 In the late 1950s and early 1960s, so little was known about how humans would react to spaceflight that researchers had to get pretty creative. And one interesting moment of creativity was recruiting deaf participants for various motion sickness studies. This series of tests was done cooperatively between NASA and the US Navy, and it might sound a little bit weird, but it actually makes a lot of sense when you consider where motion sickness comes from within the body. It all comes down to the vestibular system, which is the system inside the inner ear that's responsible for balance and all kinds of sensory information about movement and orientation in space. Sensitive nerve and hair cells react to the movement of fluid inside the inner ear to give our brains information about motion, balance, and even spatial orientation. Some scientists still think there might be multiple causes for motion sickness, but one of the most commonly agreed upon causes is called sensory conflict theory. Think about when you read in a car if you get motion sickness. Your eyes, looking at the book, don't see any movement, but the fluid inside your inner ear is aware that you're moving forward. This sends conflicting information to your brain, you get nauseous, and then you throw up, which is deeply unpleasant for anybody. A similar thing happens in space when astronauts get space sickness. The vestibular system suddenly doesn't have the same cues of up and down or motion because they're weightless, but the eyes see things as being quote-unquote normal and that you can still read a book. So you still get that conflict of information that can lead to nausea and vomiting, which is what nobody wants in space. Not only can you not exactly air out a spacecraft very easily, but if that liquid clumps up and gets into a control panel, that can be a very bad day for electronics. Not to mention means that you can't do space walks and it means that you'd have to shift around the schedule to account for a sick astronaut. NASA knew this could be an issue, so it's said about trying to understand how people react to stimuli that can involve motion sickness, things like high gravity acceleration and then zero gravity. To understand the broad spectrum of how people might react to motion sickness or the situations that could invoke motion sickness, NASA tested 11 deaf individuals. The way they became deaf is really important here. Of these 11 deaf men between the ages of 25 and 48, all but one was deaf after childhood bout with spinal meningitis. Spinal meningitis can, among other effects, cause lasting damage to the vestibular system of the inner ear by killing those sensitive nerve and hair cells that we need for that sensory information about balance, motion, and spatial orientation. That meant that these men had the vital system involved in motion sickness, the vestibular system damaged, and they were, theoretically, completely immune to motion sickness, so NASA tried to make them motion sick. There were a series of tests done with these men throughout the 1960s, and some of them sound really pretty awful. In one test, four men were put into a room where the walls spun at 10 revolutions per minute for 12 straight days, and not one of them got motion sick. In another test, a number of the deaf men were put on board a boat with 20 men who could hear, so their vestibular system was intact, on a boat that was sailing in very choppy waters off the coast of Nova Scotia. The men played cards and generally felt fine, while 15 of the 20 men who could hear all got violently ill. In fact, the deaf men had no motion sickness. Not even when the choppy waters got so scary that they all feared shipwreck. Even the panic couldn't induce any kind of nausea in these men. Another test had them floating around in the infamous vomit comet, the plane that flies parabolas to give you short bursts of weightlessness. And it's called the vomit comet because most people throw up. But these men didn't throw up, and when researchers tested their urine after the flight for the presence of stress hormones, they found none, whereas the men who could hear who did the same test did have raised levels of stress hormones in their urine. So it really did seem like these men were just completely immune to motion sickness. It was a very odd and very unique and very interesting series of tests that NASA did in cooperation with the Naval School of Aviation Medicine in the 1960s. And ultimately, these 11 deaf men played a massive and unsung role in helping get humans off the earth. If you love learning weird little tidbits about space history, be sure to subscribe to this channel because I do regular videos telling you all the things you never thought you even wanted to know about old-timey spaceflight. And of course, as always, I have a little bit more about this story on my companion blog post over at Discover. The link is in the description below if you are curious. I also want to remind you guys that you can now sponsor Vintage Space to help make the content that you love possible. There's a video about how that works right up here. So of course, leave me any questions, comments, and concerns that you have in the comments down below. Is there anything you'd like to see covered in a future episode? Any question that I didn't quite answer? Let me know all of your thoughts. And of course, you can follow me across social media, Facebook, Twitter, Instagram for daily Vintage Space content. As always guys, thank you so much for watching and I'll see you next time.