How We Learn (7 page)

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.