Lag Effect

If we are not aware of the lag effect, we could use methods for retaining information that are not effective. Many learning and studying techniques fail to take the lag effect into consideration.

For example, “cramming”, where we quickly and repeatedly review information right before an exam, often involves successive repetition. Unfortunately, we quickly forget the information that we “crammed.” 

Not knowing about the lag effect can also cause us to make decisions in our daily lives that lead to forgetfulness. We may think that if we have to remember 21 grocery items, it is easier for us to split the list into three shorter lists with seven items each and repeat each small list a few times before moving on to the next one. However, this reduces the time between the repetition of information, as you would encounter the first grocery item after only six other words instead of 20 other words. According to the lag effect, such a technique would make you less likely to remember the grocery items later. 

Since we are expected to remember information both in our personal and professional lives, not being aware of the ways in which our brains retain information can cause us to have sub-optimal memory. 

Although individually, we can try to space out repetitions of information in order to activate the lag effect, often, the way that information is taught or presented to us is not under our control. 

It may seem more intuitive that if we repeat the information right away, it is more likely to be encoded to memory. However, by being aware of the lag effect, educators can ensure they leave enough time between repetitions so as to give their students the best shot at committing it to memory. Teachers can space out review sessions or combine the information that people need to remember with other activities so as to increase the lag between repetitions.

There are two prominent explanations that have been proposed for why the lag effect happens. 

The first suggests that the more time that passes between repetitions of information, the more likely we are to encode and contextualize it in a different manner.¹ Since the repetitions are represented differently in our minds, we have a better shot of remembering it later because we can remember either of the representations.

For example, the first time we encounter the word “garden” we may associate it with growing vegetables. Then we look at other words like “concert” or “gathering”, and when “garden’ is repeated again, we might think of Madison Square Garden. By encoding the information with two different associations, we may be more likely to remember it later, because we can remember either growing vegetables or Madison Square Garden.

This is known as the “contextual variability account” and is thought to be a cause for the lag effect.¹ This account may also provide evidence of the levels of processing effect, which suggests that when information is encoded on a deeper level, we are more likely to remember it at a later date. Information that is encoded in two different ways may be encoded on a deep level through multiple semantic associations. 

The second explanation, the “deficient processing account”, presumes that the lag effect occurs because we are unable to encode the second repetition of information at the same level as the first presentation of information if the repetitions are too close together.² Deficient processing might occur because we are habituated to the information, or because we are less likely to pay attention to the repeated information when it closely follows the first presentation because our brains think we have already registered the information.

The lag effect has consequences in our educational, professional, and personal lives. We constantly are presented with information that we need to remember. That could be in the form of having to remember 20 French words for an exam, having to remember the data we need for a presentation, or having to remember to pick up the dry-cleaning. Regardless of the context, having a good memory is a vital component of everyday life.

Since the lag effect can impact whether we remember information, we need to make sure we understand how our brains and memories work. By knowing about the lag effect, we can ensure that we allow more time to pass before we re-examine or repeat the information that we are trying to remember. Using techniques that activate the lag effect means that we can become more efficient when it comes to committing information to memory. 

Since the lag effect is a positive cognitive bias that helps us better remember information, we want to take it into account for our learning and studying techniques. According to the lag effect, in order to improve our memory recall, we should leave more time in between repetitions of information. 

Repetition is still important for retaining information, but successive repetition is not the most effective way to learn. Instead, there should be lags between repetitions. Lags can be increased by spacing out study sessions or by interspersing the information you are trying to remember with other material.

The lag effect is associated with the spacing effect, which suggests learning is more efficient when study sessions are spaced out than when sessions are successive. The lag effect takes the spacing effect a step further, saying that the longer the time between spaced out study sessions, the better performance will be.

In 2005, Dr. Michael Kahana, an influential behavioral psychologist, wanted to examine whether the longer the ‘lag’ between learning sessions, the better information would be recalled.¹

In order to examine whether the time between learning sessions affected recall, Kahana conducted a study where participants were presented with lists of words that were repeated multiple times. Participants were later asked to recall the words they had seen. Participants were split into three groups, each with a different ‘lag’. The first group, called the “massed” group, saw each word repeated three times successively. The second group, the “spaced-short” group, saw each word with two-to-six other words in between before they encountered a repeated word. The last group, the “spaced-long” group, saw each word with six-to-twenty words in between before they encountered a repeated word. 

Kahana found that recall improved the longer the lag was between repetition of words. The recall from participants in the spaced-long condition was 15% better than recall for participants in the massed condition.¹ While the spacing effect describes how we better retain information when there is a space between presentation of that information, this experiment showed that the length — or the lag — of that space also has an impact on memory. 

Educators are often under great time constraints, having limited time in which they need to ensure students learn the necessary material. As a result, they may be unable to spend multiple sessions repeating information.

Dr. Carolina Küepper-Tetzel, an expert in examining how our cognitive processes impact learning, recognized the difficulty educators face.³ She wanted to assess when the most effective time would be for repetition to occur, so educators could manage their time most effectively. To determine the best method for repeated learning, she examined how lag effect impacted classroom learning of vocabulary.

To test the lag effect, she conducted an experiment with 65 German-speaking sixth graders. The students were all taught 26 English-German vocabulary pairs in an initial session where they were not allowed to take notes, in order to isolate the lag effect as the only technique influencing recall. Students then either had a follow up review session the same day as the initial session (0-day lag group), one day after the initial session (1-day lag group) or 10 days after the initial session (10-day lag group). To end the experiment, students either took an exam either seven or 35 days after their last learning session.

Dr. Küepper-Tetzel found that for the students that took the exam seven days after their last learning session, the ideal lag time was one day, as students in the 1-day lag group had the best recall of the German-English pairs. However, for the students that took the exam 35 days after their last learning session, both the 1-day lag group and 10-day lag group did significantly better than the 0-day lag group. From these results, Dr. Küepper-Tetzel concluded that the optimal length of time for teachers to repeat information to students is likely between one and ten days.³

This study demonstrates that immediate repetition is the least effective way for teachers to ensure their students are retaining information, and that they should leave at least one day in between repetitions. It also suggests that the lag effect is more prominent the further away the exam is, suggesting the lag effect has a greater impact for long-term memory. 

There are many studies that have provided evidence that the lag effect exists, but fewer that have tried to pinpoint the mechanics behind the lag effect. A PhD student, Natalie Koval, with an interest in how the lag effect impacts second-language learning, wanted to better understand the deficient processing account that is thought to be behind the lag effect.⁴ She was especially interested in the deficient processing account because attention is thought to be an important factor in second-language vocabulary acquisition.

Koval split her participants into a massed condition group, where participants saw novel Finnish words repeated in four consecutive sentences, and a space condition group, where the novel Finnish words were only repeated after 25 other sentences had been read. Participants were in control of moving on to the next word with a space bar. While participants completed the task, their eye movements were recorded with a special tracker. 

Koval found that the total reading time for the massed condition group was lower than the total reading time for the spaced condition group. This demonstrated that overall, less attention is paid to information when there is repeated successive exposure to it. Additionally, the eye movements recorded showed that gaze duration decreased for both groups for any subsequent repetition, but much more drastically for the massed condition group.⁴

These findings suggest that one of the reasons behind the lag effect is that we actually spend less time processing information that we have just seen, perhaps because our brains think that we have already processed it. This cognitive mistake provides a barrier to second-language acquisition, as Koval found that participants had worse recall of the Finnish words when they had been in the massed condition than when they had been in the spaced condition. 

What it is

The lag effect describes the likelihood that we will better recall information when time between repeated exposure to that information increases. The lag effect demonstrates that successive repetition is not the most effective way to retain information. 

Why it happens

There are various theories as to why the lag effect happens. Two of the most prominent ones are the contextual variability account and the deficient processing account. 

The contextual variability account describes the fact that when repetition of information is further apart, we are more likely to contextualize and encode the information differently each time. Since we have multiple associations formed with the information, it may be easier for us to remember.

The deficient processing account suggests that the lag effect occurs because we are worse at encoding information that we have just been exposed to. This may be because we pay less attention when something is immediately repeated than if it is repeated after a lag. 

Example 1 – The lag effect has a greater impact on long-term recall

Teachers need to be aware of the lag effect in order to manage their time most effectively by repeating information after the most optimal lag for the best test scores. If information needs to be recalled soon, a one-day lag between repeating information to students may be the most optimal, but when a test is being taken much later, the longer the lag between study sessions, the better the test scores. 

Example 2 – The lag effect may be caused by reduced attention

The lag effect is thought to occur in part because of the deficient processing account. The deficient processing account is a barrier to learning second-language vocabulary, because it leads us to spend less time reading and encoding information when it is repeated immediately. When less attention is paid to information, we are less likely to commit it to memory.

How to activate it

The lag effect can be activated by avoiding studying techniques that involve immediate successive repetition, such as cramming. Instead, we should use techniques that space out the time between the repetition of information. An easy way to activate the lag effect is to space out our study sessions over multiple days.