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Is It Possible To Forget? Investigating the Suppression of Memories

The views expressed are those of the author and are not necessarily those of Scientific American.


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Everyone has experiences happen to them that they’d rather forget about. Every so often though, you might have a reminder of that experience: perhaps someone says something to you or you see something that jogs your memory. When this happens, and that memory rises to the surface, you may try to block that memory, or distract yourself with something else. However, while for most people, reminders of a bad experience generally lessen over time, for others they don’t. Such intrusive memories that continue for a long period of time are considered to be a sign that the person may develop PTSD.

It’s not just how bad the experience was that affects how much it intrudes on us in later life. Some people are able to move on from very bad experiences without constant reminders, whereas others have an experience that might not seem as bad, but they are constantly plagued by it. Even if two people had the same bad experience, one might be able to control intrusive memories while the other cannot. Why might it be that people differ in this ability?

A recent study looked into this, using a paradigm called the ‘think/ no-think’ task. In this task, people are asked to repeatedly retrieve a memory (‘think’), or to stop thinking about a memory (‘no think’), when a researcher gives them a cue that would remind them of these memories.

In this particular experiment, what this meant was that people were first asked to look at photos of traumatic scenes (combat exposure, physical and sexual assault, injuries and death, natural disasters, and serious accidents). Of course looking at a photo of a traumatic scene isn’t the same as experiencing the trauma yourself, but as scientists generally do not wish to inflict trauma upon people, this is one way to experimentally address memory formation relating to trauma.

Next to each of these traumatic photos was a picture of a neutral object. While the object was visually placed next to the scene, the object itself was in no way related to the scene, so that the person wouldn’t be able to guess what the scene was by looking at the object alone, or vice versa. Sixty of these scene-object pairs in total were shown to each person on a computer screen, one scene-object combination at a time. At first the person was just asked to look at a screen that had a single scene-object image on it. The next screen then showed just the object from the scene-object combination, and the person was asked to choose the associated scene from three options available. They did this for all sixty scene-object pairs, until they were 60% or better at recognising the scene associated with the object. The person then went on to the main part of the experiment.

An example of a scene-object combination used in the experiment. In this example, the neutral object (the basket) is placed next to the photo of the traumatic scene (a man and child dead or injured)

This time the person was shown just the object (for example, a basket), without the traumatic photo of the scene associated with it. The person was then asked to do one of two things. They either were asked to do their best to recall the traumatic scene associated with that object (for example, the image of the dead/ injured people). Or, they were asked to suppress their memory of the scene, specifically by thinking about the cue (the basket) while blocking out all thoughts of the associated scene.

The final part of the experiment tested how good peoples’ memories’ were for the traumatic photos, when they had either suppressed them or done their best to recall them. To test this, the subjects were given a test where they were shown the objects and asked to recall the scene that went with it (this time without any photos of the traumatic scenes being shown to them that might jog their memory). The researchers found that overall, people were good at remembering the traumatic scenes when they were shown the object, showing that these images had had a powerful effect on them. However, it was more difficult for people to remember the scenes that they had previously actively tried to block the memories of than the ones that they had previously been recalling as much as possible. They also remembered fewer details from the scenes that they had previously been trying to block out.

The researchers then wanted to see whether people might vary in their ability to suppress memories. To do this, they asked the subjects to fill out a questionnaire, the ‘Thought Control Ability Questionnaire’ and split the people into two groups: those that were self-reportedly good at mentally controlling their memories and those who were not. The high-control people were indeed much better at forgetting the traumatic scenes than the low-control people.

These findings may have implications for how people are treated for PTSD. By helping people gain control over their memories (specifically by inhibiting them), it could mean that they forget more of the details, reducing stress and anxiety. Of course, in some cases it is important for people to remember their trauma, but if the person wishes to forget then it’s useful to have the tools there to help them. For example, people who are exposed to traumatic experiences on a daily basis (like people who work in the emergency room of hospitals) may wish to learn how to better mentally control unwanted memories of such experiences to stop it affecting their personal lives.

 

Photo Credits

Image of object-scene combination taken from Küpper et al. 2014

 

Reference

Küpper, C. S., Benoit, R. G., Dalgleish, T., & Anderson, M. C. (2014). Direct Suppression as a Mechanism for Controlling Unpleasant Memories in Daily Life. Journal of Experimental Psychology: General. http://dx.doi.org/10.1037/a0036518

Felicity Muth About the Author: Felicity Muth is an early-career researcher with a PhD in animal cognition. Follow on Twitter @notbadscience.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. jayb61 3:16 am 05/9/2014

    They should do a study on why Politicians & Banker CEO’s suddenly lose their memories when they front a Judicial Inquiry. Now that’d be interesting.

    Link to this
  2. 2. DavisLaundon 10:25 am 05/9/2014

    I’ve already repressed the top photo from my memory, I wouldn’t be surprised if the little girl did too.

    Link to this

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