How this illusion of time travel deceives your brain

Do you want to travel in time, if only for a moment?

Although science has not yet overcome this obstacle (except perhaps for light particles), people can at least feel as in a journey back in time looking at two newly created illusions.

These illusions, which involve flashing lights and deafening ringtones, show that a new stimulus can change the perception that people have a stimulus that occurred a fraction of a second ago , according to a new study published online Oct. 3 in the journal PLOS ONE.

This phenomenon is called postdiction. Unlike prediction, when you are trying to predict the future, postdiction occurs when a future stimulus influences your view of the past. [The Most Amazing Optical Illusions (and How They Work)]

"Illusions are a really interesting window on the brain," said Noelle Stiles, the first author of the study, a researcher in biology and bioengineering at the California Institute of Technology and a postdoctoral research associate at the California Institute of Technology. University of Southern California. declaration. "By investigating illusions, we can study the decision-making process of the brain."

When implementing the illusion, researchers realized that to trap the brain, stimuli should occur almost simultaneously, less than 200 milliseconds (one-fifth of a second). They discovered that the brain was trying to understand a barrage of flashes and buzzers by synthesizing the different senses (visual and sound) with the help of the postdiction.

In the first illusion – called the illusory rabbit – the researchers made a video in three parts: (1) a beep and a flash on the left side of the screen, followed by (2) a beep, then (3) ) followed by another beep and flash on the right side of the screen. Only 58 milliseconds separate each part of the video.

However, even though there are only two lightning bolts, most people have seen three. There is no flash at the second beep, but people tend to report seeing a flash in the middle of the screen when the second beep sounds. You can see it yourself in the video below.

Since the illusory flash is perceived between the left and right flashes, it seems that the brain uses a postdiction treatment to fill the void, said the researchers.

"When the final beep-flash torque is presented, the brain assumes that it had to miss the flash associated with the unpaired beep and literally explains the fact that there must have been a second flash that's going on." he missed, "said Stiles. "It already involves a post-work mechanism at work. But more importantly, the only way to perceive the illusory flash moved would be that the information provided later (the final beep-flash combination) be used to reconstruct the most likely. location from the illusory flash too. "

The second illusion is nicknamed the invisible rabbit. In this illusion, three lights flash on one screen – the first on the left, the second on the center and finally the right, with beeps at the first and third blinks. However, most people do not see the second flash, simply because it does not ring.

It's actually a big problem for scientists. By showing that sound can lead to a visual illusion, the research team has shown how the brain combines the senses in space and time to generate an integrated sense of perception.

"The importance of this study is twofold," said lead author Shinsuke Shimojo, a professor of experimental psychology at Caltech. "First, he generalizes postdiction as a key process of perceptual treatment for a single sense and for multiple meanings," said Shimojo, referring to sight in the first experience and sight and sound in the second.

"The postdiction may seem mysterious, but it is not. Consider the amount of time it takes the brain to process previous visual stimuli, during which later stimuli from a different direction can affect or modulate the former. "

The experiments on rabbits also reveal that "these illusions are among the very rare cases where sound affects vision, not vice versa, indicating the dynamic aspects of neuronal processing that occur in space and time, "said Shimojo.