Re: Pulfrich Take 2

[P3D Jim Crowell <crowell@xxxxxxxxxxxxxxx>]

At 10:25 AM -0700 6/13/97, P3D Scott Langill wrote:
>
>The common perceptual reference for disparity would involve non-
>corresponding spatial points on the left and right retina. The
>Pulfrich Effect is dependent upon the slower transmission and processing
>of neural signals from the rod receptors in the dark adapted eye (the
>eye with the darkened lens covering it) versus the signals from the cone
>receptors in the eye which is not dark adapted.

Your typical pulfrich filter isn't nearly dark enough to push you down into
the scotopic (rod-dominated) range; under normal conditions, it's all done
with cones, I'm pretty sure.

-Jim C.

>
>> Perhaps you mean that depth cues from *focus* (accommodation) are
>> functional out to about 20 feet? Unless you have really bad depth
>> perception, you should be able to see depth (without motion) much
>> further out than that. Also, humans *do* automatically move their
>> heads to get parallax to judge the distance of very distant objects.
>> And Pulfrich works in real-world applications - I experimented with it
>> about 5-6 years ago looking out of car and airplane windows, and
>> others have also done this. The brain already uses the relative
>> motion to reconstruct depth - the Pulfrich effect allows another part
>> of the brain to pitch in and reinforce the depth perception.
>
>My understanding of experimental evidence is that given the limitations
>of stereoscopic acuity, most individuals make judgements relying
>upon two dimensional cues when viewing distant objects.

Sure, the usefulness of stereo relative to other cues falls off with
viewing distance.  How far out you think stereo is useful depends on how
fine a depth interval you want to be able to use it to detect...

BTW, depth cues other than stereo are properly referred to as "monocular",
not "two-dimensional".

-Jim C.

----------------------
Jim Crowell
Caltech Division of Biology
216-76
Pasadena, CA
Tel: (818) 395-8337
Fax: (818) 795-2397
jim@xxxxxxxxxxxxxxx



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