Our brains are notoriously untrustworthy. They like to fill in any gaps so that they can neatly package up and file away information. From cognitive biases to inventing memories to convincing us we’re hearing things that aren't there, our brains are fascinatingly unreliable.
We know that we all have blind spots in our vision and that our brains “fill in” what it assumes is there based on surrounding visual cues. Now, a new study published in eLife has shown that we actually trust this invented visual information more than the real thing.
The researchers, from the University of Osnabrück, Germany, revealed that when it comes to choosing between two identical images, one generated by the brain “internally”, using surrounding clues to fill in a blind spot, and one generated “externally” from the real world, we are more likely to show a bias towards the internal information.
“While [the brain’s] fill-in is normally accurate enough, it is mostly unreliable because no actual information from the real world ever reaches the brain,” senior author Professor Peter König said in a statement. “We wanted to find out if we typically handle this filled-in information differently to real, direct sensory information, or whether we treat it as equal.”
To test this, they got 100 participants to look at two circles, both with vertical stripes. One circle also had a small patch with horizontal stripes. The participants were asked to identify the circle with uninterrupted stripes. When the circle with the horizontal stripes was placed in the blind spot, the brain filled in the image so that both circles appeared to have continuous stripes.
The researchers expected people to either not be aware of their blind spot and just guess or, if they were subconsciously aware of it, to choose the actual uninterrupted striped circle. Instead, the opposite happened. Sixty-five percent of the people were much quicker to choose the image placed in the blind spot that required the brain to fill in the image.
The researchers think this is because the brain compares the internal image it is creating to the external sensory information fed to it and, in finding a difference, reads it as an error. “The brain trusts its own generated information more than what it sees outside in the world,” Ehinger told New Scientist.
The researchers say there doesn't seem to be an obvious benefit for choosing internal over external information, but it does tie in with what we know about cognitive biases; when people believe something strongly, they are more likely to ignore contradictory evidence.
The team concluded that understanding how we assimilate information helps us understand how the brain makes decisions based on our perceptions.
