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Comment by xwdv | Hacker News Reader

I’m not sure what they expected? Which way is a cat supposed to auto-right to in a weightless environment?

But a cat free-falling from a height is also weightless, and yet they manage to right themselves using perceptual cues. The point of the experiment is to see how the behavior changes when the sensation of weightlessness is presented for an extended period of time, without the "falling" motion (relative to the perceived local environment) that normally accompanies it.

This is what most of the people replying here are missing - all falls are "free fall" (zero g).

Yes the cat manages, but not in this situation.

The cat's system has memory. The transition into free-fall from a state where it was previously experiencing ground reaction force provides a cue for the self-righting reflex on the direction of "up/down". Apparently even blind cats can self-right based on their vestibular system.

The cat might use visual cues to right itself.

It might have been interesting to re-run the test with a more obvious "horizon" and see if the cats react to that. Then if the cat still doesn't right itself, it seems like it is using acceleration rather than vision to determine which way is down.

Do we know it's visual? If you drop a cat in darkness (onto a pillow of course), will it right itself? What if you put it in an elevator that accelerated downwards at 1G so the cat fell to the ceiling? How does it know which way is down? Is it the horizon, or the bright sky, or does the cat remember the scene before it was dropped? Or is it the air rushing by?

> Then if the cat still doesn't right itself, it seems like it is using acceleration rather than vision to determine which way is down.

This is not possible because objects (including cats) in freefall do not experience the sensation of acceleration.

I think that's the point, they do not experience acceleration in zero g, which is the point of testing visual/aerial cues, which DO remain in free fall (electric fans, horizons).

I'm fairly sure you just read this backwards, thought I'd explain better.

This is interesting because, it provides information on how the cat brain might function - if they have accelerometers embedded in their brains, that is quite interesting, but somewhat unlikely (birds have magnetic sensors, not impossible or unprecedented), if, perhaps more likely, they have incredibly sensitive hearing or sensation on their fur, which they interpret as acceleration, that is also interesting, in a different way.

Before a cat (or any object) experiences free fall, they experience acceleration so they know which way gravity is pulling them. Surely, a cat can remember what happened to it in the last few seconds and instinctually put its feet in that direction?

You don't feel any acceleration from gravity - it can only be determined from other senses like vision or the air flowing over your skin/fur

What about inner ear sensations? Or the pressure of your organs pushing against one another?

None of the above. This is because every atom in your body is accelerating at the same rate, so there's no pressure involved.

This is possible because in free fall on earth, there are directionality signals when blinded - for example, air resistance.

Any fall is a weightless environment, whether it's in a plane or off a building.

But in a plane, you don't have the air rushing past your whiskers.

Probably the same reason as discussed here recently: A naked skydive inspired a way to keep pilots oriented in flight (military.com) https://news.ycombinator.com/item?id=30959126

Edit: Probably that submission led to this one.

Reply on news.ycombinator.com