Re: Wagon-wheel illusion again

[Donald McBurney]

Now that we are all congratulating ourselves on figuring out 
stroboscopic motion with steady illumination, let me throw a monkey 
wrench into the discussion.  Could it be the result of torsional 
nystagmus, which is (I think) rotation around the line of sight?  There 
is abnormal torsional nystagmus (and a Google search turned up tons of 
stuff), but it runs in my  mind that there is a normal torsional 
nystagmus that would tend to keep a rotating object (such as a wheel) 
stable on the retina (analogous to vestibular nystagmus in the 
horizontal plane). 
   don
   Donald McBurney
As usual, I don't have time to research this, but maybe Stephen does.  ;-)

Ken Steele wrote:

Tom: Congratulations!

Tom Allaway wrote:

To all, but especially Stephen, Doug and David:

    I do believe I've got it!  The demonstration experiment involved, in
my case, a small kitchen device similar to a salad spinner, containing a
rotating perforated plastic tub.  When spun under a flourescent light,
it showed a clear "wagon wheel effect" (i.e., the temporary appearance
and reverse rotation of the perforations during deceleration).  I took
it outside, and there was no effect to be observed.  The crucial test:
with my only source being daylight, I applied to my skull a vibratory
stimulus, in the form of the business end of an electric toothbrush
(minus the brush part) pressed against my chin.  Violets!  There was the
wagon wheel effect!
Q.E.D.
Let's hear it for empiricism.




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