A watched pot never boils, but time flies when you’re having fun. These all-too-familiar sayings have a basis in solid science—our sense of time really does expand and contract depending on the way we experience the world around us. This is not just a general impression of time’s passage. These temporal fluctuations have a great deal to do with the intricacies of perceptual psychology. Even subtle visual features can affect how we perceive time: looking at red objects makes time pass slower than staring at blue ones. The slowdown also occurs when inspecting bigger and brighter objects and more emotional faces.
“There are a lot of illusions of time,” says Martin Wiener, a cognitive neuroscientist at George Mason University, though scientists aren’t sure what is happening in the brain to cause them. Among the illusions that are already out there, Wiener and his colleagues have found a new one that stands out because of its inherent circularity. It turns out that more memorable images seem to last longer, and these persistent images also appear to be more memorable. These findings, published in Nature Human Behavior on April 22, help reveal how the brain’s time-warping strategy might allow it to process and remember more information.
Unlike our body’s circadian rhythm, which marks time thanks to a specific group of cells in the center of the brain, our conscious, subjective sense of time does not arise from one brain region. “There’s no one single area that we’ve found that controls your sense of time; it seems like it’s a whole constellation of areas,” Wiener says. But while scientists don’t know what is actually happening in the brain when time seems to dilate, they do have an idea about why the phenomenon occurs. They suspect it may have to do with helping the brain process more information in a limited time.
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This is especially relevant for the brain’s visual system, which is subjected to a near-constant onslaught of information. With limited resources, the visual areas have to set priorities. Recent research has shown that some visual features and scenes (people’s faces or enclosed spaces, for instance) are more intrinsically memorable than others, even across different people and cultures.
“We’re surprisingly similar in what we remember and forget, even though we’re all unique people,” says Wilma Bainbridge, a cognitive neuroscientist at the University of Chicago, who has studied memorability and time perception and was not involved in the new study. “So that means that images have this innate memorability,” which scientists can now quantify using machine learning, “and that’s been shown to interact with all these interesting cognitive processes.”
Wiener and his colleagues were hoping to understand how the innate memorability of an image, along with a few simpler visual features such as scene size and clutter, might relate to our subjective sense of time. The team conducted four experiments, each with between 21 and 52 participants, in which people were shown images with time intervals that varied between 300 milliseconds and one second. In some experiments, after participants saw each image, they were asked to categorize whether the length of time on the screen was either “short” or “long.” In the final experiment, participants were asked to hold down a button to indicate the length of time the image was displayed on the screen. The next day they were given a surprise memory test to see which of the images they recalled seeing.
The researchers found that larger scene sizes seemed to dilate time and that more cluttered scenes seemed to contract it. But it was the memorability results that really stood out. Participants in the study perceived that more memorable images remained on the screen longer. And this perception also held true the other way around: for images with the same degree of memorability, participants were more likely to later recall the ones that they perceived to have lasted longer.
“The longer a person thought it had been [when they looked at the image] the previous day,” the more likely they were to remember it, Wiener says—“even though the images were all presented for the same amount of time.”
These results suggest that images aren’t just more memorable if people look at them for a longer time, a well-established effect. Images are also more memorable if people perceive that they have looked for longer when they really haven’t. This suggests that there is some underlying factor that is causing both of these effects that has yet to be uncovered, the researchers say. To predict what this factor could be, the team fed the same memorability-ranked images to a neural network modeled after the brain’s visual system and found that more memorable images were processed faster. “In other words..., memorable images may be memorable because they’re just easy for our systems to process them,” Wiener says.
Why faster processing would make time last longer is still a mystery, however. To figure this out, future studies might involve brain scans or even direct stimulation of neural tissue. For now, the most intuitive explanation for why our brain slows time is that it is increasing the amount of information it can take in at once. Here, limited resources to process information may act as a sort of bottleneck. But “it’s possible that the brain can widen the bottleneck when it needs to open things a little bit wider to take in more information. And as a consequence of this, it dilates time,” Wiener says.
This stretching of time can be minor, such as when one sees a particularly memorable image. Yet it can also be extreme, such as when one experiences a life-or-death situation in which time seems to stand still, Bainbridge says. “Sometimes something just needs that extra processing—or less processing—that changes the pace and can change how time feels,” she says.