Most of us realize that memory is fallible. We forget things all the time–car keys, passwords, whether we turned off the oven, etc. But how many of us would admit that our memory is susceptible to change from the outside? That’s different from simply forgetting–something everyone does on their own–because someone else changing our memory requires “getting in our heads” so to speak, right?
If you’ve read this blog for any length of time, you know I’m about to tell you that not only is it possible, it’s probable. And it doesn’t even take very much effort to accomplish–just a few images and a little time.
A recent study in the journal Applied Cognitive Psychology tested whether showing people photos of completed actions–such as a broken pencil or an opened envelope–could influence them to believe they’d done something they had not, particularly if they were shown the photos multiple times.
Participants were presented with a series of objects on a table, and for each object were asked to either perform an action or imagine performing an action (i.e. “crack the walnut”). One week later, the same participants were brought back and randomly presented with a series of photos on a computer screen, each of a completed action (i.e. a cracked walnut), either one, two or three times. Other participants were not shown any photos.
One week later, they were brought back to complete a memory test in which they were presented with action phrases (i.e. “I cracked a walnut”) and asked to answer whether they had performed the action, imagined performing it, or neither, and rate their confidence level for each answer on a scale of one to four.
The results: the more times people were exposed to a photo of a completed action, the more often they thought they’d completed the action, even though they had really only imagined doing it. Those shown a photo of a completed action once were twice as likely to erroneously think they’d completed the action than those not shown a photo at all. People shown a photo three times were almost three times as likely as those not shown a photo.
Two factors in this study speak to the malleability of memory. The first is duration of time. The experiment was carried out with a week between each session, enough time for the specific objects and actions to become a little cloudy in memory, but not enough time to be forgotten. This lines up well with real-world situations, such as someone providing eye-witness testimony, in which several days if not weeks might elapse between recollections of events.
The second factor is repeat exposure to images. The study showed that even just one exposure to a photo of a completed action strongly influenced incorrect memory. Multiple exposures significantly increased the errors. One real-world takeaway from this result is potentially alarming: the possibility of using images to alter someone’s memory of a face or other critical element such that his/her testimony is tainted.
A similar study discussed here tackled the same sort of memory issues with video instead of photos, and found a similar result. Both studies point to a realization becoming clearer with time: memory is far more changeable than most of us realize.
Henkel, L. (2009). Photograph-induced memory errors: When photographs make people claim they have done things they have not Applied Cognitive Psychology DOI: 10.1002/acp.1644