Pulfrich Pendulum effect

[P3D Dr. George A. Themelis <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

>From R. L. Gregory's "Eye and Brain -- The Phychology of
Seeing", Third edition, p. 83:

"Not least remarkable about (the Plufrich Pendulum effect) is
its discovery, for this phenomenon cannot be seen without
two functional eyes, and yet its discoverer was blind in one
eye!  The experiment is worth trying out.  Take a length of
string, and a weight for a bob to make a pendulum about one
metre long.  Swing the pendulum in a straight arc normal to
the line of sight.  View the oscillating bob with both eyes,
but cover one with a dark... glass such as one filter of a
pair of sun glasses.

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 singals 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."

Other implications manifestations of this delay:

- "Comet's tail" in moving fireworks.
- Lengthening of reaction-time when driving under dim light
  and deficulty in locating moving objects precisely.


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