with the ball, but they agreed to take extra batting practice twice a week, following two different practice regimens, to see which type of practice produced better results.
Hitting a baseball is one of the hardest skills in sports. It takes less than half a second for a ball to reach home plate. In this instant, the batter must execute a complex combination of perceptual, cognitive, and motor skills: determining the type of pitch, anticipating how the ball will move, and aiming and timing the swing to arrive at the same place and moment as the ball. This chain of perceptions and responses must be so deeply entrenched as to become automatic, because the ball is in the catcher’s mitt long before you can even begin to think your way through how to connect with it.
Part of the Cal Poly team practiced in the standard way.
They practiced hitting forty- fi ve pitches, evenly divided into three sets. Each set consisted of one type of pitch thrown fi fteen times. For example, the fi rst set would be fi fteen fastballs, the second set fi fteen curveballs, and the third set fi fteen changeups. This was a form of massed practice. For each set of 15 pitches, as the batter saw more of that type, he got gratifyingly better at anticipating the balls, timing his swings, and connecting. Learning seemed easy.
The rest of the team were given a more diffi cult practice regimen: the three types of pitches were randomly interspersed across the block of forty- fi ve throws. For each pitch, the batter had no idea which type to expect. At the end of the forty-fi ve swings, he was still struggling somewhat to connect with the ball. These players didn’t seem to be developing the profi -
ciency their teammates were showing. The interleaving and spacing of different pitches made learning more arduous and feel slower.
The extra practice sessions continued twice weekly for six weeks. At the end, when the players’ hitting was assessed, the
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two groups had clearly benefi ted differently from the extra practice, and not in the way the players expected. Those who had practiced on the randomly interspersed pitches now displayed markedly better hitting relative to those who had practiced on one type of pitch thrown over and over. These results are all the more interesting when you consider that these players were already skilled hitters prior to the extra training. Bringing their per for mance to an even higher level is good evidence of a training regimen’s effectiveness.
Here again we see the two familiar lessons. First, that some diffi culties that require more effort and slow down apparent gains— like spacing, interleaving, and mixing up practice—
will feel less productive at the time but will more than compensate for that by making the learning stronger, precise, and enduring. Second, that our judgments of what learning strategies work best for us are often mistaken, colored by illusions of mastery.
When the baseball players at Cal Poly practiced curveball after curveball over fi fteen pitches, it became easier for them to remember the perceptions and responses they needed for that type of pitch: the look of the ball’s spin, how the ball changed direction, how fast its direction changed, and how long to wait for it to curve. Per for mance improved, but the growing ease of recalling these perceptions and responses led to little durable learning. It is one skill to hit a curveball when you know a curveball will be thrown; it is a different skill to hit a curveball when you don’t know it’s coming. Baseball players need to build the latter skill, but they often practice the former, which, being a form of massed practice, builds per for mance gains on short- term memory. It was more challenging for the Cal Poly batters to retrieve the necessary skills when practice involved random pitches. Meeting that challenge made the per for mance gains painfully slow but also long lasting.
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This paradox is at the heart of the concept of desirable diffi culties in learning: the more effort required to retrieve (or, in effect, relearn) something, the better you learn it. In other words, the more you’ve forgotten about a topic, the more effective relearning will be in shaping your permanent knowledge.9
How Effort Helps
Reconsolidating Memory
Effortful recall of learning, as happens in spaced practice, requires that you “reload” or reconstruct the components of the skill or material anew from long- term memory rather than mindlessly repeating them from short- term memory.10 During this focused, effortful recall, the learning is made pliable again: the most salient aspects of it become clearer, and the consequent reconsolidation helps to reinforce meaning, strengthen connections to prior knowledge, bolster the cues and retrieval routes for recalling it later, and weaken competing routes.
Spaced practice, which allows some forgetting to occur between sessions, strengthens both the learning and the cues and routes for fast retrieval when that learning is needed again, as when the pitcher tries to surprise the batter with a curveball after pitching several fastballs. The more effort that is required to recall a memory or to execute a skill, provided that the effort succeeds, the more the act of recalling or executing benefi ts the learning.11
Massed practice gives us the warm sensation of mastery because we’re looping information through short- term memory without having to reconstruct the learning from long-term memory. But just as with rereading as a study strategy, the fl uency gained through massed practice is transitory, and our sense of mastery is illusory. It’s the effortful pro cess of
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reconstructing the knowledge that triggers reconsolidation and deeper learning.
Creating Mental Models
With enough effortful practice, a complex set of interrelated ideas or a sequence of motor skills fuse into a meaningful whole, forming a mental model somewhat akin to a “brain app”. Learning to drive a car involves a host of simultaneous actions that require all of our powers of concentration and dexterity while we are learning them. But over time, these combinations of cognition and motor skills—
for example,
the perceptions and maneuvers required to parallel park or manipulate a stick shift— become ingrained as sets of mental models associated with driving. Mental models are forms of deeply entrenched and highly effi cient skills (seeing and un-loading on a curveball) or knowledge structures (a memorized sequence of chess moves) that, like habits, can be adapted and applied in varied circumstances. Expert per for mance is built through thousands of hours of practice in your area of expertise, in varying conditions, through which you accumulate a vast library of such mental models that enables you to correctly discern a given situation and instantaneously select and execute the correct response.
Broadening Mastery
Retrieval practice that you perform at different times and in different contexts and that interleaves different learning material has the benefi t of linking new associations to the material. This pro cess builds interconnected networks of knowledge that bolster and support mastery of your fi eld. It also multiplies the cues for retrieving the knowledge, increasing the versatility with which you can later apply it.
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Think of an experienced chef who has internalized the complex knowledge of how fl avors and textures interact; how ingredients change form under heat; the differing effects to be achieved with a saucepan versus a wok, with copper versus cast iron. Think of the fl y fi sher who can sense the presence of trout and accurately judge the likely species, make the right choice of dry fl y, nymph, or streamer, judge the wind, and know how and where to drop that fl y to make the trout rise.
Think of the kid on the BMX bike who can perform bunny-hops, tail whips, 180s, and wall taps off the features of an unfamiliar streetscape. Interleaving and variation mix up the contexts of practice and the other skills and knowledge with which the new material is associated. This makes our mental models more versatile, enabling us to apply our learning to a broader range of situations.
Fostering Conceptual Learning
How do humans learn concepts, for example the difference between dogs and cats? By randomly coming across dissimilar examples— Chihuahuas, tabby cats, Great Danes, picture book lions, calico cats, Welsh terriers. Spaced and interleaved exposure characterizes most of humans’ normal experience.
It’s a good way to learn, because this type of exposure strengthens the skills of discrimination— the pro cess of noticing particulars (a turtle comes up for air but a fi sh doesn’t)— and of induction: surmising the general rule (fi sh can breathe in water). Recall the interleaved study of birds in one case, and of paintings in another, that helped learners distinguish between bird types or the works of different paint ers while at the same time learning to identify underlying commonalities of the examples within a species or an artist’s body of work. When asked about their preferences and beliefs, the learners thought
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that the experience of studying multiple examples of one species of bird before studying examples of another species resulted in better learning. But the interleaved strategy, which was more diffi cult and felt clunky, produced superior discrimination of differences between types, without hindering the ability to learn commonalities within a type. As was true for the baseball players’ batting practice, interleaving produced diffi culty in retrieving past examples of a par tic u lar species, which further solidifi ed the learning of which birds are representative of a par tic u lar species.
The diffi culty produced by interleaving provides a second type of boost to learning. Interleaved practice of related but dissimilar geometric solids requires that you notice similarities and differences in order to select the correct formula for computing the volume. It’s thought that this heightened sensitivity to similarities and differences during interleaved practice leads to the encoding of more complex and nuanced repre sen ta tions of the study material— a better understanding of how specimens or types of problems are distinctive and why they call for a different interpretation or solution. Why a northern pike will strike a spoon or a crankbait, say, but a bass will happily powder his nose until you see fi t to throw him a grub or a popper.12
Improving Versatility
The retrieval diffi culties posed by spacing, interleaving, and variation are overcome by invoking the same mental pro-cesses that will be needed later in applying the learning in everyday settings. By mimicking the challenges of practical experience, these learning strategies conform to the admonition to “practice like you play, and you’ll play like you practice,”
improving what scientists call transfer of learning, which is
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