stupid question

[michael]

What gives some rims more of an appearance than others the effect of spinning backwards when going forward at certain speeds?

Good Question...

Propellers give the same effect, hence the BMW symbol.

[lee]

It's a subject that has generated several scientific papers, all of which basically end up saying they don't know how to explain an optical illusion's process in our heads.

What seems to be widely accepted is that the effect is only seen (a) in movies (frame rate issues with perception) or, (b) with a spinning object that introduces a strobe or frame like effect to our vision, i.e., the wheel or propeller has to have openings - if either were solid the effect wouldn't be seen.

[CigarJohnny]

Originally posted by lee
It's a subject that has generated several scientific papers, all of which basically end up saying they don't know how to explain an optical illusion's process in out heads.

what seemed to be widely accepted is that the effect is only seen in movies (frame rate issues with perception) or with a spinning object that introduces a strobe like effect to our vision, i.e., the wheel or propeller has to have openings - if either were solid the effect wouldn't be seen.

The movie issue is easy to understand as it is merely an issue of recording frame rate and the RPM of the spinning object. Same as when recording a computer or TV screen. You usually see a scrolling effect on the recording as you capture the frame refreshes on film.

I do not believe that the human brain sees a "refreshless" view of the world. We process visual input at a certain frame rate as well. That is why we see this reverse spinning in real life as well under ideal conditions. One of the most convincing demonstrations of this was seen by me as I walked one evening. I was carrying a walking stick and was twirling it as I walked. Instead of seeing it as a smooth motion it actually appeared to be a stepped motion not unlike a strobe effect. It was quite intriguing.

Johnny

[ensteele]

I saw a similar affect when someone was throwing beer bottles at me when I was running from a big dog across the lawn near a park with lights that were on a tall pole with fog covers on them. As I tripped and rolled down the grassy hill and into the bramble bushes, I looked up as I hit a tall but slender tree and they looked like they were spinning backwards as they just missed my head. It was quite intriguing too.

The stick and the bottle illusions were likely a result of the frequency of the lighting. Wave your hand in front of a CRT, then go outside and try it in sunlight. You see a smooth motion outside because the sun isn't pulsing at a few dozen Hz...

[n00b on demand]

Originally posted by ensteele
I saw a similar affect when someone was throwing beer bottles at me when I was running from a big dog across the lawn near a park with lights that were on a tall pole with fog covers on them. As I tripped and rolled down the grassy hill and into the bramble bushes, I looked up as I hit a tall but slender tree and they looked like they were spinning backwards as they just missed my head. It was quite intriguing too.

LMAO im sorry earl i laughed really hard when i read that!!!

[michael]

Wow did this not go the way I expected! Sorry I took so long to check back in. I was wondering what characteristics of a rim intensified this effect.
I was refering to the thickness, quantity, length, shape and finish of a rims spokes.

[lee]

Originally posted by michael
Wow did this not go the way I expected! Sorry I took so long to check back in. I was wondering what characteristics of a rim intensified this effect.
I was refering to the thickness, quantity, length, shape and finish of a rims spokes.

does any thread?

the effect varies from person to person, and would be maximized by whatever helped induce a strobing effect. I would guess that would be somewhere around 1/2 of the space filled, straight sections (vice curved like on the SVX), not too many spokes (say 4-6), and probably as bright a finish as possible (viewing is assumed to be typical, i.e., underside of car dark). I'm basing this SWAG on seeing solid steel wheels painted in quadrants of alternate white/black.

[Hocrest]

Originally posted by michael
I was wondering what characteristics of a rim intensified this effect.

Just go on down to Wally world and get a set of those spinner hubcaps

[michael]

or the chrome skull and cross-bones with the red plastic jem eyes!

[CigarJohnny]

Originally posted by Hocrest


Just go on down to Wally world and get a set of those spinner hubcaps

I sense that the next big thing in wheels would a variation of the spinner effect where in the free spinning piece would instead be geared somehow to appear to not be spinning as the wheel rotated. I think that would be an even wilder illusion that a wheel spinning while standing still. What do you think?

Johnny

Some guys have already attached weights to one side of their spinners, so that they remain mostly stationary as the rest of the wheel spins...

[CigarJohnny]

Originally posted by ThetaReactor
Some guys have already attached weights to one side of their spinners, so that they remain mostly stationary as the rest of the wheel spins...

That is an even simpler yet better idea than mine. That way it is still no matter what RPM the wheel is turning. I think that would look way freakier to see a car "Sliding" down the road than it is to see one moving while standing still.

Johnny

Well, this is an interesting thread. I think that I may be able to explain this phenomena, and the processes of your vision.

When you stare directly at an object (like a CRT), the "refresh rate" of your vision is approximately 72Hz. When you move your vision to the side of an object, but keep it in your peripheral vision, the "refresh rate" is approximately 80 - 85Hz. This is why a high quality CRT monitor, with a refresh rate of 80Hz or more, is very expensive. Lower quality CRT monitors, that stay around 72 - 75Hz are adequate when you look directly at them. But if you move the monitor to the very edge of your vision, the refresh rate becomes quite apparent. Anything below 70Hz will be visible when looking right at it, and will likely give you headaches and damage your vision.

This variance in rates is likely because your direct vision sees in color, while the very edge of your vision sees in black and white. More on this later, though.

I could most certainly be wrong, but here is my theory on why wheels/spokes appears to spin backwards at high speeds. It will greatly help if you try to still imagine a car driving at freeway speeds, but slow down your visualization of the spokes into a frame-by-frame sequence. I think that they seem to spin backwards because the spokes are spinning a rate slightly faster than the "refresh rate" of your vision. In "frame 1," your brain simply sees the wheel for the first time. Each subsequent frame is compared to the first. So, when the spokes are in a location just before their location in the first frame, it makes it seem as though the wheel is spinning backwards. This is also why they seem to spin backwards very slowly, despite the fact that the car is moving very quickly.

This is the same thing as when you videotape a CRT monitor. With the right camera, and the right monitor, the refresh lines seem to scan upwards. This is not correct, because CRTs scan downwards. This makes me believe that it is not an optical illusion created by your brain, just a difference in the refresh rates. A camera does not have a brain, or at least one capable of fabricating optical illusions.

I quickly made and attached a JPEG of this process. One part of the wheel in the picture is filled in with gray, to show the direction of rotation of the wheel. The other part is colored in red, to illustrate my statements in the previous paragraph (the location of the spokes being just prior to the previous thread, despite the wheel moving forward). Hope this helps.

About the color and black and white stuff... It seems tough to believe, and when I first learned this, I didn't believe it either. You look at the stack of neon green post-it notes on your desk, and then look away from them, and think, "Those are green. I can see that they are green from the edge of my vision."

No, you can't. Your mind remembers that they are green. Try this: Get an assortment of color markers (five or six colors, I prefer Sharpies), and look at them all. Try to remember all the colors. Now, have someone very slowly move the edge of a random marker into your field of vision. Tell them to stop just as you can see the very edge of the marker. Now, tell them what color it is.

Believe me now?

Anyway, on with the shouting and yelling. I always seem to bring it to every thread I post in.