Our short-term memory is wired to deceive people on purpose, and a new study explains why. For instance, when people look at the same object twice, the second glance reflects a slightly different image, which are the workings of short-term memory as it makes a systematic mistake.
These mistakes help in stabilizing the continually changing impressions of the environment explains a new study published in the journal Nature Communications. A team of researchers at the Institute of Medical Psychology at Goethe University reconstructed a common scenario people experience all the time, even as children.
Short-term memory mistakes
When crossing the street, children were taught to look left and right before going forward. It is a way to see if vehicles are approaching, and it is safe to cross. The scenario fits perfectly in explaining serial dependence, which refers to the notion that returns evolve nonrandomly.
Put simply, when crossing the street, you look left and see a car and a cyclist coming, then you look right. You look left again and see the car and cyclist, only in a different position and light. It may look like a simple task, but the brain had to do some mental gymnastics to tell that what you saw are the same car and cyclist.
The short-term memory deceives people. The car and the cyclist are the same objects, but they do not have the same characteristics as before. They may have different colors due to lighting and different locations since they are moving. The brain recognizes that the vehicles seen a while ago were the same ones on second glance.
The scientists reconstructed the traffic scenario in the laboratory. The team recruited student participants and asked them to remember the movement and direction of green or red dots moving across a monitor. For each trial, the person will see two moving dot fields in short succession. Then in additional tests, both dot fields were seen at the same time next to each other.
"We test whether congruent context features, in addition to content similarity, support serial dependence. In four experiments, we observe a stronger serial dependence between objects that share the same context features across trials," the researchers explained.
The researchers focused on the mistakes made by the participants and how these mistakes were connected in successive trials. The team used the test to approximate real situations wherein people have different forms of visual information from objects. The contractual information, particularly sequence and space, help to the misrepresentation of successive perception in short-term memory.
The short-term memory uses cues from motion direction, particular position, and color to launch intentional mistakes. The contextual information aids in the differentiation among various objects and to assimilate information of the same object through time.
Going back to the crossing the road analogy, the tests in the laboratory showed that the short-term memory can process its perceptions of both the car and cyclist separately. This means that the brain processes its perception based on when they were, to begin with, not where they were in relation to each other.
"Initially, it doesn't sound good if our short-term memory reflects something different from what we physically see. But if our short-term memory were unable to do this, we would see a completely new traffic situation when we looked to the left a second time. That would be quite confusing because a different car and a different cyclist would have suddenly appeared out of nowhere. The slight 'blurring' of our perception by memory ultimately leads us to perceive our environment, whose appearance is constantly changing due to motion and light changes, as stable. In this process, the current perception of the car, for example, is only affected by the previous perception of the car, but not by the perception of the cyclist," Christoph Bledowsk, a psychologist at the Goethe University, said.
There is more about the short-term memory's tricks that scientists need to explore. The blurring of the perception by the memory helps people perceive the environment and how to navigate in it.
- Fischer, C., Czoschke, S., Peters, B., Rahm, B., Kaiser, J., and Bledowski, C. (2020).Context information supports serial dependence of multiple visual objects across memory episodes. Nature Communications. https://www.nature.com/articles/s41467-020-15874-w