As children, many of us encountered optical illusions, such as Rubin’s Vase, which could be perceived as either two faces or a vase. Using this concept, a new study published in the journal Psychological Science demonstrates that our brains process visual input that we may never perceive consciously.

The study, led by doctoral degree candidate Jay Sanguinetti at the University of Arizona (UA), challenges widely accepted ideas about how the brain processes visual data.

While showing participants various images of black silhouettes – some that contained hidden objects in the bordering white spaces and some that did not – Sanguinetti and his team monitored their brainwaves with an electroencephalogram (EEG).

The brainwaves suggested that even when the subjects did not consciously recognize the bordering shapes, their brains had analyzed those shapes and grasped their meaning.

2 white seahorses looking at each other or a black candlestickShare on Pinterest
Study participants looked at images of black silhouettes. Sometimes, there were real-world objects hidden at the borders of the black silhouette, like the two seahorses in the white spaces shown here.
Image credit: Jay Sanguinetti

“We were asking the question of whether the brain was processing the meaning of the objects that are on the outside of these silhouettes,” says Sanguinetti.

“The specific question was, ‘Does the brain process those hidden shapes to the level of meaning, even when the subject doesn’t consciously see them?'”

They found that the answer is yes, after focusing on a “brain signature for meaningful processing.”

According to Sanguinetti, a peak in the averaged brainwaves signifies that the brain has identified an object and linked it with a certain meaning. In terms of this study, a peak shows that the brain recognizes the meaning of the shapes on the outside of the figure.

Though the images were only shown to study participants for 170 milliseconds, their brains were able to perform complex processes in order to interpret the meaning of the hidden objects.

The team used some images with novel shapes in the middle and nothing meaningful on the outside, which served as controls.

Mary Peterson, professor of psychology and director of UA’s Cognitive Science Program, also worked with Sanguinetti and says:

The participants in our experiments don’t see those shapes on the outside; nonetheless, the brain signature tells us that they have processed the meaning of those shapes. But the brain rejects them as interpretations, and if it rejects the shapes from conscious perception, then you won’t have any awareness of them.”

Sanguinetti notes that their findings prompt the question of why the brain processes the meaning of certain shapes when we ultimately are not going to perceive them.

“The traditional opinion in vision research is that this would be wasteful in terms of resources,” he says. “If you’re not going to ultimately see the object on the outside, why whould the brain waste all these processing resources and process that image up to the level of meaning?”

Peterson suggests that our brains may have evolved to sort through the wide range of visual data that our eyes take in and pick which things are most important for us to be aware of – such as threats or resources.

Now that they have established these recent findings, Peterson and Sanguinetti would like to explore the specific regions in the brain where this processing of meaning happens.

“The EEG tells us this processing is happening and it tells us when it’s happening,” says Peterson, “but it doesn’t tell us where it’s occurring in the brain.”

Sanguinetti adds that the brain works to give us the best and most useful interpretation of the world around us, but this interpretation does not include all the visual information that our brain receives.

They conclude their study by writing that their experiments “provide the first neurophysiological evidence that semantic access can occur for the apparently shapeless ground side of a border.”