in Mia’s
case, the distinctive moves that will enable her to hit the ground without breaking an ankle, or worse.3
Consolidation
The pro cess of strengthening these mental repre sen ta tions for long- term memory is called consolidation. New learning is labile: its meaning is not fully formed and therefore is easily altered. In consolidation, the brain reorganizes and stabilizes the memory traces. This may occur over several hours or longer and involves deep pro cessing of the new material, during which scientists believe that the brain replays or rehearses the learning, giving it meaning, fi lling in blank spots, and making connections to past experiences and to other knowledge already stored in long- term memory. Prior knowledge is a prerequisite for making sense of new learning, and forming those connections is an important task of consolidation. Mia’s considerable athletic skills, physical self- awareness, and prior experience represent a large body of knowledge to which the elements of a successful PLF would fi nd many connections. As we’ve noted, sleep seems to help memory consolidation, but in any case, consolidation and transition of learning to long-term storage occurs over a period of time.
An apt analogy for how the brain consolidates new learning may be the experience of composing an essay. The fi rst draft is rangy, imprecise. You discover what you want to say by trying to write it. After a couple of revisions you have sharpened the piece and cut away some of the extraneous points.
You put it aside to let it ferment. When you pick it up again
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a day or two later, what you want to say has become clearer in your mind. Perhaps you now perceive that there are three main points you are making. You connect them to examples and supporting information familiar to your audience. You rearrange and draw together the elements of your argument to make it more effective and elegant.
Similarly, the pro cess of learning something often starts out feeling disor ga nized and unwieldy; the most important aspects are not always salient. Consolidation helps or ga nize and solid-ify learning, and, notably, so does retrieval after a lapse of some time, because the act of retrieving a memory from long- term storage can both strengthen the memory traces and at the same time make them modifi able again, enabling them, for example, to connect to more recent learning. This pro cess is called re consolidation. This is how retrieval practice modifi es and strengthens learning.
Suppose that on day 2 of jump school, you’re put on the spot to execute your parachute landing fall and you struggle to recall the correct posture and compose yourself— feet and knees together, knees slightly bent, eyes on the horizon— but in the refl ex to break your fall you throw your arm out, forgetting to pull your elbows tight to your sides. You could have broken the arm or dislocated your shoulder if this were the real deal. This effort to reconstruct what you learned the day before is ragged, but in making it, critical elements of the maneuver come clearer and are reconsolidated for stronger memory. If you’re practicing something over and over in rapid- fi re fashion, whether it’s your parachute landing fall or the conju-gation of foreign verbs, you’re leaning on short- term memory, and very little mental effort is required. You show gratifying improvement rather quickly, but you haven’t done much to strengthen the underlying repre sen ta tion of those skills. Your per for mance in the moment is not an indication of durable
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learning. On the other hand, when you let the memory recede a little, for example by spacing or interleaving the practice, retrieval is harder, your per for mance is less accomplished, and you feel let down, but your learning is deeper and you will retrieve it more easily in the future.4
Retrieval
Learning, remembering, and forgetting work together in interesting ways. Durable, robust learning requires that we do two things. First, as we recode and consolidate new material from short- term memory into long- term memory, we must anchor it there securely. Second, we must associate the material with a diverse set of cues that will make us adept at recalling the knowledge later. Having effective retrieval cues is an aspect of learning that often goes overlooked. The task is more than committing knowledge to memory. Being able to retrieve it when we need it is just as important.
The reason we don’t remember how to tie knots even after we’ve been taught is because we don’t practice and apply what we’ve learned. Say you’re in the city park one day and come across an Ea gle Scout teaching knots. On a whim you take an hour’s lesson. He demonstrates eight or ten specimens, explains what each is useful for, has you practice tying them, and sends you away with a short length of rope and a cheat sheet. You head home committed to learning these knots, but life is full, and you fail to practice them. They are soon forgotten, and this story could end there, with no learning. But then, as it happens, the following spring you buy a small fi shing boat, and you want to attach an anchor on a line. With rope in hand and feeling mildly stumped, you recall from your lesson that there was a knot for putting a loop in the end of a line. You are now practicing retrieval. You fi nd your cheat
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sheet and relearn how to tie a bowline. You put a small loop in the rope and then take the short end and draw it through, silently reciting the little memory device you were given: the rabbit comes up from his hole, goes around the tree, and goes back down. Retrieval again. A little snugging- up, and there you have your knot, a dandy piece of scoutcraft of the kind you’d always fancied knowing. Later, you put a piece of rope beside the chair where you watch TV and practice the bowline during commercials. You are doing spaced practice. Over the coming weeks you’re surprised at how many little jobs are easier if you have a piece of rope with a loop in the end. More spaced practice. By August you have discovered every possible use and purpose in your life for the bowline knot.
Knowledge, skills, and experiences that are vivid and hold signifi cance, and those that are periodically practiced, stay with us. If you know you’re soon to throw yourself out of a troop transport, you listen up good when they’re telling you when and how to pull the rip cord on your reserve chute, or what can go wrong at twelve hundred feet and how to “just sort of swim out of it.” The mental rehearsal you conduct while lying in your bunk too tired to sleep and wishing the next day was already over and well- jumped is a form of spaced practice, and that helps you, too.
Extending Learning: Updating Retrieval Cues There’s virtually no limit to how much learning we can remember as long as we relate it to what we already know. In fact, because new learning depends on prior learning, the more we learn, the more possible connections we create for further learning. Our retrieval capacity, though, is severely limited.
Most of what we’ve learned is not accessible to us at any given moment. This limitation on retrieval is helpful to us: if every
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memory were always readily to hand, you would have a hard time sorting through the sheer volume of material to put your fi nger on the knowledge you need at the moment: where did I put my hat, how do I sync my electronic devices, what goes into a perfect brandy Manhattan?
Knowledge is more durable if it’s deeply entrenched, meaning that you have fi rmly and thoroughly comprehended a concept, it has practical importance or keen emotional weight in your life, and it is connected with other knowledge that you hold in memory. How readily you can recall knowledge from your internal archives is determined by context, by recent use, and by the number and vividness of cues that you have linked to the knowledge and can call on to help bring it forth.5
Here’s the tricky part. As you go through life, you often need to forget cues associated with older, competing memories so as to associate them successfully with new ones. To learn Italian in middle age, you may have to forget your high school French, because every time you think “to be” and hope to come up with the Italian essere, up pops etre, despite your most earnest intentions. Traveling in En gland, you have to suppress your cues to drive on the right side of the road so you can establish reliable cues to stay on the left. Knowledge that is well entrenched, like real fl uency in French or years of experience driving on the right side of the road, is easily relearned later, after a period of disuse or after being interrupted by competition for retrieval cues. It’s not the knowledge itself that has been forgotten, but the cues that enable you to fi nd and retrieve it. The cues for the new learning, driving on the left, displace those for the old, driving on the right (if we are lucky).
The paradox is that some forgetting is often essential for new learning.6 When you change from a PC to a Mac, or from one Windows platform to another, you have to do enormous
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forgetting in order to learn the architecture of the new system and become adept at manipulating it so readily that your attention can focus on doing your work and not on working the machine. Jump school training provides another example: After their military ser vice, many paratroopers take an interest in smoke jumping. Smokejumpers use different airplanes, different equipment, and different jump protocols. Having trained at the army’s jump school is cited as a distinct disadvantage for smoke jumping, because you have to unlearn one set of procedures that you have practiced to the point of re-fl ex and replace them with another. Even in cases where both bodies of learning seem so similar to the uninitiated— jumping out of an airplane with a parachute on your back— you may have to forget the cues to a complex body of learning that you possess if you are to acquire a new one.
We know this problem of reassigning cues to memory from our own lives, even on the simplest levels. When our friend Jack fi rst takes up with Joan, we sometimes call the couple
“Jack and Jill,” as the cue “Jack and” pulls up the old nursery rhyme that’s so thoroughly embedded in memory. About the time we have “Jack and” reliably cuing “Joan,” alas, Joan throws him over, and he takes up with Jenny. Good grief!
Half of the time that we mean to say Jack and Jenny we catch ourselves saying Jack and Joan. It would have been easier had Jack picked up with Katie, so that the trailing K sound in his name handed us off to the initiating K in hers, but no such luck. Alliteration can be a handy cue, or a subversive one. In all of this turmoil you don’t forget Jill, Joan, or Jenny, but you
“repurpose” your cues so that you can keep pace with the changing opera of Jack’s life.7
It is a critical point that as you learn new things, you don’t lose from long- term memory most of what you have learned well in life; rather, through disuse or the reassignment of cues,
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you forget it in the sense that you’re unable to call it up easily.
For example, if you’ve moved several times, you may not be able to recall a previous address from twenty years ago. But if you are given a multiple choice test for the address, you can probably pick it out easily, for it still abides, as it were, in the uncleaned closet of your mind. If you have ever immersed yourself in writing stories of your past, picturing the people and places of earlier days, you may have been surprised by the memories that started fl ooding back, things long forgotten now coming to mind. Context can unleash memories, as when the right key works to open an old lock. In Marcel Proust’s Remembrance of Things Past, the narrator grieves over his inability to recall the days of his adolescence in the French village of his aunt and uncle, until one day the taste of a cake dipped in lime blossom tea brings it all rushing back, all the people and events he thought had long since been lost to time.
Most people have experiences like Proust’s when a sight or sound or smell brings back a memory in full force, even some episode you have not thought about in years.8
Easier Isn’t Better
Psychologists have uncovered a curious inverse relationship between the ease of retrieval practice and the power of that practice to entrench learning: the easier knowledge or a skill is for you to retrieve, the less your retrieval practice will benefi t your retention of it. Conversely, the more effort you have to expend to retrieve knowledge or skill, the more the practice of retrieval will entrench it.
Not long ago the California Polytechnic State University baseball team, in San Luis Obispo, became involved in an interesting experiment in improving their batting skills. They were all highly experienced players, adept at making solid contact
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