Perceptual balance and sea legs

[DaveC426913]

perceptual balance and "sea legs"

I'm sure everyone has experienced this. After coming off a boat trip of several days, I feel like the soild ground under me is swaying as if I'm still on waves. This can last for days.

What I wish to understand is what in the brain is causing this perception of balance once it is no longer being stimulated? I assume the brain has sort of temporarily rewired itself to help the eyes and muscles compensate for a pitching deck, so I can see how you'd get used to it after a few days at sea, but what exactly causes the brain to falsely create that sensation on flat ground when there's no stimulus remaining, and why?

 

[Schrodinger's Dog]

It's an inner ear thing, you have a liquid in your inner ear that tells you whether your upright, upside down or swaying from side to side according to the nervous stimulous within this cavity, this feeds to your brain so if you get used to it, your brain assumes this is the norm, it takes a while for your inner ear to come back to normality, so you will tend to have sea legs for a while. Might be wrong but that's the way I understood the feeling.

Try taking a ride on wurlitzer, it'll demonstrate this effect quickly, your brain is telling you your going round and around and up and down at speed, but as the inner ear adjusts you slowly come back to normal gravitational affect, but you'll feel like the ground isn't in the right place, so you'll stumble around for a bit. It may make you feel sick also, it did me, but then I'd just eaten

 

[DaveC426913]

... this feeds to your brain so if you get used to it, your brain assumes this is the norm, it takes a while for your inner ear to come back to normality, so you will tend to have sea legs for a while...

Yes, exactly like I'm thinking.

But upon closer examination, that doesn't actually answer the question.

There's no connection between the cause (your brain gets used to a pitching deck) and the effect (your brain inserts a pitching deck feeling when there is no pitching deck). Saying "your inner ear takes a while to come back to normality" is hand-waving the cause/effect.


I'll propose two, wild, unrelated hypotheses, because I just haven't been able to think of anything logical:

Hypothesis 1] Your brain, while at sea, is confronted with conflicting information from your eyes, your feet and your inner ear about where the horizon is and where the deck is. These inputs are no longer to be trusted in this regard. So your brain decouples these stimuli.

When you get back to land, your brain still has these senses decoupled, and these independent, multiple sensory attacks can once again lead to conflicting interpretations. It is this conflict of interpretation that feels like a rocking motion.

This hypothesis supposes an illusion - a "bug", a mistake in the brain's interpretation of input.



Hypothesis 2] Your brain, at sea becomes hypersensitive the smallest rocking motions (which is a useful adaptation to anticipate a pitching deck so you don't trip all the time).

The brain becomes so sensitized to motion that it can pick up the motion of your body from your pulse. (Before you dismiss this, know that it is QUITE possible in certain postures to not only feel your pulse moving your body, but to even see the rocking motion visibly. eg., if you are cross-legged and hunched over, the big arteries in your abdomen will cause this and you can see it happen.)

This hypothesis supposes, not an illusion, but a bona fide perception of a real phenomenon.

 

[hypatia]

Also keep in mind, nerve endings in the otolithic organs{inner ear} are embedded in a gelatinous membrane known as an otolithic membrane. Embedded in this gelatinous membrane, like grapes in fruit jello, are the otoconia. They are tiny calcium carbonate/calcite crystals. Their whole purpose in life is to make that jello as heavy as possible. That way, when you tilt your head in a gravitational field, the otolithic membrane moves accordingly, thus stimulating the nerve endings underneath.

Getting your land legs back, may just be a matter of letting this gelatinous membrane, along with the crystals settle down.

 

[DaveC426913]

Getting your land legs back, may just be a matter of letting this gelatinous membrane, along with the crystals settle down.

Right, but that would suggest that, while on the boat, they are not settled down, thus you should continually experience disorientation during your watery vacation until they are no longer being "unsettled".

 

[Mk]

I'm sure everyone has experienced this. After coming off a boat trip of several days, I feel like the soild ground under me is swaying as if I'm still on waves. This can last for days.

What I wish to understand is what in the brain is causing this perception of balance once it is no longer being stimulated? I assume the brain has sort of temporarily rewired itself to help the eyes and muscles compensate for a pitching deck, so I can see how you'd get used to it after a few days at sea, but what exactly causes the brain to falsely create that sensation on flat ground when there's no stimulus remaining, and why?

I think it might be psycho-something too. I am under the impression I am very susceptible. One time I spent a few hours in a pool. When I got out, if I lifted my arms up, they felt very light, exactly like they feel if you let your arms float while you stand up in a pool. After riding a rough roller coaster (Sheikra), when riding in the car, every time the road dipped (inches to feet) I felt weightless.

Based on my experiences, I'd go with Dave's Hypothesis 2]

Your brain, at sea becomes hypersensitive the smallest rocking motions (which is a useful adaptation to anticipate a pitching deck so you don't trip all the time).

The brain becomes so sensitized to motion that it can pick up the motion of your body from your pulse. (Before you dismiss this, know that it is QUITE possible in certain postures to not only feel your pulse moving your body, but to even see the rocking motion visibly. eg., if you are cross-legged and hunched over, the big arteries in your abdomen will cause this and you can see it happen.)

This hypothesis supposes, not an illusion, but a bona fide perception of a real phenomenon.

 

[Mk]

Actually it was a day of riding rollercoasters. I went five times I think.

 

[Schrodinger's Dog]

Yes, exactly like I'm thinking.

But upon closer examination, that doesn't actually answer the question.

There's no connection between the cause (your brain gets used to a pitching deck) and the effect (your brain inserts a pitching deck feeling when there is no pitching deck). Saying "your inner ear takes a while to come back to normality" is hand-waving the cause/effect.

.

Actually what I meant to say, it takes a while for the brain to get used to the normal non pitching and rolling when it has been compensating for so long, this pattern though is consistent with many stimuli, the body adapts, when it no longer needs to adapt it needs to retask so to speak, there is a period of time of adjustment while the brain "reprograms" back to normal.

I think your over complicating something fairly simple, we learn to adjust to the pitch and toss, then when it is no longer pitching and tossing we have to learn to adjust to that too. I suspect the reason there isn't cavernous research into this are

1) it has no practical purpose

2) they simply assume that with all abilities that are learned in a feedback loop, that relearning how to do something the old way whether conscious or unconscious takes time. It simply appears to be the way we are programmed, I like what your saying but I'm not sure you aren't just overcomplicating the whole deal. Unless you mean how does the brain learn, then your in for a world of complextity.

Your brain inserts a compensating effect which is probably quite analogue and adapts fairly quickly once the mechanism in place, which enables you te remain steady despite the pitching and rolling, what your feeling is a compensating effect, which to all intents and purposes negates the unbalancing effect of the rolling and pitching. The brain is looking for a stimuli and responding as if that stimuli were present to counter act, then it simply learns gradually to adapt to the new stimuli.

EDIT: I had to write this in three parts, so I hope it never confused anyone. Being at work you know, outrageous that they expect me to actually do work!

 

[Moonbear]

That's an interesting question. Though, I've never experienced it last for more than a few hours, it also doesn't take a few hours to adjust to being on a rocking boat (at least not for me), so simply saying it's an inner ear effect doesn't cut it.

I don't really know the answer to this question, though, like you, would speculate it's an adaptation either of sensory receptors (sort of like when everything sounds muffled after you've been at a loud concert), or something higher in the brain that changes to compensate for the motion (I think it's as interesting that you can adjust to the motion faster than you adjust to standing still again).

Anyway, I'm going to move this topic over to the Mind and Brain forum, because I suspect your answer lies there more than it will with just inner ear function.

 

[Schrodinger's Dog]

That's an interesting question. Though, I've never experienced it last for more than a few hours, it also doesn't take a few hours to adjust to being on a rocking boat (at least not for me), so simply saying it's an inner ear effect doesn't cut it.

I don't really know the answer to this question, though, like you, would speculate it's an adaptation either of sensory receptors (sort of like when everything sounds muffled after you've been at a loud concert), or something higher in the brain that changes to compensate for the motion (I think it's as interesting that you can adjust to the motion faster than you adjust to standing still again).

Anyway, I'm going to move this topic over to the Mind and Brain forum, because I suspect your answer lies there more than it will with just inner ear function.

I didn't say that it was an inner ear effect, I said it was a feedback loop between brain and inner ear, that's indeed what I meant originally when I used the term, I just screwed up the description as I was in a hurry.

The brain adjusts to the pitching and rolling by creating a compensation effect which by adjusting to the rhythm of the pitching and tossing, stops the inner ears nervous signals from becoming activated so much, this in turn feeds back and forth until the brain learns the path of least sensitivity for the inner ear*, to compensate to the waves effects on the vessel, this is an analogue process that can adapt to the tossing of the vessel which generally isn't dramatically altered over time, there are subtle shifts between intensity of movement and direction, but the ear can compensate if they're not too radical. This compensating effect is again mostly subconcious, when we are treated to a level surface again though the brain is still reacting to compensate for the waves, which of course is just the opposite of what you were experiencing on the boat when you first climbed aboard, and so it feels like the land is moving again. In a few hours your back to normal again, the brain adjusting more quickly to an easier more level surface.

I tried to explain that in my second post a bit but didn't have time so I wasn't specific about what I meant by a feedback loop. I think it's an interesting hypothesis, I think it even makes sense, at least to me, but since I am unlikely to ever be a researcher in the field what I think is meaningless

Feel free to criticize my notions after all they are speculatory and not based on a deep understanding of how the brain reacts to stimuli.*This means that the bodies position adjusts automatically and often subconciously given enough time according to what the brain is working out about the motion signals it is getting from the inner ear, which give it a crude but effective 3 dimensional representation of motion.

 

[hypnagogue]

I'm not sure what the exact mechanisms involved might be, but I suspect that this is just an instance of sensory/sensorimotor adaptation, not very much unlike any other kind of sensory adaptation. I guess the general principle is that the brain, when given a constant kind of sensory input, adapts such that that input becomes a kind of baseline condition that is largely unnoticed in perception. When the chronic stimulus is removed, the sensory situation becomes displaced relative to the previously formed baseline, and so the absence of the stimulus becomes conspicuous in perception until the brain has time to readjust its sensory baseline.

A simple example is adaptation to a loud, constant noise in the environment, like the hum of an old air conditioner. Upon turning on the air conditioner the noise it generates will be perceived as conspicuous, but after some short time it seems as if there is no noise in the background, or at least it goes largely unnoticed when not explicitly attended to. Upon turning the air conditioner off, the ensuing silence then might seem conspicuous to you until you've had some time to adjust.

That is just a relatively mundane everyday example, but sensory adaptation can work in really remarkable and complex ways. For instance, George Stratton invented a pair of glasses that inverted the light rays hitting the retina, such that the world appeared upside down. After a series of days wearing the glasses, Stratton reported actually adapting to the odd input such that the world appeared rightside-up again. Finally, after removing the glasses, the world again appeared to be flipped upside-down, and it took several hours for his vision to return to normal.

 

[mahesh2000]

it seems to me that comparing the balance system and our eyes, getting your sea legs is like light adaptation (FAST) and losing your sea legs is like dark adaptation (SLOW).

light adaptation is a FAST process. this is what happens when you step out of a matinée movie and things are too bright. within seconds, your eyes adjust to the glaring brightness outside.

dark adaptation is a SLOW process. this is what happens when you go into a dark room with faint light in it. this can take up to half an hour. your eyes slowly adjust to the darkness.

see http://webvision.med.utah.edu/light_dark.html" .

why this might confer an evolutionary advantage, i do not know.

 

[Cincinnatus]

It is quite interesting to me that the original poster (I see this was an old thread) claims that the "sea legs" phenomenon can last for days. I've experienced it myself, but only after short trips and it has always faded after a minute or so. My experience is more inline with the time courses of deadaptation we observe in psychophysical experiments where we have subjects adapt to an unusual force environment then remove it.

For example, we perform experiments where subjects adapt to make accurate reaching movements while holding a robotic manipulandum imposing a velocity-dependent force on their arm. When the force is turned off, mistakes are initially made, but within 10 movements (often less) after the force is turned off the subjects are moving normally again.

It is possible that the OP's reportedly long timecourse of deadaptation could be due to having been exposed to the unusual environment (the rocking of the ship) for an amount of time much longer than we use in these experiments. According to some theories of sensorimotor control we might say that his internal model of how his intentions translate into actions while on the ship was active for so long that it replaced the old internal model of how his intentions translate into actions on solid ground.

 

[mahesh2000]

...the original poster ... claims that the "sea legs" phenomenon can last for days. I've experienced it myself, ... and it has always faded after a minute or so. My experience is more inline with the time courses of deadaptation we observe in psychophysical experiments where we have subjects adapt to an unusual force environment then remove it.

my personal experience is that it can easily last 24 hours. i went sailing yesterday, and still have my sea legs this morning. i am not sure how long it lasts as i go sailing everyday. it is certainly of the order of a day or more, not just a few minutes.

 

[SpicyRamen]

I'd go with Moonbear's answer,
It's probably an adaptation of our sensory receptors.
Since you were on the boat for several days,
your body accepted that as the norm of the situation,
so when you got back on to rock solid land
It was a shock to your sensory and it feels weird.
It would be as if you had walked from solid land onto jello
your senses need to adjust.

 

[DaveC426913]

I'd go with Moonbear's answer,
It's probably an adaptation of our sensory receptors.
Since you were on the boat for several days,
your body accepted that as the norm of the situation,
so when you got back on to rock solid land
It was a shock to your sensory and it feels weird.
It would be as if you had walked from solid land onto jello
your senses need to adjust.

Yes, that is the obvious answer. But it does not go deep enough.

What I've been trying to get at is that the feeling you have - that you are still rocking - makes no sense.

See, in an optical illusion, when you exhaust one colour (say, red) you are hit with the complementary colour (blue-green). This is logical because if you take the baseline (which is essentially white) and remove the red (because those receptors are exhausted) what you are left (the receptors that are active) is blue-green.

But there's no real "complementary" counterpart in a feeling of rocking motion.

 

[mahesh2000]

i was misunderstood: even if i go sailing for a few hours, the rocking motion lasts for at least a day. it takes about 2 days for the sensation to stop. daveC has a point about complementary colors. however, i wonder if the answer lies within his analysis. perhaps without the stabilizer, the liquid in the ears sloshes around, generating a rocking feeling. this rocking is wiped out with appropriate damping (similar to Bose's noise canceling headphones?). when on a boat, the damping circuit might be turned off temporarily, and takes time to turn back on.

hm, reading that, it sounds like a load of baloney... i don't convince myself.

 

[mahesh2000]

drinking too much alcohol produces the same feeling. i wonder if the two sensations come from the same place.