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it Is a mystery whose resolution leads to escape of scientific knowledge for a century: why have two forms with identical colors are perceived in a different tone if put in a gradient background? Now, a new study from MIT published in the journal “Vision Research” comes to unravel the mystery.

Our perception of the tones and the colors changes according to its visual context, a process known as simultaneous contrast of brightness . If a shape is surrounded by something dark, we perceive it as brighter than if he were in lighter shades. This effect has been explored by scientists since at least the NINETEENTH century, as well as artists. But there are still unanswered questions: Where exactly is the bug that creates these “lies” visuals? Do we deceive our eyes? Or is it the brain?

Some experts believe that this visual trick happens due to the visual processing high-level : our brain provide us with an interpretation of what our eyes are sensing, after taking into account the lighting and environmental conditions .

But this new research suggests opposite . The researchers subjected to 27 volunteers to a series of visual tests specific, including the presentation of the images subtly different for each one. To test whether our interpretation of what we are seeing is due to shadows or perceived due to the actual level of light emitted ( luminance ), the team taught their subjects an illusion like the one shown below.

Sinha et al., Vision Research, 2020

“we Created a version where the side that was actually of higher luminance was perceived as darker and vice versa”, described by the researchers in their article. “This is the opposite of what happens on the screens of contrast, simultaneous standard, in which a point on a dark background looks brighter than a point on a light background,” explains the neuroscientist computational Pawan Sinha of MIT.

The luminance, of which we are not always aware of, contributes to our estimates of brightness, which suggests that you do not require processes of high-level thinking to make this judgment between the contrasts . On the contrary, the study suggests that our estimates of the brightness occur very quickly in our route of visual processing , even before the information from both eyes is merged in our brains.

“Our experiments point to the conclusion that this is a phenomenon of low-level ,” says Sinha. “This is a innate ability of our visual system from birth “.

Sinha et al., Vision Research, 2020Segundo experiment

To test this end, we conducted a second experiment. is Nine children between 8 and 17 years old with congenital blindness newly operated cataract also saw this illusion. In theory, if the estimation of the brightness is, in effect, an innate mechanism, these children after seeing for the first time with their eyes should fall on the same optical illusion: to perceive the ways of a different color despite being of the same tone.

And that is what happened. Only 24-48 hours after it is removed the surgical dressings, the children fell into the illusion , which shows that this perception is not learn it with the time and is influenced by the past experiences .

Sinha pointed out that their findings are consistent with others that arise from the studies of brightness, but there are some aspects that the team still can not explain. This can mean that other processes in the brain are also involved in later stages, even though they are convinced that the estimates of contrast involve an innate mechanism in the early visual system.