Scientists have created an optical illusion that drives your brain on a journey back in time

How does the brain give meaning to all the information we bomb every second of every day?

It's a complicated question, but researchers have invented two new illusions that give us clues: an optical and an auditory. And they both cheat the brain to bring it back in time to fill in the gaps that it thinks to miss.

This is technically called postdiction, where a stimulus can affect what we think we have seen or heard in the past – as opposed to the prediction, which works in the past. other meaning, continues in time.

The two illusions, the illusory rabbit and the invisible rabbit, are among the first to show that the postdiction operates in several senses: sound and vision. They help to demonstrate that something we think happened may not have happened at all.

"How does the brain determine reality with information from multiple senses that are sometimes noisy and conflicting? The brain uses environmental assumptions to solve this problem," says one of the researchers, Noelle Stiles from the California Institute of Technology (Caltech). ""

"When these assumptions turn out to be false, illusions can occur when the brain tries to give the best possible meaning to a confusing situation.We can use these illusions to reveal the underlying inferences made by the brain."

You can view the illusionary rabbit by yourself below. How many flashes do you see?

Here's how illusions work: imagine a beep and a flash on the screen appear almost simultaneously.

Now imagine three of these combinations, just 58 milliseconds apart, when blinking moves from left to right on a screen (the beep sounds in the center).

In the illusory rabbit, the average flash never occurs, but most people still think they have seen three flashes corresponding to three beeps.

In Invisible Rabbit, it's the middle beep that is missing – and the brain generally thinks that there was no flash medium.

The fact that the middle beep or flash is manipulated shows postdiction at work – it's actually the last flash and beep that causes the illusion. They make our brain change what it perceived in the past.

"The interest of this study is twofold," said lead researcher Shinsuke Shimojo of Caltech. "First, it generalizes postdiction as a key process of perceptual processing for a single sense and for many senses."

"The second meaning is that these illusions are among the very rare cases where sound affects vision, not the opposite, indicating the dynamic aspects of neuronal processing that occur in space and time. "

All of this should be useful as scientists try to understand how the brain makes sense of the world and presents us with the information. We still have a long way to go to understand the inner workings of the brain and how the perception of the mind works.

Of course, we make fairly important decisions based on what we think are happening – so it's important to do it right. Many mental illnesses also cause perception problems. The more we know, the better we can find solutions.

"Illusions are a really interesting window on the brain," says Stiles. "By investigating illusions, we can study the decision-making process of the brain."

The search was published in PLOS One.

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