However, this is actually the result of the brain playing a trick on the participant.
Photo / Caltech
Scientists refer to the illusion as the 'Illusory Rabbit.'
"Though only two flashes are played, most people viewing the illusion perceive three flashes, with an illusory flash coinciding with the second beep and appearing to be located in the center of the screen," Caltech explained.
This illusion can be explained by a phenomenon in the brain called "postdictive processing".
"When the final beep-flash pair is later presented, the brain assumes that it must have missed the flash associated with the unpaired beep and quite literally makes up the fact that there must have been a second flash that it missed," Noelle Stiles, lead author of the study, told Caltech.
"This already implies a postdictive mechanism at work.
"But even more importantly, the only way that you could perceive the 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."
Illusions can sometimes elicit postdiction, where our brains gather information after an event has occurred, in order to retroactively explain what may have happened at the time of an event.
For this study, it explains how postdiction often centers around the ways in which our brains interpret different senses, as well as how our senses influence one another.
"Illusions are a really interesting window into the brain," Stiles said.
"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," Stiles explained.
Scientists say it can help explain how our brain combines the senses over space and time to develop an explanation of what occurred.
"Postdiction may sound mysterious, but it is not—one must consider how long it takes the brain to process earlier visual stimuli, during which time subsequent stimuli from a different sense can affect or modulate the first," Shinsuke Shimojo, a researcher in the study, explained.
"...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."
How to do the illusion
Focus on the cross in the middle of the screen.
Listen to the beeps and pay attention to the number of flashes on the bottom of the screen.
