Most people intuitively understand that a memory fades over time. But why do some parts remain while others disappear? A new study published today in Nature Communications by a team of researchers from the Universities of Glasgow and Birmingham provides some answers.
They found that over time our memories become less vivid and detailed, and only the essentials remains, which is perhaps a bit obvious. What is less obvious, however, is the finding that the more frequently we recall our recent experiences, the greater the effect of this process of “gistification”. In other words, every time we think about it, we contribute to the loss of detail in our own memories.
All memories fade eventually, but some sooner than others
While memories are always exact carbons of the past, experts have long suggested that the contents of a memory change each time we bring them back to mind.
But how exactly our memories differ from original experiences and how they change over time has so far proven difficult to measure in laboratory settings.
For this study, the researchers developed a simple computer-based task that measures how quickly people can recover certain features of visual memories when prompted.
The study consisted of 72 participants, mostly recruited from local universities, with an average age of 20 years. Participants learned word-image pairs and later had to remember different elements of the image when called out with the word. For example, participants were asked to indicate as quickly as possible whether the image was color or black and white (a perceptual detail), or whether it showed an animate or inanimate object (a semantic element).
These tests took place immediately after learning and also with a two-day delay. Reaction time patterns showed that participants recalled meaningful, semantic elements faster than superficial, perceptual ones.
Our natural preference for the essentials: we focus on the meaningful part of a story
Many theories of memory assume that over time, when people retell their stories, they tend to forget the superficial details but retain the meaningful, semantic content of an event, said lead author Julia Lifanov from the University of Birmingham.
Imagine remembering a dinner with a friend, she said. “You realize you can’t remember the table setting but know exactly what you ordered; or you remember the conversation you had with the bartender but not the color of his shirt.” Memory researchers call this phenomenon “semantization”.
This tendency to remember meaningful, semantic items that the researchers Demonstrate in this study suggests that memories are a priori biased toward meaningful content, said co-author Maria Wimber of the University of Glasgow. “We have shown in previous studies that this distortion is also reflected clearly in brain signals,” she said.
And there are good reasons for this selectivity. “Our memories change with time and use, and that’s a good and adaptive thing,” Wimber said. “We want our memories to retain the information that is most likely to be useful in the future when we encounter similar situations.”
A memory fades more and faster when remembered repeatedly
Interestingly, the researchers found that this propensity for semantic (i.e., meaningful) memories increases significantly over time and with repeated recall.
For example, when the participants returned to the lab two days later, they were much slower in answering the detailed, “perceptual” questions, but they showed well-preserved memories of the semantic content of the images.
This effect was much weaker in participants who viewed the original image multiple times, rather than having to laboriously recall it multiple times.
This work could impact a number of have areas, e.g. such as post-traumatic stress disorder, in which patients often suffer from intrusive, traumatic memories and tend to generalize these experiences to new situations
The results are also very relevant to understanding how eyewitness memories are biased can, for example, through frequent interviews and repeated reminders of the same event.
And last but not least, these results also show that the meaningful information sticks longer through self-tests before an exam (e.g. with index cards), especially when p follows periods of rest and sleep.
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Study: “Feature- specific reaction times reveal a semanticization of memories over time and with repeated recall”Authors: Julia Lifanov, Juan Linde-Domingo and Maria WimberPublished in: Nature Communications Publication Date: May 26, 2021DOI: https://doi.org/10.1038/s41467-021-23288-5Photo: by Lisa from Pexels