Cramming may help for next-day exams. But for long-term memory, spacing out study is what works.

By Sanjay Sarma and Luke Yoquinto,

At the end of even this strangest of academic semesters, final exams loom and — as always — students will cram for these tests, resulting often in short-lived success followed by enduring forgetfulness.

When surveyed, students claim to know that cramming isn’t the best approach, but many persist in it anyway. Procrastination isn’t the only reason. Studies have found that cramming can lead to better outcomes on test day than the same number of study-hours would, spread out. But in the weeks, months and years after students put their pencils down, the relative advantages of a spaced-out study strategy assert themselves. Much of what crammers forget, as they dive into the next semester, spacers tend to retain.

Cognitive scientists call the phenomenon responsible for this state of affairs the spacing effect. Today, thanks to more than a century’s worth of effort, they have assembled a remarkably detailed picture of how memory works, with the spacing effect standing front and center. It appears to be so important that introducing a bit of space into one’s study or practice schedule can improve long-term outcomes for just about anyone, at any age, trying to learn almost anything.

In 1885, the German psychologist Hermann Ebbinghaus sketched the spacing effect’s first outlines through a self-experiment that involved memorizing and forgetting mind-numbingly long lists of nonsensical syllables. The effect’s existence has since become one of the most robust findings in all of experimental psychology. Spaced study schedules improve students’ long-term retention across subjects including the sciences, math, new languages and vocabulary. It doesn’t apply to only school-age kids: It has also been documented in people as old as 76 and as young as 8 weeks. (Researchers can’t expect infants to pore over textbooks, but can compare how well they remember certain bodily tricks, such as kicking a device that moves a mobile hanging over their crib.)

Athletes, musicians — even surgeons — can also harness the spacing effect to improve their motor skills.

In one study from 2006, surgical residents learning to splice tiny blood vessels in rats were trained in either a spaced sequence — one session a week, for four weeks — or all at once, blasting through all four sessions in a single, “massed,” block. Expert evaluators awarded higher scores to the space-trained residents’ work. Meanwhile, only in the massed-practice group did some trainees tear their furry patients’ arteries so badly that they had to call off the exercise.

Findings from outside our species are even more striking. Our closest animal relatives exhibit the spacing effect as they navigate laboratory memory tasks. In one 1973 study, for instance, when researchers taught gorillas, orangutans and chimpanzees to tap certain photographs for a food reward, spaced training outperformed massed in terms of helping the apes remember which photos to touch. The space effect also is seen among some of our most distant animal relations, including honeybees, when trained to hungrily extend their feeding tube in response to various odors, their memory lasted longer after spaced training. The spacing effect even turns up in the tiny roundworm Caenorhabditis elegans
, which can be taught to flee chemicals that normally wouldn’t bother it.

C. elegans boasts only 302 neurons, compared with the human brain’s 86 billion. To researchers seeking to explain how and why the spacing effect occurs, it is telling that even this relative handful of cells can produce it. It hints that the origins of the spacing effect might be tangled up in the roots of memory itself.

In the theory of memory most widely accepted by cognitive scientists, information is preserved in patterns of selectively strengthened synapses: the microscopic junctions where neurons communicate with one another. Intriguingly, a number of the molecular mechanisms involved in fortifying and preserving synapse strength appear to require significant downtime between bouts of activity. To scientists working at such minute scales, these “recharging” periods are strong candidates for the source of the spacing effect.

But molecular and cellular neuroscientists aren’t the only ones who have their sights on spacing. So do cognitive psychologists, who are concerned less with how individual neurons work than how their collective activity in the brain supports thought.

In one prevailing explanation, having an item stored in your memory doesn’t necessarily mean you can easily retrieve it; sometimes, for instance, it remains perched on the “tip of your tongue,” just out of reach. To render memories more retrievable, it helps to practice recalling them, but there’s a catch. Retrieval practice works best when the memory in question is no longer fresh — and that requires the passage of time

Robert Bjork, distinguished research professor of cognitive psychology at UCLA, likes to use a cocktail party to explain this. Say “you really want to try to remember the names of the people you’re meeting,” he said in an interview for our book “Grasp: The Science Transforming How We Learn.” To remember a new name, people sometimes quickly “repeat it over and over to themselves. Not out loud, of course.” Unfortunately, he said, “that won’t do anything as far as creating long-term learning.” You can’t practice retrieving such a recent memory for the same reason an angler can’t reel in a trout that’s already lying at their feet — when it’s so close at hand, there’s no meaningful retrieval left to be done.

When you allow some time to elapse, however, recalling that memory becomes more difficult, as plausible, rival associations begin to creep in. (Was his name Jim, Jake or John?)

Counterintuitively, such moments of mild forgetfulness create an opportunity to reinforce the memory for the long term. Assuming you do successfully manage to recall Jim’s name, that act of retrieval can clear away those competing associations and grant long-lasting access to that memory.

“At some time later, looking across the room and retrieving what that person’s name is,” Bjork said, “can be a really powerful event in terms of your ability to recall that name later that evening or the next day.”

Whether viewed from the perspective of cellular neuroscience or cognitive psychology (or even at a level somewhere in between: brain scientists are now also in the hunt) the spacing effect continues to maintain its starring role in theories of how we remember. The effect is so pervasive that it may be best considered a feature of memory, not a bug.

Forgetfulness in the wake of a one-off event often comes in handy, Bjork said, letting us blissfully forget, for instance, “the name of an over-talkative seatmate on a flight.”

Meanwhile, the spacing effect makes it easier to hold on to information we encounter repeatedly, which might prove useful in the future — such as “the name of a book recommended by each of one’s seatmates on two different flights,” he says.

Any learner can apply techniques to break up massed learning — otherwise known as cramming — and create stronger memories.

Take golf, for example: “Just watch people on a driving range sometimes,” Bjork said. “It’s almost nothing but block practice.” Instead of using the same club over and over again, he recommended players switch clubs frequently, which forces them to do the hard, salutary work of mentally “reloading” their swing each time, while preventing them from settling into a comfortable but counterproductive groove.

In a bitter twist, however, one setting where spacing would be especially beneficial — school — is usually set up in a way that disincentivizes it. In its traditional forms at least, school tends to reward cramming. It bestows outsized rewards for performance on test day, and little for checking in on past subjects.

Given the extreme pressure now incumbent on students, teachers and parents, this may not be the best year to tinker any more with school schedules than the coronavirus pandemic is requiring.

But next year, as, with any luck, we return to the embrace of familiar educational institutions and practices, it may make sense for schools to step back and reassess which long-standing norms truly nurture learning, and which stand in its way.

If they do — putting less emphasis on high-stakes finals, perhaps, and more on multidisciplinary projects and other assignments that reference prior learning — then perhaps our semiannual rite of cramming will someday meet the same fate it currently imposes, and be forgotten.

Sanjay Sarma and Luke Yoquinto are co-authors of “Grasp: The Science Transforming How We Learn.” Sarma is the head of MIT Open Learning. Yoquinto is a research associate at the MIT AgeLab.

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