Why do I still "feel" ship motion days later?

[Roadfood]

I recently returned from a two-week cruise, and for over two days afterwards both my wife and myself experienced that it “felt” like we were on a moving ship even though we’re on solid ground. Not surprisingly, it’s especially noticable when I lay down; the sensation that the bed is gently rolling back and forth is amazingly real. If I close my eyes, I could swear that I’m still on the ship.

What causes that? Is there a physiological cause, or is it all just “imaginary” (the mind gets so accustomed to the motion that it somehow creates the sensation long afterwards)? Certainly, it can’t be that the fluids in my inner ear are still sloshing around after two days. Has any serious medical research been done on this? I tried searching the web, but I can’t seem to come up with good keywords for this.

[Gary_T]

Sounds like you’ve still got your “sea legs.” I don’t know the details, but apparently the body and brain subconsciously adjust to the motion aboard ship, and it takes some time for them to readjust to the lack of said motion. The notion of “sea legs” and “land legs” goes way back. I recall reading of it in relation to 19th century sailors, and I wouldn’t be surprised if it were recognized for centuries prior to then.

[Roadfood]

I appreciate the response, but it doesn’t really answer my question. I know that the notion of sea legs and land legs goes way back, but what is the mechanism – physiological or pyschological or otherwise – that causes the profoundly realistic sensations of motion to persist for days? “Sea legs” and “land legs” were some of the things I tried searching the web for, and I didn’t find anything useful.

[rowrrbazzle]

I think it’s analgous to the “waterfall illusion” http://unisci.com/stories/20014/1011012.htm :

The researchers then show that the illusion is caused by the adaptation of some neurons following repeated stimulation. As we watch the water fall downward, the neurons that are selective for downward direction adapt and become less responsive. When we then look at the static rock, the upward-selective neurons will be relatively more active, leading us to perceive that the rocks are moving upward.

The longer you’re exposed to the stimulus, the longer the reverse effect will take to fade.

[rowrrbazzle]

Also known as motion after-effect http://www2.fhs.usyd.edu.au/ess/odwyer/motorcontrol/Posture/Posture.htm :

Figure 9 (from: Kandel et al 2000, p. 822):
A. Subjects walk with eyes open on the rotating circular disc for 1-2 hours. Throughout this period the space-stationary trunk is associated with a constant angular velocity relative to the stance foot, since the foot rotates with the turntable when planted on it. After adaptation, the subject unknowingly walks in a circular path on firm ground by steadily rotating the trunk relative to the stance foot (B), but can readily propel a wheelchair straight ahead with the hands ©.

The ‘after-effect’ observed following the imposed activity in this study is analogous to the type of adaptation that occurs after spending several hours on a boat - the so-called ‘sea-legs’ of the sailor.

[Gary_T]

Go to Google and enter <“sea legs” land balance inner ear>. A number of the entries get into medical explanation, and may have what you want. It seems clear to me that it is physiological rather than psychological.

[micco]

I think the physiological term is accommodation. At least in visual effects, accommodation is the cause of motion after-effects and the waterfall illusion that rowrrbazzle mentions. Anytime you adjust to current stimuli, whether it’s a constant visual effect or moving ship deck, the adjustment is called accommodation and will persist for a while after the stimuli are changed.

[One_And_Only_Wanderers]

*Originally posted by Roadfood *
**I appreciate the response, but it doesn’t really answer my question. I know that the notion of sea legs and land legs goes way back, but what is the mechanism – physiological or pyschological or otherwise – that causes the profoundly realistic sensations of motion to persist for days? “Sea legs” and “land legs” were some of the things I tried searching the web for, and I didn’t find anything useful. **

Insert standard IANA “whatever the hell an expert in this field would be caused”

Logically.

Act 1 you board the ship. Your previously sedate inner ear fluids are now having to cope with rocking, swells, all sortsa boat related stuff

Result you feel queazy.

Act 2 your brain gets used to the ‘swirly’ signals it’s getting from the inner ear and indeed grows to expect them

Result, hey I may survive this cruise after all

Act 3 Cruise ends, you disembark, you inner ear fluids return to being sedate. Uh oh your brain is now expecting swirly signals

Result you feel queazy again

Act 4 (hopefully) your brain readjusts to sedate inner ear signals.
Does this sound like a reasonable hypothesis??

[Roadfood]

Thanks rowrrbazzle, Gary T, micco, and Carl_A_Norris, that’s exactly what I was looking for.