Even as you fix your gaze on screen in front of you to read these words, your brain may be flickering between what you consciously taking in and other visual information that never quite reaches your awareness. New preprint study involving both macaque monkeys and humans suggests brain may be switching back and forth between conscious and unconscious information around 15 times second, raising strange possibility that something other than visual availability guiding your conscious experience.
At any moment, only some of brain activity reaches conscious awareness, while rest is processed without ever being experienced, writes team led by neuroscientists Janis Hesse and Doris Tsao of University of California, Berkeley. How this division arises is among most basic unsolved problems in neuroscience, highlighting fundamental question about conscious perception and unconscious processing mechanisms and filtering.
Nose Always In Field Of View But Tuned Out
There are many things our bodies just do automatically, and sensing is one of them, we move through world under constant barrage of sensory information, and cannot turn off ability to take it in. What our brains can do is deprioritize some of that information, famous example is your nose, it always sitting bang in middle of your field of view, but your brain mostly tunes it out. You know it there; you do not need your eyes to keep confirming it, this is obviously extremely useful, without it, we would be overwhelmed by sheer volume of sensory input our brains receive.
But it also raises huge question: How does brain determine which information we consciously experience, and which information remains hidden from awareness, guiding conscious experience effectively? To seek answers, neuroscientists have spent decades studying which parts of brain become active when stimuli are being consciously perceived, over time, however, problem emerged. Same parts of brain can respond to unconscious stimuli, too, Hesse and colleagues asked new question, what if those searches were focused on wrong dimension, what if answer lay not in space, but time?
In other words, they thought way brain activity changed over time might yield clues about how brain handles conscious and unconscious visual information, shifting focus to temporal dynamics.
Red And Cyan Lenses Trick Eyes Into Seeing Different Images
Their research focused on macaques wearing anaglyph glasses, you probably familiar with glasses that have one red lens and one cyan lens, used to trick your eyes into thinking you are seeing 3D image. Same system can be exploited to show your eyes two different images, eye looking through cyan lens can see red image but not cyan one, and eye looking through red lens can see cyan image but not red one. Researchers used this trick to show macaques two different faces, first, they presented one face to one eye, then, while that image remained in place, they suddenly introduced second face to other eye.
Here is where things get weird, rather than seeing both faces at once, brain tends to prioritize newly introduced face, suppressing first from conscious awareness remarkably.
First face has not gone anywhere, eye still receiving it, but brain no longer bringing it into conscious perception, phenomenon called binocular flash suppression, very useful tool neuroscientists studying conscious and unconscious visual processing have been using for decades. Now, macaques could not tell researchers which of two images they were consciously perceiving, so humans were recruited to test technique and confirm that it was second image that dominated conscious perception. Once researchers had confirmed technique worked as expected, they turned attention to macaques brains, using tiny electrodes inserted into regions involved in visual processing, they recorded electrical activity of hundreds of neurons simultaneously as monkeys watched competing images.
Switching Occurred Around 15 Times Every Second
They were particularly interested in regions that specialize in recognizing faces, here, they identified two distinct patterns of brain activity: one linked to first face and other to second face. Interestingly, pattern emerged in time, too, even though second face expected to remain dominant in conscious perception, neurons did not continuously represent that face, instead, their activity rapidly alternated between consciously perceived face and one suppressed from awareness.
This switching occurred around 15 times every second, so, even though second face expected to dominate macaques perception, first face kept flickering through their brains remarkably and repeatedly. And researchers found something else intriguing, during conscious moments, neurons responded more sharply to features of perceived face than to features of suppressed face during suppressed moments, suggesting brain may have way of distinguishing between two, even as it alternates between them.
Findings do not explain how brain decides which information reaches consciousness, but researchers speculate process allows brain to sort through alternative visual information without altering current behavior. Such process might allow us to continue navigating world while brains unobtrusively consider other interpretations of what we seeing, facilitating seamless experience through furious complex neural activity behind closed doors.
Limitations And Fascinating Possibility For Conscious Perception
There are also some important limitations, study involved only two macaques, and they could not report what they were seeing, so their conscious perception had to be inferred from human experiments. Additionally, researchers only investigated specific regions involved in visual processing, not entire brain, nevertheless, results raise fascinating possibility that apparently seamless experience of world is facilitated by furious, complex neural activity taking place behind closed doors of conscious experience.
Identifying mechanisms that orchestrate these transitions, and determining why only some temporal segments become available to awareness, will be essential for understanding how temporal population dynamics give rise to conscious perception, researchers write. Findings, yet to be peer-reviewed, are available on bioRxiv, offering good news that temporal dynamics may unlock basic unsolved problem in neuroscience about conscious and unconscious visual information processing.
Q&A
Q: How many times per second does brain switch between conscious and unconscious visual information according to Berkeley preprint?
A: New preprint involving macaque monkeys humans suggests brain may be switching back forth between conscious and unconscious information around 15 times second, raising possibility something other than visual availability guiding conscious experience world.
Q: What is binocular flash suppression and how did researchers use anaglyph glasses to test conscious perception?
A: Researchers used anaglyph glasses red cyan lenses trick eyes showing two different faces, first presented one eye then suddenly second other eye, brain prioritizes newly introduced face suppressing first from conscious awareness, eye still receiving it.
Q: What did EEG electrodes in face recognition regions reveal about brain activity alternating between perceived and suppressed faces?
A: Tiny electrodes inserted visual processing regions recording hundreds neurons simultaneously identified two distinct patterns linked first face second face, activity rapidly alternated consciously perceived and suppressed, switching around 15 times second, neurons responded more sharply during conscious moments.
FAQ
Q: How does brain determine which visual information reaches conscious awareness and which remains hidden without overwhelming?
A: Brain can deprioritize information famous example nose always middle field view tuned out useful, without it overwhelmed volume sensory input, same brain parts respond unconscious stimuli too, answer may lie not space but time temporal dynamics.
Q: Why did neuroscientists focus on time dimension rather than space to understand conscious and unconscious visual processing?
A: Decades studying which parts brain active when stimuli consciously perceived problem emerged same parts respond unconscious stimuli too, Hesse colleagues asked what if searches focused wrong dimension, way brain activity changed over time might yield clues handling.
Q: What are limitations of macaque study on conscious perception flickering and what future research needed?
A: Study involved only two macaques could not report what seeing conscious perception inferred human experiments, only specific regions involved visual processing not entire brain, identifying mechanisms orchestrating transitions determining why only some temporal segments available awareness essential.
Q: How might rapid switching 15 times second help navigate world while considering other interpretations of visual information?
A: Researchers speculate process allows brain sort through alternative visual information without altering current behavior, such process might allow continue navigating world while brains unobtrusively consider other interpretations seeing, facilitating seamless experience furious complex neural activity behind closed doors.
Q: Where are findings about brain flickering between conscious and unconscious vision available and have they been peer-reviewed?
A: Findings yet to be peer-reviewed available on bioRxiv preprint, team led Janis Hesse Doris Tsao University California Berkeley, involving macaques humans anaglyph glasses binocular flash suppression face recognition regions electrodes recording hundreds neurons simultaneously.
Disclaimer: This article provides educational information about neuroscience, conscious perception, unconscious visual processing, binocular flash suppression, preprint study involving macaques and humans, and does not constitute professional medical, neurological, or scientific advice, diagnosis, or research validation.
