That's just it, the real horizon will appear to move even though it's the vehicle moving. People tend not to get seasick/motion sick when they can see the outside apparently swaying because that coincides to the bumps they feel. It's when they are entirely inside or focused on on something that isn't moving relative to themselves that there is a difference between feel and vision.
While I don't get seasick at all, I'll add this in so that someone might try it. I noticed that on a rocking boat people stand two different ways. Most people will move their feet apart and assume a rigid stance so their head is always up relative to the boat. Others will keep both feet together and stay upright relative to gravity, seemingly tilting back and forth in rhythm with the ship. I suspect the second might help with motion sickness since you would see the boat move like you feel that it should. It always struck me as funny to have some of both types in the same group having a conversation.
Hmm, I thought the problem was that the acceleration of the car (for example sideways acceleration when going through a bend) was perceived as a sideways component of gravity – as the principle of general relativity tells us, they are the same thing – without there being a corresponding visual input, even when looking outside. In contrast to something that replicates the actual horizon, the blue liquid in these glasses would feel and adapt to the same sideways acceleration as your body feels, so I thought that was the point.
While I don't get seasick at all, I'll add this in so that someone might try it. I noticed that on a rocking boat people stand two different ways. Most people will move their feet apart and assume a rigid stance so their head is always up relative to the boat. Others will keep both feet together and stay upright relative to gravity, seemingly tilting back and forth in rhythm with the ship. I suspect the second might help with motion sickness since you would see the boat move like you feel that it should. It always struck me as funny to have some of both types in the same group having a conversation.