Eye Movements, Tapping or Tones: What Has Research Actually Studied?
Eye Movement Desensitization and Reprocessing (EMDR) is best known for the side-to-side eye movements used while a person briefly recalls a distressing memory. But eye movements are not the only form of alternating stimulation used in EMDR.
Alternating taps, sounds or tones, and vibrating devices may also be used. Collectively, these are often described as bilateral stimulation—stimulation that alternates from one side of the body or sensory field to the other.
It can be tempting to assume that eye movements, tapping, and tones are simply three equivalent versions of the same thing.
The research is more complicated.
Eye movements have been studied much more extensively than other forms of bilateral stimulation. Tapping and auditory tones have also been tested, but fewer studies have examined them directly, and some experiments suggest they may not affect memory in exactly the same way or to the same degree. Frontiers
Understanding those differences helps clarify what scientists actually know—and what remains uncertain.
What Is Bilateral Stimulation?
Bilateral stimulation means stimulation that alternates between the left and right sides.
During EMDR, this may involve:
following a moving target from side to side with the eyes;
alternating taps on the hands, knees, or another part of the body;
listening to sounds that alternate between the left and right ears;
or using devices that alternate gentle vibration between the hands.
The U.S. Department of Veterans Affairs National Center for Posttraumatic Stress Disorder (PTSD) describes several ways bilateral stimulation can be delivered, including therapist-guided eye movements, light bars, tactile devices, self-tapping, and alternating auditory tones. VAntage Point
In practice, several methods therefore exist.
In research, however, they have not all received the same amount of attention.
Eye Movements Have Been Studied the Most
The strongest experimental literature concerns side-to-side eye movements.
Researchers have repeatedly asked people to recall unpleasant or emotionally meaningful memories while making eye movements and then rate how vivid and emotional those memories feel afterward.
Across many studies, memories recalled during eye movements have later been rated as less vivid, less emotionally intense, or both compared with memories recalled without the additional task. PubMed Central (PMC)
A major systematic review of proposed EMDR mechanisms examined 87 studies and found that eye movements were the most frequently studied form of bilateral stimulation. The review found reasonable empirical support for the working-memory explanation of EMDR, while also emphasizing that the mechanism is not completely settled. Frontiers
This makes eye movements the form of bilateral stimulation for which researchers currently have the most detailed experimental evidence.
Why Have Researchers Focused So Much on Eye Movements?
Part of the reason is historical: eye movements were central to the original development of EMDR.
But they are also convenient for experimental research because researchers can control factors such as:
speed;
duration;
direction;
visual tracking;
and whether participants move their eyes or keep them still.
This makes it easier to isolate the effect of the eye movements from simple memory recall.
Researchers have also been able to measure how cognitively demanding the eye movements are.
One study involving 108 participants found that recalling an unpleasant autobiographical memory while performing eye movements reduced vividness and emotionality more than recalling the memory without eye movements. The findings supported the idea that both memory recall and eye movements compete for limited working-memory resources. PubMed Central (PMC)
This type of study helps researchers investigate why eye movements may influence the experience of a memory.
What Has Research Found About Tapping?
Tapping has been studied, although not nearly as extensively as eye movements.
Some early experiments compared eye movements with spatial or finger-tapping tasks.
A well-known series of working-memory experiments by Andrade and colleagues found that both eye movements and certain tapping tasks could reduce the vividness and emotional impact of mental imagery compared with doing no additional task. The researchers proposed that both tasks competed with the mental resources needed to hold the image clearly in mind. Frontiers
This finding is important because it suggests that eye movement itself may not be the only task capable of changing memory vividness.
Other cognitively demanding tasks have also produced similar experimental effects, including complex drawing, mental arithmetic, and computer-based tasks. PubMed Central (PMC)
That supports one of the leading scientific explanations of EMDR: what matters may be partly the competition created when a person recalls a memory while simultaneously performing another demanding task.
However, that does not mean every tapping procedure is equally effective.
The amount of mental effort required by the tapping task appears to matter.
Simple Tapping and Complex Tapping Are Not Necessarily the Same
The word “tapping” covers several different procedures.
A simple repetitive tap may place very little demand on attention.
A more complex spatial tapping pattern may require considerably more concentration.
That distinction matters under the working-memory explanation.
If the benefit comes partly from dividing limited attention between memory recall and another task, a very easy task may not compete strongly enough with the memory to produce the same effect as a more demanding one.
Research reviewed in the EMDR mechanism literature has found that complex tapping and other demanding secondary tasks can reduce memory vividness or emotionality. But simpler tapping tasks have not always produced effects as large as eye movements. Frontiers
So the research does not support a simple statement such as “tapping works exactly the same way as eye movements.”
It suggests instead that the characteristics of the task matter.
What About Alternating Tones or Beeps?
Auditory stimulation has also been studied.
In these procedures, sounds alternate between the left and right ears while the person recalls a memory.
One laboratory study compared alternating auditory beeps with eye movements and found that both could affect negative memories, but the effects were larger for eye movements. The researchers concluded that the auditory tones placed less demand on working memory than eye movements did. Frontiers
Another study involving people with PTSD directly compared tones with eye movements during EMDR. Eye movements produced larger reductions in the vividness and emotionality of trauma memories than tones. emdr.com
Interestingly, participants' subjective preferences did not necessarily match those experimental results. In that study, people sometimes perceived tones as effective even though the measured reductions in memory vividness and emotionality were greater with eye movements. emdr.com
That is a useful reminder that what feels preferable and what produces the largest laboratory effect are not always the same question.
Does That Mean Tones Do Nothing?
No.
Some studies have found that tones or beeps affect memory more than simply recalling the memory without any additional task.
But their effects have often been smaller than those produced by eye movements.
The 2018 systematic review of EMDR mechanisms summarized research in which tones reduced memory vividness but were less effective than eye movements. Frontiers
This fits with the working-memory explanation.
If an auditory task requires some attention, it may compete with memory recall. If it requires less attention than rapid eye movements, however, the effect may be smaller.
That is a more accurate interpretation than saying tones either “work” or “do not work.”
Does Bilateral Alternation Itself Matter?
This is one of the more interesting scientific questions.
Originally, EMDR theories often emphasized the left-right alternating nature of the stimulation itself.
But working-memory research has complicated that picture.
If bilateral alternation were the essential mechanism, we would expect left-right stimulation to have a unique advantage over non-bilateral tasks.
Instead, researchers have found that several tasks that are not inherently bilateral can also reduce memory vividness and emotionality if they compete strongly enough for working memory. These include mental arithmetic, complex drawing, and other attention-demanding tasks. PubMed Central (PMC)
That does not prove that bilaterality has no role.
It does mean that the scientific explanation cannot simply be:
“Alternating left and right is what makes the memory change.”
The available evidence suggests the process may depend more broadly on dual attention and cognitive load, although researchers continue to study other possible mechanisms. Frontiers
What Does Working-Memory Theory Predict?
The working-memory theory of EMDR starts with a simple idea.
Working memory has limited capacity.
Recalling a vivid emotional memory requires some of that capacity.
Performing another demanding task at the same time also requires some.
When the two tasks occur together, they compete.
The memory may therefore be held less clearly in mind and may later feel less vivid or emotionally intense.
Research supports several predictions from this theory.
Eye movements place a measurable demand on working memory, and studies generally find that more demanding dual tasks can produce larger reductions in vividness and emotionality than easier tasks. PubMed Central (PMC)
This helps explain why eye movements, complex tapping, arithmetic, and other tasks can sometimes produce similar kinds of effects even though they look very different.
The previous article in this series, What Does Bilateral Stimulation Do to the Vividness and Emotion of a Memory?, examines those memory changes in more detail.
Does Faster or Harder Always Mean Better?
Not automatically.
If the secondary task is too easy, it may place too little demand on working memory.
But if it is extremely demanding, it could become difficult to keep the memory in mind at all.
Researchers have therefore explored whether there may be an effective level of cognitive load between those extremes.
Studies manipulating eye-movement speed have found that faster movements can sometimes produce larger reductions in vividness and emotionality, supporting the general idea that cognitive load matters. But attempts to precisely match eye-movement speed to an individual's working-memory capacity have not consistently produced the predicted results. PubMed Central (PMC)
So there is no research basis for simply assuming that faster, stronger, or more complicated stimulation is always better.
Are Laboratory Studies the Same as EMDR Therapy?
No.
Many studies comparing eye movements, tapping, and tones are laboratory experiments, not full courses of EMDR treatment.
Participants may be healthy volunteers who bring an unpleasant autobiographical memory to mind for a few minutes while researchers manipulate one specific variable.
That approach is useful because it isolates the component researchers want to study.
But full EMDR is a structured therapy involving multiple phases and procedures. Bilateral stimulation is one component within that broader treatment.
A laboratory finding that eye movements reduce memory vividness therefore tells us something important about a possible mechanism.
It does not by itself tell us that replacing eye movements with a particular tapping or auditory procedure will produce identical clinical outcomes over a complete course of EMDR.
This distinction is especially important when comparing different forms of stimulation.
Have Clinical Studies Compared the Different Forms Directly?
Some have, but there are fewer direct clinical comparisons than laboratory studies.
One pilot randomized study involving people with single-event PTSD compared several types of auditory and kinesthetic stimulation used within EMDR. The different forms were clinically useful, but alternating stimulation appeared to provide additional benefit in that small study. emdr.com
Other clinical work has found eye movements superior to auditory tones for reducing the vividness and emotionality of trauma memories. EMDR HAP
However, these studies are far fewer than the broader research establishing EMDR as a treatment.
That means we can be more confident saying EMDR is effective for PTSD than saying all methods of bilateral stimulation are clinically equivalent.
Those are different evidence questions.
Why Does EMDR Use Alternatives to Eye Movements?
Eye movements are not always practical or preferred.
A person may have difficulty visually tracking a moving target. A particular setting may make eye movements inconvenient. Other forms of stimulation may simply be easier to use in some circumstances.
The VA National Center for PTSD notes that EMDR can use light bars, tactile devices, self-tapping, auditory tones, and other methods in addition to therapist-guided eye movements. VAntage Point
So alternatives are part of contemporary EMDR practice.
Research simply tells us that the strength and type of evidence are not identical for every method.
Are Eye Movements “Better” Than Tapping or Tones?
The evidence supports a narrower statement.
In several experimental comparisons, eye movements have produced larger reductions in memory vividness and emotionality than simple tapping or auditory tones. Frontiers
But that does not establish that eye movements will be clinically superior in every person, every setting, or every full EMDR treatment.
Most of those comparisons examine a particular mechanism—such as memory vividness—rather than the entire treatment outcome.
It is therefore more accurate to say:
Eye movements currently have the strongest and most extensive experimental support among the commonly used bilateral-stimulation methods. Other methods can also affect memory processing, but the evidence for them is smaller and the effects are not always identical.
What Can We Reasonably Conclude?
Research has studied several forms of stimulation used alongside memory recall, but not equally.
Eye movements have received by far the most research attention. Laboratory and clinical studies repeatedly show that recalling an unpleasant memory while making eye movements can reduce its vividness and emotional intensity. PubMed Central (PMC)
Tapping has also been studied. More cognitively demanding tapping tasks can reduce vividness and emotionality, supporting the idea that working-memory competition may matter. Simple tapping has not consistently produced effects as large as eye movements. Frontiers
Auditory tones and beeps have been studied as well. They can affect memory experience, but direct comparisons have often found smaller effects than with eye movements. emdr.com
Taken together, the evidence does not support assuming that eye movements, tapping, tones, and other bilateral methods are scientifically interchangeable.
It suggests instead that different tasks can influence memory processing, probably in part because they divide attention and tax working memory to different degrees.
Frequently Asked Questions
Are eye movements necessary for EMDR to work?
Eye movements are the most extensively studied form of bilateral stimulation, but other tasks have also been shown to affect memory vividness and emotionality. The precise contribution of eye movements to the full EMDR treatment remains an active area of research. Frontiers
Has tapping been scientifically studied?
Yes. Experimental studies have examined tapping, particularly spatial or complex tapping tasks. Some have found reductions in memory vividness or emotionality, although the effects are not always as large as those produced by eye movements. Frontiers
Have alternating tones been studied?
Yes. Auditory tones and beeps have been tested in both laboratory and clinical research. Some studies find that they affect memory experience, but direct comparisons have generally found stronger reductions in vividness and emotionality with eye movements. emdr.com
Does bilateral stimulation have to alternate left and right?
Not necessarily according to the working-memory explanation. Several non-bilateral tasks that strongly tax working memory have also reduced memory vividness and emotionality in experiments. This is one reason researchers continue debating whether bilaterality itself is the critical factor. PubMed Central (PMC)
Are all forms of bilateral stimulation equally well researched?
No. Eye movements have the largest research base. Tapping, tones, and other methods have been studied less extensively, and the available evidence does not show that every form has identical effects.
Conclusion
Eye movements, tapping, and tones are all used within EMDR, but the research behind them is not identical.
Eye movements have been studied most extensively and have the clearest evidence for reducing the vividness and emotional intensity of unpleasant memories during recall.
Tapping can also place demands on working memory and influence how memories are experienced, particularly when the task requires meaningful attention.
Auditory tones have shown effects as well, although several direct comparisons have found them less powerful than eye movements for reducing memory vividness and emotionality.
These findings support a broader scientific idea: the additional task performed during memory recall may matter partly because it competes for limited mental resources.
But they do not establish that every tapping pattern, tone, eye-movement speed, or bilateral device produces the same effect.
What research has actually studied is a collection of related but different tasks—and so far, eye movements remain the most extensively tested of them.
