New Illusion Experiment Claims Brain Can Retroactively Change Perceptions Of Reality

Wednesday, 10 October 2018 - 10:46AM
Technology
Neuroscience
Wednesday, 10 October 2018 - 10:46AM
New Illusion Experiment Claims Brain Can Retroactively Change Perceptions Of Reality
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By now, most of us are familiar with the 'Invisible Gorilla' experiment, which shows how selective our attention can be, but now a research team from Caltech (The California Institute of Technology) has found that our brain can mess with our perceptions in other ways—including changing our memories to fit a non-existent reality.

The new research, published in the journal PLOS Oneis centered on two experiments that use flashes of light accompanied by beeps. The first experiment, called the "Illusory Rabbit," instructs a participant to focus on a cross in the center of a screen, then count the number of vertical bars of light they see near the bottom of the screen using their peripheral vision. The bars of light only flash for 58 milliseconds, and appear first on the left side of the screen, then the right. To make it simple, there are only two of them, and each one is paired with a short beep when they light up.

Here's the rub, though: despite there being only two bars of light, there are three beeps, including one that happens between the first and second bars lighting up.

Because the lights and sounds happen so quickly, human perception is glitched: researchers found that participants in the study tended to count three flashes instead of two, apparently reacting to the audio stimuli (the beeps) rather than the visual stimuli. Because there was no third bar of light in between the real two, researchers claim that this experiment shows how the brain "fills in the blanks" to fit patterns it observes, even retroactively changing perceptions (and memory) to fit what it believes did happen.

According to Noelle Stiles, one of the authors on the new study: "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. This already implies a postdictive mechanism at work. But even more importantly, 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."

A second, similar experiment dubbed "The Invisible Rabbit" drives this point home: participants were given a test identical to the first, only with three bars of light appearing in quick succession but only two beeps playing, one for the first and one for the third. This created the opposite result: participants reported seeing only two bars of light, apparently ignoring the visual stimuli when no aural stimuli was paired with it.



So our perceptions of reality may be more plastic than we might have guessed, as long as things happen rapidly enough to confuse our brain. Sounds like the basis for a Black Mirror episode... or the next election.
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