An illusion that warps our perception of time – altering our recollection of events to make it seem as if they occurred further into the past – may force a rethink of our existing theories of memory.
Our ability to recall past events requires information on what happened as well as when and where, but because , our recollection of when they were formed is fallible. For example, have found that seeing a name multiple times can lead people to believe they had encountered it more recently than was truly the case.
One way to explain this is that repeated experiences of the previous occasion, potentially strengthening the original memory. Intuitively, a stronger memory might be expected to be more recent, as our memories of events can fade over time. But at the University of Pennsylvania says these findings didn’t tally with her and her colleagues’ personal experiences of memory.
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To investigate further, the team ran a series of experiments to see how repeatedly seeing an image affected people’s perception of when they had first seen it. Although these experiments varied, participants were generally shown five blocks of 50 images, with some of the images shown just once across all the blocks and some repeated two, three or five times. They were then asked to place when they had seen each image along a timeline.
The researchers found that not only did participants have a better memory of images they had seen more than once, in line with the idea that repeated experiences can strengthen a memory, they also remembered the repeated images as having first appeared earlier than they actually did. The size of this “temporal repetition effect” also scaled with the number of repetitions: images repeated five times were remembered as having been encountered further back than items repeated three times, and so on.
Participants may have tried to figure out when they had first seen an image by using certain strategies, like presuming that something must have first occurred longer ago if it could be repeated, says Sherman. But when she asked participants if they had used any rules of thumb, these rules didn’t actually match the way they had ordered the images. “So we do think it might be some genuine memory effect, not just a heuristic,” she says.
To test whether the illusion remained over a longer time period, the researchers ran one experiment over a week, with the participants seeing a block of 100 images each day from Monday to Friday and then completing the memory test on the following Monday. Crucially, the participants still experienced the temporal repetition effect.
“The fact that our effect diverges from the previous literature maybe suggests that there are different mechanisms at play for remembering when something first occurred versus remembering when something most recently occurred,” says Sherman.
at Durham University, UK, says the finding is hard to reconcile with our current understanding of memory. It doesn’t match our idea that the strength of a memory affects how recently it is believed to have occurred, he says, or that other stimuli can help to place a memory in time, such as associating an event with the particular mood you were in. “Instead, what it’s suggesting is that there is some other thing going on, which is feeding into our memories to help us get an idea of when something happened,” he says.
at George Mason University in Virginia says the results could, however, be explained by the way our brains experience time. For example, suggest that the brain treats lengths of time in the same way it treats physical size, with showing that people can remember large objects, like a sports stadium, better than smaller ones. “It’s possible that by having the repeated events like this over and over again, the magnitude of time for that event has grown,” says Wiener, making it feel longer ago.
“What we really need now is a chance to try and rethink the science of memory,” says Easton, so we can find a way to understand both the new and existing results in the same framework.
PsyArXiv
