Human Memory May Be Untrustworthy After Just a Few Seconds

Human memory is not always as accurate as we might think. Credit: Pedro Silva / Flickr / CC BY 2.0

Recent research has revealed that our short-term memory is not always as accurate as we might think. Even memories from just a few seconds ago can be prone to errors, according to a team of scientists who have coined the term “short-term memory illusions” to describe this phenomenon.

Dr. Marte Otten, the author of the research, at the University of Amsterdam said, “Even at the shortest term, our memory might not be fully reliable.”

She further said, “Particularly when we have strong expectations about how the world should be, when our memory starts fading a little bit – even after one and a half seconds, two seconds, three seconds – then we start filling in based on our expectations.”

Short Term Memory Illusions

To understand more about short-term memory illusions, the researchers conducted four experiments. In the first experiment, participants were asked to complete basic visual memory tasks before being shown a circle of letters, some of which were mirror images.

After a few seconds, they were shown a second circle of letters and were instructed to ignore it. They were then asked to choose a target shape from the first circle and rate their confidence in their choice.

The results showed that participants frequently chose the mirrored form of the target shape, especially when the target shape itself was a mirrored letter. This suggests that the mistakes were not due to the appearance of the shapes but rather to participants’ knowledge of the alphabet and their expectations.

In an article published in the academic journal Plos One, the researchers explain that previous studies have shown people tend to remember a rotated or mirror-image letter in its correct orientation. Until now, this was assumed to be a case of misperception on the part of the participants.

However, the team led by Dr. Otten found reason to doubt this assumption. Their study shed new light on our ability to recall shapes and highlighted the potential for our memories to become distorted over even a short period of time.

Short-Term Memory Vs. Perception Errors

As the delay period or level of distraction in the experiment increased, the number of errors also increased, but only when the target shape was a mirrored letter. This indicates that the errors were due to mistakes in short-term memory, rather than perception, as perception does not deteriorate over time.

Short-term memory vs. perception. Credit: Xuan Zheng / Wikimedia Commons / CC BY-SA 2.0

The researchers also found that participants reported their answers with high confidence, ruling out the possibility that they were simply guessing. Similar results were obtained in three additional experiments involving a total of 348 participants.

The researchers hope to investigate whether these effects occur in real-world situations and for other types of memory. For example, they noted that details of speech are quickly replaced by the general meaning of the sentence.

“The bigger effects when it comes to social expectations might be intonation, [for example] ‘oh, she said that in a really angry and upset voice,’ right? Whereas maybe the intonation wasn’t that, but it’s just colored quickly in your memory based on your assumptions about how women are,” Dr. Otten said.