Pulfrich effect

[P3D Gabriel Jacob <jacob@xxxxxxxxxxxxxx>]

Note: This was posted a few days ago but did not reach the digest so 
I am reposting it.

>Dr. George A. Themelis writes
>Pulfrich Pendulum effect
>
>
>From R. L. Gregory's "Eye and Brain -- The Phychology of
>Seeing", Third edition, p. 83:
>
>It will be found that the bob does not appear to swing in a
>straight arc, but to describe an ellipse...

>Now, what causes this strange effect?  By reducing the light,
>the dark glass delays signals from this eye... This gives an
>effective horizontal shift of the moving image... generating
>stereo depth.  For the brain it is as though the bob is
>swinging elliptically."
 
Just like to add something to the above explanation since this is 
technically correct month! While the above explanation "By reducing
the light, the dark glass delays signals from this eye" is true to
the extent in that is what it achieves, one might conclude that the
dark glass actually retards the light to the eye enough to see two 
different frames and thus 3d. This is not true! Other books have 
erroneously been more explicit and state that this as the reason.
The dark lens does slow down the light but this is a insignificant 
amount of time. Not enough to delay one frame which is roughly in 
milliseconds. The dark lens (or even a piece of clear glass) will
retard the light down but not significantly to observe the pulfrich
effect. What actually does it, stated quite simply (from Entertaining
Science Experiments with Everyday Objects.) is that the illusion
arises from the fact that darkened retinal images are more slowly
transmitted to the brain than bright images.
This is furhter supported by the following statement in the original
post. 
>Other implications manifestations of this delay:
>
>- "Comet's tail" in moving fireworks.
>- Lengthening of reaction-time when driving under dim light
The above does not state anything about glasses but only that that dim
light will lengthen reaction-time which is correct.

By the way, since we are discussing the Pulfrich effect, there was an 
old computer IBM PC game late 80's early 90's called Beyond the Black
Hole that utilized the pulfriched effect. It was a simplistic game
,with space ships flying around back and forth on the screen.I think
you had to shoot them down or something. The graphics looked like 2D
cutouts but when you put the glasses on they seemed to receed and 
then come out of the screen, similiar to the pendulum effect. The 
3d was effective but like I said it was simple graphics. I still
have the game buried somewhere. 

I think everybody on this group should at least try experiencing the
effect like others have stated, with one lensed sunglasses and your 
television set because the 3d effect is very real and sometimes startling.

Lastly I'd like to inform everybody I have a bunch of Pulfrich eye
glasses with two dimming lenses that results in 6D.
I will let them go for only slightly more than the 1 dimming lense
the competitors sell. If interested just send a check to.

6D Just Kidding Rd
PulfRICH, OK

On a different note, I noticed that some posts are replied to in the
same digest. How is this possible. Is there another way of getting 
this digest on the net or is the digest different for different places.

Gabriel Jacob
jacob@xxxxxxxxxxxxxx  


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