What Does Bilateral Stimulation Do to the Vividness and Emotion of a Memory?
One of the most distinctive features of Eye Movement Desensitization and Reprocessing (EMDR) is bilateral stimulation—stimulation that alternates from one side to the other while a person briefly brings a distressing memory to mind.
The best-known form is side-to-side eye movement, although alternating taps or tones are also used.
Researchers have spent years studying a basic question: does recalling a memory while doing a second task change how that memory feels when it is remembered again?
A substantial body of experimental research suggests that it can. In many studies, memories recalled while participants make eye movements later feel less vivid, less emotionally intense, or both than memories recalled without the added task. PubMed
That does not mean the memory disappears or that every form of bilateral stimulation works in exactly the same way. It means that the experience of recalling the memory can change.
What Do Researchers Mean by “Vividness”?
When researchers talk about the vividness of a memory, they are referring to how clear, detailed, immediate, or lifelike it feels when brought to mind.
A highly vivid memory may feel visually sharp and easy to picture.
A less vivid memory may still be completely recognizable, but it can feel more distant, less clear, or less visually intense.
This distinction is important because EMDR research does not generally suggest that bilateral stimulation erases autobiographical memories.
Instead, researchers often measure whether the memory feels different when recalled afterward.
In one early laboratory study, 60 healthy volunteers recalled emotional autobiographical memories while performing eye movements, finger tapping, or no additional task. Memories recalled during eye movements were later rated as less vivid than memories in the comparison conditions. Negative memories also became less negative in emotional tone. PubMed
This type of experiment helped establish one of the central findings in EMDR mechanism research: eye movements during recall can change the subjective quality of later recollection.
What Does “Emotionality” Mean in These Studies?
Researchers also commonly measure emotionality.
That usually means how emotionally intense or unpleasant a memory feels when the person recalls it.
Participants may be asked to rate questions such as:
How upsetting does this memory feel?
How emotionally intense is it?
How unpleasant is it to recall?
These ratings are usually collected before and after the experimental task.
If the memory remains recognizable but its emotional rating decreases, researchers describe that as a reduction in emotionality.
Several experimental studies have found reductions in emotionality after memory recall combined with eye movements. PubMed
Again, that does not necessarily mean the emotional meaning of the experience disappears. It means the memory may feel less emotionally charged when it is later brought to mind.
Do Vividness and Emotionality Change at the Same Time?
Not necessarily.
One particularly interesting study examined when these changes occurred during eye movements.
Participants recalled unpleasant autobiographical memories while either making eye movements or keeping their eyes still.
The researchers found that vividness decreased very quickly—within the first few seconds—while emotionality took considerably longer to decrease. In that study, the significant change in emotionality appeared only after a longer period of eye movements. PubMed
That finding suggests that vividness and emotionality may be related but are not identical.
One possible sequence is that a memory first becomes less vivid and that the emotional intensity then decreases afterward.
That interpretation fits with some working-memory explanations of EMDR, although it remains a theory rather than a complete explanation of the treatment.
Why Might Eye Movements Change a Memory?
One of the leading explanations involves working memory.
Working memory is the limited mental system used to hold and manipulate information temporarily.
Remembering a vivid emotional event uses some of that capacity.
Making rapid eye movements also requires attention and working-memory resources.
If both tasks are performed at the same time, they may compete for the same limited mental capacity.
The theory is that this competition makes it harder to hold the memory in exactly the same vivid and emotionally intense form while it is being recalled.
When the memory is stored again after that disrupted recall, it may later feel less vivid or emotionally charged.
Experimental studies support parts of this explanation.
For example, research has found that eye movements can reduce vividness and emotionality more than simply recalling the memory alone, and that the effect appears when the memory is actively held in mind during the eye movements. PubMed
Does the Memory Actually Change?
This is a more complicated question.
Researchers can measure how vivid or emotional a memory feels, but that is not the same as proving that every aspect of the underlying memory has been permanently altered.
A 2014 study examined whether reductions in vividness and emotionality persisted after 24 hours.
Participants recalled negative autobiographical memories either with or without eye movements. The researchers found immediate reductions in vividness after eye movements, and with the longer eye-movement condition, reductions in both vividness and emotionality were still present at the 24-hour follow-up. PubMed
That suggests the effect can last beyond the moment the eye movements are occurring.
More recent research has also replicated the general finding that eye movements can reduce the experienced vividness and emotionality of unpleasant autobiographical memories. PubMed
At the same time, researchers remain careful about what this means.
A memory becoming less vivid does not necessarily mean its factual content has been removed.
Does Bilateral Stimulation Change What People Remember?
The evidence here is less clear.
Researchers have asked whether eye movements alter not just vividness and emotion, but also the number or type of details people remember.
A 2024 replication study tested whether eye movements changed the content of unpleasant autobiographical memories.
The researchers replicated the finding that memories became less vivid, and in one of the experiments less emotional, after eye movements compared with simple recall.
However, they did not find clear evidence that eye movements changed the number of central or peripheral details people reported. PubMed
That distinction is useful.
The strongest experimental findings concern how the memory is experienced, particularly its vividness and emotional intensity.
Evidence that bilateral stimulation systematically changes the actual factual content of memory is much less clear.
Are Eye Movements the Only Kind of Bilateral Stimulation That Has Been Studied?
No, but eye movements have received much more experimental attention than some other forms of bilateral stimulation.
Alternating tapping, sounds, and vibration are also used.
Research comparing different tasks suggests that what matters may not simply be movement from left to right, but whether the additional task places enough demand on working memory while the memory is being recalled.
For example, one study compared eye movements with finger tapping and a no-movement condition. Eye movements produced stronger reductions in vividness than tapping. PubMed
Other experiments have found that tasks that interfere with the same sensory system as the memory can sometimes have stronger effects.
For primarily visual memories, eye movements may interfere more with vividness than tasks that use verbal processing. PubMed
This is one reason researchers continue studying the mechanisms rather than assuming that every form of alternating stimulation has exactly the same effect.
What About Tapping, Tones, or Vibration?
The evidence for other forms of bilateral stimulation is more mixed.
A 2026 experimental study tested alternating vibratory bilateral stimulation while participants recalled negative autobiographical memories.
The vibration prevented the increase in emotional intensity that occurred during recall without stimulation, but it did not significantly reduce vividness. The more distracting participants found the vibration, the greater the reduction in emotionality. PubMed
That finding is interesting because it suggests different forms of stimulation may affect memory experience in somewhat different ways.
It also supports the idea that the cognitive demand of the additional task may matter.
However, one recent experiment is not enough to conclude that vibration, tapping, eye movements, and tones are interchangeable.
A later article in this series, Eye Movements, Tapping or Tones: What Has Research Actually Studied?, examines those differences more directly.
Does the Memory Need to Be Recalled During the Stimulation?
Research suggests that it does matter.
One experiment found that eye movements reduced vividness and emotionality only when participants were actively recalling the unpleasant memory during the movements. PubMed
That result fits with the working-memory explanation.
The theory depends on two things happening at once:
the memory is active in working memory;
another task is competing for some of the same mental resources.
Simply moving the eyes without recalling the memory would not create the same competition.
This helps explain why bilateral stimulation is paired with memory recall within EMDR rather than being treated as a separate activity.
Does a Bigger Mental Load Always Produce a Better Effect?
Not necessarily.
Working-memory research suggests there may be an optimal level of competition.
If the second task is too easy, it may not interfere much with the memory.
If it is too difficult, a person may no longer be able to keep the memory in mind well enough for the process to work as intended.
Researchers have therefore investigated the idea of matching task difficulty to working-memory capacity.
This is still an active research area, but it helps explain why simply making bilateral stimulation faster or more complicated would not automatically be expected to make EMDR more effective.
More is not necessarily better.
Does Reduced Vividness Automatically Reduce Emotion?
Often the two change together, but not always.
The study examining the time course of eye movements found that vividness decreased before emotionality. PubMed
Other studies have found reductions in vividness without an immediate reduction in emotionality, or vice versa. PubMed
This tells us that vividness and emotion are related but separable features of memory.
A memory can become less visually sharp before it feels less upsetting.
It can also become less emotionally intense without showing a large measured change in vividness.
The exact relationship between those changes is still being studied.
Are These Laboratory Studies the Same as Full EMDR Therapy?
No.
This is an important distinction.
Many experiments studying vividness and emotionality use healthy volunteers recalling unpleasant autobiographical memories for a relatively short period.
That is not the same thing as receiving a complete course of EMDR.
Full EMDR is a structured treatment that includes several phases. Bilateral stimulation is one component within that larger process.
Laboratory experiments are useful because they allow researchers to isolate one element—such as eye movements—and study what it does under controlled conditions.
They can help explain how part of EMDR may work.
They do not reproduce every part of the therapy.
What Do These Findings Tell Us About EMDR?
The laboratory evidence helps answer one specific question:
What happens to a memory when someone recalls it while performing a competing bilateral or dual-attention task?
Across many studies, eye movements during recall have been associated with reductions in memory vividness, emotionality, or both. PubMed
The findings are broadly consistent with the idea that competing working-memory demands can change the way a memory is experienced.
But researchers have not shown that all bilateral stimulation methods work identically, nor have they completely settled why these effects occur.
The evidence is therefore strongest for a narrower conclusion:
Recalling an unpleasant memory while performing eye movements can make later recollection feel less vivid and, in many studies, less emotionally intense.
Frequently Asked Questions
Does bilateral stimulation erase a memory?
No. Research generally examines changes in how vivid or emotionally intense a memory feels. People still remember the event. The evidence does not suggest that eye movements simply delete autobiographical memories.
Do eye movements make memories less vivid?
Many experimental studies have found that memories recalled during eye movements are later rated as less vivid than memories recalled without the eye movements. PubMed
Does the emotional intensity of a memory decrease too?
Often, yes. Several studies report reductions in emotionality, although vividness and emotional intensity do not always change at exactly the same time or to the same degree. PubMed
Do tapping and vibration work exactly like eye movements?
The research does not support assuming that all forms are identical. Eye movements have been studied more extensively. Some newer research suggests vibratory bilateral stimulation may reduce emotional intensity without producing the same reduction in vividness. PubMed
Why might bilateral stimulation affect a memory?
One leading explanation is that recalling the memory and performing another attention-demanding task compete for limited working-memory resources. This competition may make the memory less vivid and emotionally intense when it is recalled again. PubMed
Conclusion
Research on bilateral stimulation gives us a clearer picture of what may happen to a memory during one important part of EMDR.
When people recall an unpleasant autobiographical memory while making side-to-side eye movements, the memory often becomes less vivid, less emotionally intense, or both when it is recalled afterward.
Experimental studies suggest that vividness may decrease before emotionality and that some changes can still be detected after the eye movements have ended. PubMed
The most established findings concern eye movements. Other forms of bilateral stimulation, including tapping, tones, and vibration, have been studied less extensively and may not produce exactly the same effects.
Researchers are still working out the precise mechanism. The working-memory explanation has substantial experimental support, but it remains one part of a larger scientific discussion about how EMDR works.
What the research does support reasonably well is this:
Bilateral or dual-attention tasks—especially eye movements—can change the subjective experience of recalling an unpleasant memory, making it feel less vivid and often less emotionally intense without erasing the memory itself.
