Your Brain May Flicker Between What You See and Don't Notice 15 Times a Second

Your brain may be quietly switching between the image you are aware of and one that never reaches your awareness, about 15 times every second. That is the suggestion of a new preprint study in macaque monkeys and humans, reported by ScienceAlert. The work has not yet been peer-reviewed, and it rests on a very small number of animals.

The research was led by neuroscientists Janis Hesse and Doris Tsao of the University of California, Berkeley. It targets a basic puzzle: at any moment, only part of the brain's activity becomes conscious experience, while the rest is processed without being felt. The team described how that split arises as one of the most basic unsolved problems in neuroscience.

Why researchers looked at time instead of place

For decades, scientists have searched for the brain regions that become active when a person consciously perceives something. A problem emerged along the way: the same regions can also respond to stimuli that people never notice. Hesse and colleagues asked whether the search had focused on the wrong dimension. Instead of asking where in the brain the difference lies, they asked whether it shows up in how activity changes over time.

How the experiment worked

The team used a classic trick called binocular flash suppression. The macaques wore anaglyph glasses, the kind with one red and one cyan lens, so that each eye saw a different image. One face was shown to one eye. While it stayed in place, a second face was suddenly shown to the other eye.

Rather than seeing both faces, the brain tends to favor the newly introduced one and push the first out of awareness. The first face is still reaching the eye, but it is no longer consciously perceived. Because the monkeys could not report what they saw, humans were recruited to confirm that the second face dominates conscious perception with this method.

The researchers then recorded electrical activity from hundreds of neurons at once, using tiny electrodes placed in visual areas, including regions that specialize in recognizing faces. They found one pattern of activity linked to the first face and another linked to the second.

What they found

Although the second face was expected to dominate, the neurons did not hold steadily to it. Their activity alternated rapidly between the face that was consciously perceived and the one suppressed from awareness, roughly 15 times a second. In the moments when a face was consciously perceived, neurons also responded more sharply to its features than they did to the suppressed face during the suppressed moments. That hints that the brain has a way to tell the two states apart even as it switches between them.

The study does not explain how the brain decides which information reaches consciousness. The authors speculate that the rapid switching may let the brain weigh alternative interpretations of a scene without changing what a person is currently doing.

What this means for how we think about experience

The result suggests that the smooth, steady view of the world you experience may be built on fast and complex activity that you never notice. It also raises the possibility that something other than what is visually available helps shape what you consciously see.

The limits are important. Only two macaques took part, and their conscious perception had to be inferred from the human experiments. The researchers also looked only at specific visual regions, not the whole brain. Until the findings are reviewed and repeated, they are best read as an intriguing early signal rather than a settled description of how awareness works.

Around Prague, based on reporting by ScienceAlert