological survival mode, it can be a profound comfort to believe that a favorite “study aid” also improves exam performance. And so we did.
“Brain chemistry,” our theory went, “you want the same brain chemistry.”
For a long time afterward, I looked back on that kind of theorizing as pure rationalization, the undergraduate mind at its self-justifying finest. We had so many crackpot theories then, about dating and getting rich and studying, that I’d discarded the whole list. Still, millions of students have developed some version of the brain chemistry idea, and I think its enduring attraction is rooted in something deeper than wishful thinking. The theory fits in nicely with what we’ve been told about good study habits from Day 1—be consistent.
Consistency has been a hallmark of education manuals since the 1900s, and the principle is built into our every assumption about good study habits. Develop a ritual, a daily schedule, a single place and time set aside for study and nothing else. Find a private corner of the house or the library, and a quiet niche of the day, early or late. These ideas go back at least to the Puritans and their ideal of study as devotion, but they have not changed a whit. “Choose an area that is quiet and free from distractions,” begins a study guide from Baylor University, though it could be from any institution. It continues:
“Develop a study ritual to use each time you study.”
“Use earplugs or a headset to block out noise.”
“Say no to those who want to alter your study time.”
Et cetera. It is all about consistency.
And so is the “Study Aid” brain chemistry theory, if you think about it. Using the same “vitamin”—or, okay, mind-altering substance—to prepare and, later, to perform may not be particularly Puritan. But it’s nothing if not consistent.
It is also, within reason, correct.
Studying while seriously impaired is wasted time, in more ways than one, as millions of students have learned the hard way. Yet, generally speaking, we perform better on tests when in the same state of mind as when we studied—and, yes, that includes mild states of intoxication from alcohol or pot, as well as arousal from stimulants. Moods, preoccupations, and perceptions matter, too: how we feel while studying, where we are, what we see and hear. The scientific investigation into these influences—the inner mental context, so to speak, as well as the outer one—has revealed subtle dimensions of learning that we rarely, if ever, notice but can exploit to optimize our time. Along the way, paradoxically, this research has also demolished the consistency doctrine.
• • •
The story begins twenty feet underwater, just off the coast of Oban, Scotland.
Oban, on the Sound of Mull and facing the islands known as the Southern Hebrides, is a premier diving destination. It’s within easy range of the Rondo, an American steamer that sank here in 1934 and sits—jackknifed, nose-down—in 150 feet of water,
a magnet for explorers in scuba gear. A half dozen other shipwrecks are also close—the Irish Thesis, lost in 1889; the Swedish Hispania, which went down in 1954—and the waters course with dogfish, octopus, cuttlefish, and the psychedelic sea slugs called nudibranchs.
It was here, in 1975, that a pair of psychologists from nearby Stirling University recruited a group of divers to participate in an unusual learning experiment.
The psychologists, D. R. Godden and A. D. Baddeley, wanted to test a hypothesis that many learning theorists favored: that people remember more of what they studied when they return to that same study environment. This is a variation on the detective novel line, “Now, Mrs. Higgins, let’s return to the night of the murder. Tell me exactly what you saw and heard.” Like the detective, psychologists hypothesized that features of the study location—the lighting, the wallpaper, the background music—provide the brain “cues” to shake free more information. The difference is that Mrs. Higgins is trying to revisit a dramatic scene, an autobiographical memory, and the researchers were applying the same idea—reinstatement, they called it—to facts, to what the Estonian psychologist Endel Tulving called “semantic memories.”
The idea seems far-fetched. Who on earth remembers what was playing through the headphones when he or she learned the definition of an isosceles triangle, or an ionic bond, or the role of Viola in Twelfth Night? And when Godden and Baddeley dreamed up their experiment, the evidence for reinstatement was shabby at best. In one previous experiment, for example, participants tried to memorize word lists they heard through earphones while standing with their heads inside a box containing multicolored flashing lights (two dropped out due to nausea). In another, subjects studied nonsense syllables while strapped to a board, which tipped on an axis like a teeter-totter, as in some cruel school yard prank.
How We Learn Page 5