When Your Eyes Can’t See, but Your Brain is Still Watching

of all of the sensory inputs that make up the way our brains process and experience the world none are as important as vision it's estimated that site accounts for 80 to 85 percent of learning perception and cognition leaving hearing to make up 11 smell with 3.5 percent touch with 1.5 percent and taste with just one percent this might sound like an exaggeration but just consider the way that sound travels much more slowly than light we can often see lightning before we hear the thunder that accompanies it our vision gives us access to things farther away than all other senses too we might be able to smell things in our general vicinity but to taste or touch anything it has to be in direct contact with our bodies so for people who don't have the sense of vision it might be easy to assume that the perception of the world is dulled or at least that they have to navigate the world with far less information but it turns out the human brain has the remarkable ability to adapt people who are born blind or become blind early in life often have a more nuanced sense of hearing and they can extract more information from sound than people with sight and for some people this information extraction from Sound reaches extraordinary levels for some people sound provides the brain with information in much the same way that light and vision does in their Mind's Eye a picture is formed and for certain other people without sight even if their eyes can't see their brain is still watching their brain is watching so much that they can avoid obstacles in their path sidestepping zigzagging and dodging things as if they could see but with no awareness that they're dodging anything at all how is it that their brains can seem to process visual information without being able to see how is it that sound can form pictures in the brain why is human Vision so much more complex than meets the eye [Music] if we start with the most basic elements of the eye you'll know that we have a lens called a cornea on top the whites of our eyes called the sclera a pupil through which light enters a colorful Iris that opens and contracts to change the amount of light that gets in and a retina in the back of the eye to absorb that light and with vision this light is everything it's the stimulus input needed for the brain to see the world around it light is a form of electromagnetic radiation and the human eye can perceive wavelengths between 400 and 700 nanometers a narrow sliver of frequencies that exist between infrared and UltraViolet on the back of the human retina are different kinds of photoreceptors three varieties of cone-shaped receptors allow us to perceive red blue and green light while rod-shaped receptors help with vision in low light settings when light passes through the eye it travels into the brain via the optic nerve which heads first to the thalamus and then onto the primary visual cortex at the back of the brain finally that processed information goes to the prefrontal cortex which combines information gleaned from our senses with emotions and memories but there are a lot of other ways the brain is involved in creating a comprehensible picture from the information our eyes provide to our brain because even for those of us with perfect vision what we see is largely an illusion consider blinking for example we blink so frequently that we spend about 10 percent of our waking hours with our eyes closed yet we rarely have the sense of our vision being interrupted by those movements of our eyelids and that's because the brain is filling in the gaps or there's the fact that we actually have enormous blind spots in each of our eyes obscuring an area the size of four outstretched fingers and yet we don't perceive any holes in our vision at all our brain just fills in the blanks without us really noticing or there's the fact that the center of our visual field the fovea is far more accurate than our peripheral vision but we still have a sense of perceiving what's on either side of us once again thanks to the brain we get the sense that our eyes are able to see more accurately than they actually do our brains are constantly creating pictures of things that we can't actually see with our eyes and for some people without sight their brains do much more creating entire maps of their surroundings with no visual input at all when echolocation was first invented as a scientific term in 1944 it was used to describe the way bats navigate their environment and it was thought that surely this was a skill reserved for these creatures who fly and hunt in the dark it was thought that blind members of our species had to rely on touch to get around but as far back as 1749 French philosopher Dennis didero noticed something interesting he described a blind acquaintance who was capable of locating objects and obstacles and estimating their distance at the time didero thought it had something to do with feeling the presence of the objects on their face due to pressure changes however as we developed more rigorous forms of scientific testing researchers realized that if the ears were blocked blind participants could no longer detect an obstacle and judge its distance so it wasn't the tactile Sensations on their face that they were using but rather their ears in fact these researchers noticed that some blind people used clicks to produce Echoes that they then used to judge the distance shape and texture of objects in their surroundings they weren't simply passively listening to their environment but actively echolocating and doing so allowed them to effectively navigate the world around them some people with this ability were managing to explore cities hike play some sports and even mountain bike the scientists realized that they had to completely reconsider what it meant to be blind but what is actually happening inside the brain during echolocation is it basically just an enhanced sense of hearing scientists couldn't be sure until they started using MRI machines to visualize the brains of blind people who use this form of clicking to navigate their surroundings and they found that what's happening in the brain is less like normal listening and much more like what happens when sighted people use their eyes to interpret light one experiment to put five blind people five-sided people and Five Blind echolocators and an MRI and then played a series of recordings of a clicking sound bouncing off an object at different places in the room the blind non-eco locators and cited people's brains lit up in the auditory processing regions when hearing The Echoes but for the blind echolocators it was the visual part of their brain that lit up in precisely the same way that happens inside of people when they looked at their surroundings in other words these blind echolocators are able to build visual maps without ever using their eyes but this wasn't the case for blind people who had no experience with echolocation which ruled out the hypothesis that blindness alone is enough to Grant this ability but that doesn't mean it's an Ability Beyond their reach other studies on the effectiveness of click-based training programs have shown that people can learn to echolocate over the course of a 10-week training program the vast majority of participants in these programs report an increase in Mobility Independence and well-being but when people echolocate it's not like they can see again it's been described more like an acoustic flashlight turning on and off with every flash or every Echo objects come more into Clarity and focus with their three-dimensional geometry becoming clear everything from the position Dimensions density and texture are picked up and envisioned in the brain but what happens when the visual cortex in the brain is damaged the eyes might remain unharmed but wouldn't they be rendered mostly useless thanks again to the brain's remarkable ability to adapt this is not always the case in the aftermath of World War One a huge number of young men were suffering from severe injuries including many to the Head doctors saw a number of patients with damage to their primary visual cortex who suffered partial or full blindness as a result even though their eyes were unharmed their brains couldn't process visual information except in some cases they still seemed to be able to do so some patients could still move their eyes towards stimuli like movement or light even though they consciously couldn't see it some could even Flinch when something moved towards them quickly but if you ask them about it they would say they didn't see anything at all this strange ability came to be termed blindsight it has proved a fascinating and complicated source of inquiry for decades one patient who couldn't see anything left of his nose was still able to guess whether lines on a paper were horizontal or vertical and was cracked more than 80 percent of the time a far higher proportion than random chance another patient who was fully blind due to damage to the primary visual cortex was told to walk down an empty hallway except it wasn't empty as doctors filled it with obstacles the patient avoided all the obstacles and completed the walk but at the end still thought that it had been empty it seems to come down to the difference between our conscious perception of vision versus our unconscious perception when the visual cortex is damaged it's the visual experience that is lost how can we explain this some researchers say blindsight is not true blindness because there might be parts of the visual cortex that are still functioning and providing just enough degraded visual information for the research participants to test well in experiments but others have suggested it works because the primary visual cortex is only one component of how our brain processes visual stimuli there are other quieter regions of the brain processing information in an unconscious way scientists think that the thalamus is involved in this and a region called the human middle temporal complex or HMT plus MRI scans of patients with blindsight showed an increased sensitivity to speed and motion in the HMT plus region which wasn't apparent in those without blindsight and Recent research also suggests that there's an independent pathway in our brains that goes from the eyes to the thalamus straight to the amygdala the brain region responsible for processing emotional information this pathway completely bypasses the visual cortex it's a neural shortcut so to speak and scientists think it might have evolved to allow for Rapid threat detection that is separate from and faster than what we consciously perceive but there's a lot we don't understand about the brain yet and there are many other examples of the brain compensating for vision loss in unusual ways take another Vision related case called The Charles Bonnet syndrome which is extremely common in people who are rapidly and progressively losing their vision due to things like macular degeneration about half of people with this kind of vision loss will experience hallucinations of All Sorts some might just see shapes and lines others will see past memories people buildings Landscapes or places and doctors don't understand what the underlying mechanism is apart from being related to the loss of vision in most cases the hallucinations resolve within a year to 18 months but it definitely makes you wonder what the brain is getting up to despite the incredible plasticity of the brain when it comes to vision loss there are still plenty of efforts being made to better understand and reverse it scientists have turned to everything from gene therapy like crispr to bionic eye implants that could provide a limited amount of vision to those who have lost all sight other medical experts are investigating electronic devices that could stimulate the remaining nerve cells in the visual cortex to allow patients to see one test of a microelectrode implant on a blind woman allowed her to identify lines shapes and simple letters we might someday get to the point where blindness can be altogether reversed but maybe for those who have access to training in echolocation there won't be as much of a need the human brain is the most complex form of matter in the universe made up of a hundred billion neurons the number of possible permutations and combinations of brain activity exceeds the number of atoms in the universe there is no wonder that it's constantly surprising us with its capabilities and for those of us who consider ourselves to even have just an average brain in the right circumstances we too are capable of more than we realize I personally get overwhelmed trying to learn certain science and math topics and used to give up thinking it was all just too hard for me but recently I've been using brilliant.org which provides exactly the right environment for me to learn things I thought were Out Of Reach I've always struggled with 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Channel: Real Science

Views: 190,003

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Id: K_MvDo7spEs

Length: 15min 46sec (946 seconds)

Published: Sat Jun 24 2023