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Spacing effect

Dr. Simon Moss


At school or university, students need to learn a diversity of topics and subjects. Some students confine the study of some topic or subject to a limited time. They might, for example, study one subject only during the first week of April and then study another subject only during the second week of April--an approach called massed learning. In contrast, other students tend to distribute their attempts to learn each topic or subject over a more extended time. For instance, during the first week of April, they might study all of their topics and subjects. During the second week of April, they might review these topics and subjects again. This approach is called spacing or spaced learning.

The key finding, substantiated in a multitude of studies, is that spacing is more effective than massing (e.g., Cepeda, Pashler, Vul, Wixted, & Rohrer, 2006& Rohrer & Taylor, 2006, 2007). That is, relative to their peers, students who distribute the time they devote to each topic over an extended period tend to perform more effectively on subsequent exams or tests.

Empirical evidence

Many paradigms have been utilized to verify the spacing effect. A typical study was conducted by Kornell (2009). In this study, participants were exposed to a series of 20 cards. On each card was a pair of synonymous words, such as effulgent and brilliant. The first word was unfamiliar to most participants, whereas the second word was generally familiar.

For some of the participants, a sequence of five cards were first presented four times. Then, the next sequence of five cards was presented four times. The same procedure was applied to the two other sets of five cards. This protocol resembles massed learning: Each card was studied within a limited time.

For the other participants, all 20 cards were presented in sequence, four times. This protocol resembles spacing: Each card was presented early and late in the session. Apart from this difference, the two conditions were identical. That is, each card was presented four times. The time that was granted to study each card was unlimited.

After they studied the cards, their learning was tested. A multiple choice test was administered to assess whether participants learnt the unfamiliar terms. If participants were exposed to the spacing rather than massing protocol, their responses were more likely to be accurate.

A subsequent study, reported by Kornell (2009), generated similar results. In this study, in the spacing condition, learning of each item was distributed across distinct sessions rather than different times within the same session. In the massed condition, learning of each item was confined to a specific session. The pattern of results was the same, however: performance on a subsequent exam was more proficient when a spacing, rather than massed, approach was applied.

Mechanisms that underpin the spacing effect

Variability in cues and contexts

Several explanations have been proposed to accommodate the spacing effect. According to the first explanation, when a spacing protocol is applied, each item, concept, or fact to learn coincides with a variety of contexts. When each item is associated with a diversity of contextual cues, memory is enhanced (cf., Glenberg, 1979& Greene, 1989).

Suppose, for example, that students learn the same fact during distinct months. During the first month, they might be living at home, with their parents, feeling anxious by the scope of this course. During the second month, they might have shifted, to an apartment, but become more confident. As a consequence, they associate this fact with a diverse array of cues: their home, the apartment, anxiety, and confidence. If any of these cues or concepts are incidentally evoked during the exam, they become more likely to remember the fact, and their performance on this exam thus improves.

In contrast, if students learn this fact during a specific context only, the fact is not associated with a broad array of cues. The fact is less likely to be retrieved during an examination.


When the spacing protocol is applied, the items, when studied, are not especially salient or accessibility. More cognitive processes need to be applied or executed to retrieve these facts. These processes ensure the memory traces of these facts are more sustainable (Bjork & Bjork, 1992).

To illustrate, consider students who attempt to learn some fact, such as the first sequence of ten elements, one hour a month, over the semester. Each time they consider these elements, they have not studied this information for a month or so. The elements are not especially accessible but seem hazy. The students, therefore, must apply a diverse set of cognitive operations to remember these elements. They might, for example, attempt to remember the location in which they last studied these names. They might strive to recall various properties of these elements, and so forth.

These cognitive operations can enhance subsequent learning and memory. These operations afford students with more opportunities to retrieve these elements in the future (see also Appleton-Knapp, Bjork, & Wickens, 2005& Cuddy & Jacoby, 1982).


A similar, but distinct, explanation is that students devote more effort to the items when they apply a spacing protocol (see Greene, 1989). In particular, when students apply a massing protocol, they are exposed to the same item or fact, several times, within a limited timeframe. These items or facts seem increasingly familiar on each occasion. Accordingly, after each exposure, students dedicate less effort to learning the item. The aggregate level of effort declines, and thus learning tends to dissipate.

Several studies have uncovered results that substantiate this explanation. Pupil dilation, which represents level of effort, diminishes when participants are exposed to some stimulus more than one time--but only when a massed rather than spaced protocol is applied (e.g., Magliero, 1983).

Determinants of accessibility or effort

Challis (1993& see also Russo & Mammaralla, 2002) has clarified this account. This clarification refers to the mechanism of semantic priming. In particular, when individuals read a word, they become more sensitive to other terms with related meaning. After they read the word doctor, they can more rapidly recognize related terms such as nurse. They can also recognize the same word, doctor, more rapidly.

Accordingly, when individuals process the meaning of one item, they become more sensitive to a subsequent exposure of this item. Hence, the second exposure of this item demands less extensive processing.

When the items are distributed over time, however, semantic priming declines. That is, exposure to some item will not facilitate recognition of the same item presented after a significant delay. Accordingly, when the spacing protocol is applied, individuals still need to process subsequent exposure to the item extensively, which facilitates later recognition or recall. Consistent with this approach, the spacing effect can be maintained even if individuals do not attempt to remember the words--provided they are encouraged to process the meaning, and not merely the form, of these items (Challice, 1993).

This account, however, has been challenged. In particular, studies indicate the same effect persists if the items are unfamiliar stimuli, such as faces, rather than meaningful words (e.g., Russo, Parkin, Taylor, & Wilks, 1998& Mammarella, Russo, & Avons, 2005). Conceivably, when the stimuli are unfamiliar, items with a similar pattern or structure are subsequently recognized more rapidly--a form of repetition priming that is dependent upon perception rather than meaning. This priming is limited when items are spaced across time& these items thus demand more extensive processing. Interestingly, even shifting the orientation of these patterns has been shown to curb the benefits of spacing (Mammarella,Russo, & Avons 2002).

Multiple processes

Many researchers argue that several mechanisms could underpin the spacing effect--and the impact of each mechanism could vary across conditions (e.g., Greene, 1989). To illustrate, Greene argued the diversity of cues that are associated with each item, particularly when the learning is spaced, can facilitate recall.

Nevertheless, this mechanism, according to Greene (1989) might not be as applicable when participants merely need to recognize whether or not some item was presented. The decision as to whether some item has been presented earlier is less contingent upon the variety of contexts or cues. Instead, spacing might increase the level of effort that individuals devote to items. That is, when learning is spaced over time, participants feel they need to rehearse more vigorously to retain items--which can then facilitate subsequent recognition. Consistent with this proposition, when individuals are not informed they will need to remember the items later, the benefits of this spaced approach declines, presumably because effort is not devoted to this task.

Characteristics of tasks or individuals that determine whether spaced or massed learning is preferable

Experiential learning versus verbal learning

As Lakshmanan, Lindsey, and Krishnan (2010) showed, spaced learning is not always more effective than massed learning. In particular, if participants strive to learn verbal principles, spaced learning is often preferable. However, if participants attempt to develop a skill by practicing extensively, massed learning may be more effective.

Lakshmanan, Lindsey, and Krishnan (2010) conducted a series of four experiments to assess and clarify this possibility. In the first study, participants learnt to use software that is designed to record, modify, and organize music. Their main task was to import and change the format of music recordings, partly to increase the availability of memory space.

Some participants were encouraged to learn verbal principles. They received instructions on how to utilize the software but negligible time to practice. Other participants were encouraged to learn experientially. That is, they were granted only limited time to read the instructions but more time to practice using the software.

In addition, spaced learning was enforced on some participants. That is, while developing their capacity to learn the software, various questions, about the restaurants or movies that participants like, were interspersed. Massed learning was enforced on other participants. Specifically, these questions were asked before participants learnt the task.

As hypothesized, if verbal learning was encouraged, spacing tended to be effective: That is, participants learnt to complete specific tasks, such as importing and changing the format of music recordings, more expeditiously. Conversely, if experiential learning was encouraged, massed trials were more effective.

In Study 2, participants completed a task that demanded only experiential, rather than verbal, learning. In this study, they learnt a different software package, also intended to modify music files. To learn the software, participants completed a task in which they changed the default volume of a music file. Then, to assess their capacity to transfer this learning to other tasks, participants completed an activity in which they introduced a gradual fade or decline in volume towards the end of these music files. The two tasks demanded the selection of different options but the same overall menu. Finally, participants also expressed the thoughts they entertained while they completed these tasks& otherwise, the procedure was similar to Study 1.

If the learning was massed rather than spaced, participants transferred their learning from one task to the other task more effectively. That is, they could introduced a gradual fade more efficiently. Furthermore, massed learning increased the likelihood that participants alluded to more abstract concepts, instead of only tangible actions, while expressing their thoughts.

Study 3, in contrast to Studies 1 and 2, examined the effect of learning schedules on quality of performance rather than merely time to complete some task. Participants learnt the same software that was used in Study 1 but needed to complete different tasks. The participants first learned how to construct a unique file, demanding verbal learning. The participants were later tested on a task in which a file was converted to a ringtone. Furthermore, participants were instructed to draw boxes and arrows to represent their understanding of how the software can be used to create the unique clips.

In this instance, massed learning, compared to spaced learning, on the first task enhanced performance on the second task. Presumably, massed learning was less likely than spaced learning to facilitate the formation of memory on the first task. Consequently, individuals were not as distracted by these memories when they attempted the second task. Massed learning also increased the conceptual understanding of participants, as distilled from the boxes and arrows. Finally, Study 4 showed that massed learning may not only enhance performance on experiential tasks but could also promote more positive attitudes.

In short, spaced learning can facilitate memory of verbal information or principles, consistent with the spacing effect. Massed learning, however, seems to enhance the capacity of individuals to unearth broad concepts about the relationships between distinct features, facets, or actions in a task--vital for complex activities. That is, when learning is massed, individuals are more able to contrast their experiences across consecutive attempts, uncovering key insights.

Practical implications

Despite the ubiquity of this spacing effect, many students assume that massed study is more effective (e.g., Salisbury & Klein, 1988& for factors that moderate this effect, see Benjamin & Bird, 2006& Son, 2004). In the study conducted by Kornell (2009), for example, participants were asked to predict their level of performance on a subsequent memory test. Participants anticipated they would perform more proficiently if they had been assigned to the massed, rather than spacing, condition. Students, therefore, tend to predict that massed exposure to items should facilitate learning.

This misconception might arise because individuals, when subjected to a massed presentation of items, feel the task is easier (Baddeley & Longman, 1978). That is, an item or fact, when presented several times during a limited duration, seems very familiar. As a consequence, participants feel they have learnt these items or facts proficiently. They overestimate the likelihood they will be able to retrieve this information in a subsequent exam.

Related strategies

Personalized review

Even if students do distribute their learning over time, some key decisions need to be reached. To illustrate, suppose students need to learn 10 chapters of a book--one chapter a week for 10 weeks. They could apply a variety of strategies. At the end of each week, they could review only one chapter, such as the chapter they learned that week. Or, they could review the chapter they learned that week and the chapter they learned the week before, and so forth.

Lindsey, Shroyer, Pashler, and Mozer (2014) uncovered a strategy that seems to be most effective. In essence, they should review the material that is least prominent in their memories.

Specifically, in this study, Spanish students needed to learn one chapter a week over 10 weeks on learning English. Each week comprised three half hour sessions, in which students learned English words and phrases, reviewed the material, and then received an exam on that chapter. They also received an exam one month later.

Participants were assigned to one of three conditions. Which words or phrases could be reviewed varied across the conditions. In the first condition, participants could merely review the items they learned that week, similar to massed practice. In the second condition, participants could review items they learned that week and the previous week. In the final condition, participants reviewed items that were least prominent in their memory. A Bayesian model was utilized to predict which items would be most prominent in memory, based on performance of this student, and other students, with these items on previous exams. In general, performance on this exam a month later was better if students reviewed items that were not as prominent in memory.


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Last Update: 7/5/2016