Time Travel Illusions Created by Scientists Trick the Brain into Seeing Things That Aren't There

Scientists have created two time travel illusions that show how the brain processes information to make sense of conflicting stimuli.

The two illusions, called the Illusory Rabbit and the Invisible Rabbit, focus on audio and visual cues, revealing how a stimulus that occurs at a later point can affect the perception of stimuli that have already occured—effectively making your brain time travel.

The phenomenon is known as postdictive processing. This is the opposite of prediction—where the brain expects certain things to happen based on specific cues. Instead, the brain retroactively alters our perception of an earlier event based on stimuli that happen later.

Previously, scientists have shown postdictive processing within individual senses. However, in two new illusions, researchers led by Shinsuke Shimojo, from Caltech, show it happening across both our audio and visual senses, indicating the interplay between the two. Their findings are published in the journal PLOS One.

"Illusions are a really interesting window into the brain," study first author Noelle Stiles, from the University of Southern California, said in a statement. "By investigating illusions, we can study the brain's decision-making process. For example, how does the brain determine reality with information from multiple senses that is at times noisy and conflicting? The brain uses assumptions about the environment to solve this problem. When these assumptions happen to be wrong, illusions can occur as the brain tries to make the best sense of a confusing situation. We can use these illusions to unveil the underlying inferences that the brain makes."

In the first illusion, a cross appears on the screen. This is followed by two flashes of light accompanied by three beeps. When the middle beep plays there is no flash. However, because there is a flash with the third beep, our brains retrospectively fill in the gap and we see a third flash.

The brain assumes that it must have missed the flash associated with the unpaired beep and makes up the fact that there must have been a second flash that it missed. "The only way that you could perceive the shifted illusory flash would be if the information that comes later in time—the final beep-flash combination—is being used to reconstruct the most likely location of the illusory flash as well," said Stiles.

In the second illusion, three flashes are shown and two beeps—the beeps play during the first and third flash. Findings show most people do not see the second flash. Our brains cut it out because there is no audio cue to go alongside it.

Shimojo said the study is significant because it shows perceptual processing over multiple senses. "These illusions are among the very rare cases where sound affects vision, not vice versa, indicating dynamic aspects of neural processing that occur across space and time," he said. "These new illusions will enable researchers to identify optimal parameters for multisensory integration, which is necessary for both the design of ideal sensory aids and optimal training for low-vision individuals."

Shimojo told Newsweek the findings suggest our memories are constantly being altered through postdictive processing—evidence of this is found in his own laboratory work and through social science research. Potentially, the findings could be used to develop treatments for disorders like post traumatic stress disorder (PTSD): "It may be partly already tried," Shimojo said, "and should be extended much more."

Next, the team plans to extend the list of postdictive multisensory integration to other illusions. "In the long-term, we do need to understand predictive-postidictive interactions in the brain across implicit and explicit levels of mind."

This story has been updated to include quotes from Shinsuke Shimojo.