Illustrator: Ben Mather (@bensrightbrain)
“Repetition is the mother of learning.”
This proverb has been passed down for centuries and is a principle pillar of education, whether it be in the realm of teaching, studying, or practice. Repetition in education can take many forms, with some of the most widely used forms being blocked practice and rereading.
However, there are more powerful ways to create long-lasting neural connections. Here we review the concept of interleaving as a teaching and studying tool and encourage its use in medical education.
Blocked practice requires performing a single skill over and over with repetition being the key. The idea of blocked practice can be seen hitting a baseball off a tee. The tee holds the ball stationary in one location without any variation giving blocked practice in hitting balls.
Blocked practice is characterized by low levels of cognitive interference; it does not require the learner to encounter or incorporate new information. This translates to lower retention levels over time [1, 6].
Hitting one pitch type, in the same location, at the same speed, over and over without change may produce desired results during practice but is unlikely to translate to a game situation where the pitcher uses multiple pitches, thrown in different locations, and at different speeds. Athletes may be better prepared by mixing pitches during practice. In essence, they should practice like they play.
Stepping up to the plate with Interleaving
Reading the same text repeatedly or learning only about one specific topic at a time ill-prepares the learner for real life. Learners benefit from mixed topics just as a hitter benefits from seeing mixed pitches.
The approach of studying various topics instead of focusing on a single topic, also known as interleaving, better approximates real-life experience. Rather than learn one topic at a time in blocked practice, topics of study are learned in relation to other areas, and also learned across time . When the material is brought up again at a later date, it engages the long-term memory rather than relying on short term memorization. This technique works well when the individual topics are different yet connected or relate to a broader overall subject. Switching between different but related topics not only encourages retrieval of information studied previously, it connects the topics in one’s mind and makes a stronger imprint.
A simple example of this method is the use of flashcards. While reviewing, you can memorize all the cards of a certain topic over one period of time (blocked practice), or you can interleave other topics studied previously to reinforce that knowledge simultaneously. In stark contrast to blocked practice, interleaving incorporates aspects of random practice, is marked by higher levels of cognitive interference, and is more akin to real life application of the material.
Research on interleaving has consistently demonstrated its benefits, particularly when compared to other study techniques, such as re-reading or blocked practice of specific skills [2, 3, 10].
Interleaving heavily influences inductive learning, where a learner ascertains rules by observation. In one study, interleaving demonstrated a significant overall advantage to recognizing differences between species of birds and butterflies , whereas blocked practice stimulated the processing of similarities but limited a participant’s ability to learn low-discriminability categories among the examples. In another study, middle school students were given multiple practice sessions with assignments containing four different types of math problems, presented either in blocked or interleaved fashion .
Upon examination, mean test scores were nearly doubled for interleaved vs. blocked practice, and the benefit held true for both similar and dissimilar types of problems. This improvement in testing is likely due to the fact that during interleaved practice the students needed to choose the correct strategy to solve each problem, instead of assuming that the appropriate formula was the same as the previous problems in a blocked sequence. However, as interleaving naturally allows for spacing of learning, there is the possibility that some degree of the improvement seen in this study was due to spaced repetition of problems.
Interleaving and spaced repetition (reviewed here)  may be inseparable.
Subsequent studies attempted to control for spaced repetition when comparing interleaving with blocked practice [2, 4]. Interleaved practice inherently incorporates spaced repetition, whereas blocked practice is more massed in nature.
However, the benefits of interleaving were still evident even if the spacing was held constant.
In a study of fourth-grade children learning a new set of geometry concepts, one group completed practice problems in an interleaved order, whereas the other was blocked . Filler problems were incorporated between the blocked examples to allow for similar spacing as interleaving, whereas the interleaved group completed filler problems at the end. Performance in the practice session was impaired in the interleaved group, but upon testing one day later, test scores from that group were more than double that of the group who completed the problems through blocked practice, despite the addition of spacing . Thus, interleaving of practice problems demonstrated better test performance, even when spacing was held constant between the two groups.
Despite substantial evidence that interleaving improves retention and boosts test scores, it frequently impairs performance when studying. However, these “desirable difficulties,” as they’ve been termed, consistently lead to improved assimilation and retention of material [5, 10].
Thus, for studying to be most durable and strongly retained, slowing down learning and making it more challenging further engages the brain to thoroughly incorporate the material in question [1, 6]. The challenge of interleaved practice leads to improved comprehension and learning but research shows that students are resistant to this approach. In several experiments, participants were given the task to learn examples of birds within families, and in each set, learners were noted to overwhelmingly choose blocked learning strategies . However, as described above, blocking and rereading frequently create an unreliable sense of understanding and poorer test outcomes . Thus, the most effective learning techniques must be emphasized in teaching a multitude of subjects to best facilitate long-term retention and learning for students.
Pitching the perfect game to your residents
The evidence for interleaving in medical education is limited. Much of it has been extrapolated from other fields of study. The lack of evidence may create opportunity for future research when interleaving is applied. [11,12,13] The interleaving of topics in medical education is especially relevant as this closely replicates our actual workflow in a clinical environment.
We often see patients with varying complaints at the same time. We evaluate a patient with chest pain, another with abdominal pain and yet one more with dizziness and so on. On the other hand, we are unlikely to evaluate only chest pain patients on a given shift. Since interleaving can be more challenging in regard to both learning and testing, medical educators should create opportunities for interleaved learning instead of placing the onus on the learner. The shift from purely lecture-based education to interactive case-based education in both medical schools and residency programs creates opportunities to incorporate interleaving but doesn’t guarantee it.
When creating interleaved curricula, mastery of one subject or diagnosis is not required before moving on to learning a separate diagnosis. Trainees can begin learning about pneumonia and sepsis, then review acid-base disorders, and finally ventilator management. Then test their knowledge through an oral boards or simulation case that combines the recognition and application of these concepts.
The expectation of perfection can be detrimental; rather we should be sure to encourage this critical thinking and reinforce the connection between concepts whether their relation is obvious or more nuanced to our learners. Interleaving may be more challenging to learners but, with guidance, will create more permanent and deeper understanding of topics that can then be applied in the care of patients.
Driving it home
Interleaving, as a learning strategy, weaves together different yet related topics for studying across time.
Learning is most effective when it is effortful and active. The increased cognitive interference associated with interleaving of multiple topics simultaneously has been shown to improve comprehension, retention and test outcomes.
Given that learners frequently choose less effective study techniques, medical educators should create opportunities to incorporate interleaving into teaching curricula.
- Brown, P. C., Roediger, H. L., McDaniel, M. A., (2014) Make it stick. Cambridge, MA: The Belknap Press of Harvard University Press. Chapter 1, 15-17
- Birnbaum MS et al. (2013) Why interleaving enhances inductive learning: The roles of discrimination and retrieval. Mem Cogn. 41:392-402.
- Rohrer D et al. (2014) The benefit of interleaved mathematics practice is not limited to superficially similar kinds of problems. Psychon Bull Rev. 21:1323-1330.
- Taylor K and Rohrer D. (2010) The Effects of Interleaved Practice. Appl Cognit Psychol. 24:837-848.
- Tauber SK et al. (2013) Self-regulated learning of a natural category: Do people interleave or block exemplars during study? Psychon Bull Rev. 20:356-363.
- Bjork RA and Bjork EL. (2019). Forgetting as the friend of learning: implications for teaching and self-regulated learning. Adv Physiol Educ. 43(2):164-167.
- Nickson C. Learning by spaced repetition. Life in the Fast Lane blog. July 6, 2019. Accessed March 8, 2020. Available at: https://litfl.com/learning-by-spaced-repetition/
- Weinstein Y et al. (2018) Teaching the science of learning. Cogn Res Princ Implic. 3:2.
- Bjork, RA. (1994) Memory and metamemory considerations in the training of human beings. In J. Metcalfe and A. Shimamura (Eds.), Metacognition: Knowing about Knowing. (pp. 185-205). Cambridge, MA: MIT Press.
- Linderholm T et al. (2016) The benefit of self-testing and interleaving for synthesizing concepts across multiple physiology texts. Adv Physiol Educ 40:329-334.
- Rozenshtein A, Pearson GD, Yan SX, Liu AZ, Toy D. Effect of Massed Versus Interleaved Teaching Method on Performance of Students in Radiology.J Am Coll Radiol. 2016;13(8):979-984.
- Goldin SB, Horn GT, Schnaus MJ Jr, et al. FLS skill acquisition: a comparison of blocked vs interleaved practice. J Surg Educ. 2014;71(4):506-512.
- Monteiro S, Melvin L, Manolakos J, Patel A, Norman G. Evaluating the effect of instruction and practice schedule on the acquisition of ECG interpretation skills.Perspect Med Educ. 2017;6(4):237-245.
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