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Comment by leereeves | Hacker News Reader

> Your legs are moving but your head / vestibular system isn’t experiencing acceleration that it expects with those leg movements

That's also true on a treadmill. I think the bigger problem would be that the world appears to be moving (unlike a treadmill) and you don't feel any acceleration.

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So can I use the Disney system to simulate running on a treadmill?

You don't get motion sick on a treadmill because you're not wearing a VR headset. There's no forward motion of your head captured with your eyes to mismatch what your vestibular system is feeling.

To add to your point, there is a somewhat unpleasant sensation once you get off the treadmill, i.e., even if you are standing in place, it feels like you are moving forward.

This reminds me of the similar weird sensation of phantom movement after jumping on a trampoline.

This is incorrect. You don’t get motion sick on a treadmill because the small accelerations and decelerations match what your eyes are seeing. There is motion.

I agree there's motion, I'm saying there isn't a mismatch with what your eyes are seeing, which is what causes the motion sickness

I actually do get a bit of motion sickness when I get off a treadmill. It takes me a couple minutes to get my bearings after stopping.

But on a threadmill you're going in a straight line and usually at constant speed. A constant speed, you don't have acceleration.

Exactly, you don't have acceleration, and the world around you isn't moving relative to you, so there's no mismatch.

The treadmill shows that performing the walking movements without acceleration doesn't generally cause motion sickness.

> you don't have acceleration

If you actually use a treadmill, or watch motion capture, you’ll see that this isn’t the case. It’s a lot of slight accelerations and decelerations. The variation change from person to person, and more experienced runners are able to minimize them, but they’re still present.

Edit: this study is peripherally related https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8160945/

> It’s a lot of slight accelerations and decelerations

Isn't that always true? If I pay attention to it, I notice a lot of tiny movements of my head, as I just sit here typing.

"You don't have acceleration" is just talking about the big accelerations from 0 mph to roughly 3 mph to 0 mph, not implying that you're completely motionless as if frozen in ice.

Acceleration is change in velocity and change in time, either can effect the apparent amount of acceleration. The velocity you accelerate to or from is just an implementation detail.

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