Thanks to Linode Cloud Computing for  supporting this episode of SciShow.

Head to linode.com/scishow to learn more and get a $100 60-day credit  on a new Linode account. [♪ INTRO] Eyes perceive light, ears  perceive vibrations in the air… and our inner ears perceive gravity. It’s easy to think of gravity as  something that’s just kind of there, keeping us stuck to the Earth and not much else.

But scientists are learning that it’s  also a key player in our perception. It seems to be baked deep into how  our brains process things like motion, interacting in surprising ways with  how we process the world around us. So much so that scientists are beginning to wonder how it might affect how we  process other worlds, too.

Let’s start with how we sense gravity. This is primarily done  through the vestibular system: a series of fluid filled canals  and sacks in our inner ear. When we tilt our head, tiny hairs within  these structures bend and sway under the force of gravity, with different hairs  responding to bends in different directions.

The brain takes the combined  signal from all of these, and uses it to work out the direction that  gravity is pulling us, relative to our skull. Anyone who’s spun around real fast as  a kid… or adult… can attest to this. You get dizzy, you lose your balance, and  gravity feels like it’s playing tricks on you.

We might even perceive the  world to be spinning around us. But that’s not the only way  in which how we sense gravity can mess with our perception of things. Having a sense of where objects are being pulled, and how strongly, can affect how  well we can interact with them.

Studies have shown that there are  differences in our ability to track moving objects that move according  to different strengths of gravity. One experiment which investigated this  published in 2015 tracked participant’s eye movements as they attempted to “catch”  digital falling objects under different gravity conditions: typical Earth gravity,  weightlessness, and double Earth gravity. For some of the trials, part of the path  of those falling objects was hidden.

So the participants’ brains had  to work overtime to figure out when they’d reappear in order to intercept them. When analyzing those eye movements,  the researchers found that the participants were better able to smoothly  track objects falling according to Earth’s gravity than those moving in  weightlessness or double gravity. Researchers in the field believe that this  difference points strongly to the existence of an internal understanding  of gravity in our brains, which influences the way  we expect stuff to behave.

This internal model also doesn’t  appear to be influenced by what we know about the things we see. In a paper from 2020, researchers  showed that, regardless of which way we expect an object to move, we’re  better at judging how quickly they go when they move towards gravity,  compared to away from it. To do this, they asked participants to view  the surface of a virtually generated planet.

On this other-worldly scene,  there were two objects, both displayed to be the same size: a rugby ball, which, for those of you not into  sports-ball, looks like this, and a rocket. Participants were asked to watch  the objects move between two bars, and then judge whether they were moving  faster or slower in subsequent trials. Now, the key here is that you’d expect  a rocket to go up and a ball to go down.

But the results showed that participants  were better at judging the speed of both objects when they were moving downwards. From this, the researchers concluded  that our sense of gravity works independently of semantic information  we already know about objects, like the fact that a rocket  generally goes upwards. However, there were a few limitations they  didn’t rule out, so more study is needed.

Lucky for us, there’s a whole field for that. And it’s not all about how inanimate things fall. Research suggests that our sense of gravity can also change how we process things  like other people’s body movements.

In a study published in the  European Journal of Neuroscience, researchers found that it’s not  just the movement of objects that are subject to our sense of gravity. Bodily motions are too. This team asked participants to watch  a series of point-light movements, which are basically a cluster of  moving dots often used by researchers to simulate bodily movements,  without much unnecessary detail.

Some of these were random, with no  particular movement pattern at all, whereas others were arranged  to look like human movements. The participants watched these  both in a relaxed upright position, and in a chilled-out tilted  position on a tilt table. They were always shown the groups of dots  at the same angle relative to their bodies.

But since the participants’  body positions were different, the two conditions varied relative to where  the participants perceived gravity to be. The participants were asked to pick  out whether the point-light movements they were watching were random  or looked like a person moving. And they were generally pretty good at it.

After all, for most people,  it’s not a tricky task. But crucially, when they were tilted,  they were significantly slower at deciding whether patterns  showed biological motion or not. The researchers believe this could indicate  that our ability to perceive biological motion doesn’t just rely on the visuals  of the motion itself, but how much they match up with where we perceive  gravity to be in any given moment.

Knowing all of this gives us a better  understanding of how our senses work, which is always a plus. Getting a better handle on all the  moving parts of our cognition helps us to not only better understand  how we perceive in general, but also come up with treatments  when things go a little wrong. But many scientists in this field  are wondering what this might mean for humans who travel into space.

Under different gravity conditions, astronauts could be perceiving  things in ways we never expected. It’s possible that this could  lead to some extra difficulties performing intricate tasks, which  scientists may need to look at mitigating to make sure their  jobs are as easy as possible. Research in this area is still pretty young.

But in the future, knowing how gravity  can affect our understanding of the world around us could make space exploration  easier on those doing the exploring. And maybe back here in Earth’s gravity, too. Thanks to Linode Cloud Computing  for supporting this video.

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