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paulsinnerchild
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15 Dec 2006, 11:28 pm

When I was a kid I frequently amused myself spinning around in circles in the room and when I stopped to room just seemed to keep revolving. I felt a bit dizzy and nausious after it all but I just loved doing it. I felt like I was on a boat ferry being tossed around in a storm. Kind of a bit like you seen on Cape Fear. Can anyone here have any explanation for this illusion of motion


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Fraya
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15 Dec 2006, 11:34 pm

Its the motion aftereffect also called the "waterfall effect"

The brain has separate motion detectors for different directions of motion. The motion detectors produce a stronger signal when there is motion and a weaker (but non-zero) signal when there is no motion. As long as all the motion-detectors are in balance with each other, you do not perceive any motion. When strongly stimulated by motion in a particular direction, the subset of motion detectors that respond to that motion become fatigued. When the stimulus is removed, the motion detectors for the opposite direction produce a stronger signal for a few seconds, until the fatigued motion detectors recover.


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logitechdog
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15 Dec 2006, 11:49 pm

this will help you get into it again probably

http://chiron.valdosta.edu/mawhatley/2500/spiral.htm



AV-geek
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16 Dec 2006, 12:14 am

The thing I have always wondered is how the brain responds to weightlessness, and what the effect you experience is. Because there is no gravity, I imagine your body looses it's sense of what direction "down" is and really confuses things. Think of it this way, you can stand on your head, lay on your side, or any other position for that matter, and you will always know where down is. Now, think of that ride at the fair that spins you around really fast. I notice when I ride it that once it gets up to full speed, it feels as if it's turning vertical, and I'm laying on my back at the bottom of the drum parallel to the ground, not standing up against the side of the drum perpendicular to the ground, like I actually am. The reason is because the inertial forces of the spinning ride has changed the gravity vector. Instead of gravity pulling down at my feet, it's now pulling my body against the wall...so now I percieve "down" as being in the direction of the force, which is behind my back, not below my feet.

Now, how does this work in weightlessness??? Since there's no gravity, there's no "down" reference. I would think that the perception of motion in a weightless environment, like riding in the space shuttle, would be one of my body standing still, and everything else rotating around me if I were to spin myself while floating weightless.



logitechdog
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16 Dec 2006, 12:46 am

How Astronauts Feel in Mircogravity

Astronauts have the following feelings when they first encounter microgravity:
- Nausea
- Disorientation
- Headache
- Loss of appetite
- Congestion

The longer they stay in microgravity, the more their muscles and bones weaken. These feelings are caused by changes in various systems of the body. Let's discuss how the body responds to microgravity.

Spacesick
Before dicussing spacesick, let's talk about how people sense position and motion. Orientation and motion are sensed by using the vestibular system, which is located in the upper portion of the inner ear.
How the vestibular system senses orientation with respect to gravity?
- It has otolithic organs that contain crystals of calcium carbonate
- The crystals are attached to hair-like sensory nerve cells in three orientations (x-, y-, z-axes)
1. When you bend your head in different directions (forward, backward, sideways), gravity pulls on the crystals that are oriented in the direction of the pull.
2. The affected crystals stimulate the attached hair cells to send nerve impulses to the brain.
3. The brain interprets these signals to find out which way the head is oriented in space.
How the vestibular system sense motion?
- There are three semicircular canals for sensing motion, specifically acceleration.
- They are oriented at right angles to one another, and each is in one of the three directions (x-, y- or z-axis).
- They contain fluid called endolymph and hair-like sensory nerve cells.
1. As your head accelerates in a given direction, the endolymph lags behind because of its initial resistance to change in motion (inertia).
2. The lagging endolymph stimulates the appropriate hair cells to send nerve signals to the brain.
3. The brain interprets them to find out which way the head has moved.
The nausea and disorientation that you feel are like your experience in a drop on a roller coaster ride, only you have that feeling constantly for several days.
This is the feeling of space sickness, or space motion sickness, which is caused by conflicting information that your brain receives from the eyes and the vestibular organs located in the inner ear. The eyes can see which way is up and down inside the shuttle. However, because The vestibular system relies on the downward pull of gravity to tell the astronauts which way is up versus down and in which direction they are moving, it does not function in microgravity. So the eyes may tell your brain that they are upside-down, but the brain does not receive any interpretable input from the vestibular organs. Their confused brain produces the nausea and disorientation, which in turn may lead to vomiting and loss of appetite. Fortunately, after a few days, the brain adapts to the situation by relying solely on the visual inputs, and they begin to feel better. And NASA has produced medication patches to help astronauts deal with the nausea until their bodies adapt.
Puffy Face
Normally, when someone standing upright, gravity pulls blood downward so it pools in the veins of the legs. In microgravity, the blood shifts from the legs into the chest and head, so the face will feel full and the sinuses will feel congested, which may lead to headaches and space motion sickness. Also, the face tends to get puffy and the sinuse swell. When the blood shifts to the chest, the heart increases in size and pumps more blood with each beat. The kidneys respond to this increased blood flow by producing more urine. Moreover, the increase in blood and fluid decease anti-diuretic hormone (ADH) secretion by the pituitary gland, which makes people less thirsty. Therfore, astronauts do not drink as much water as they might on the Earth. After returning to the Earth, gravity will pull those fluid back down to the legs and away from the head, which will cause the people to feel faint when standing up. But the astronauts will also begin to drink more, and the fluid levels will return to normal in a couple of days.

Edit2:- starts changing it to make it look like I typed it :p lol



Last edited by logitechdog on 16 Dec 2006, 12:53 am, edited 1 time in total.

Fraya
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16 Dec 2006, 12:47 am

The perception of motion is mostly visual.

In a weightless environment the motion aftereffect works normally.

However you do have to deal with space adaptation syndrom which is the bodys response to the inner ear (the organ that tells you which way is up, maintains your balance and helps you detect bodily motion) going haywire.

The symptoms include nausea, vomiting, vertigo, headaches and lethargy it generally lasts 2 to 4 days and is very unpleasant.

Its one of the things astronauts are trained for (and a factor in determining who is unfit for space travel) with simulated microgravity. Since in a weightless environment down is whichever way you perceive it to be it can change drastically and quite randomly resulting in permanent vertigo. However a small percentage of the population are able to to maintain a constant mental orientation regardless of a lack of gravitational reference or even more rarely a select few are capable of functioning completely without a sense of orientation.

[edit] Blah Logi beat me to it but I didnt cut and paste my response so nya :P


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One pill makes you larger
And one pill makes you small
And the ones that mother gives you
Don't do anything at all
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paulsinnerchild
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16 Dec 2006, 4:55 am

Thanks for that, I have allways been mysified by that ever since I was a kid. I wonder what would happen to you if that part of the brain which process motion was damaged in some way. Would you be seeing a lot of jerky still images or something?