Re: Pulfrich Take 2

[P3D Larry Berlin <lberlin@xxxxxxxxx>]

>Date: Fri, 13 Jun 1997
>From: P3D Scott Langill comments:
>
>My  earlier posting "Discounting the joy of Pulfrich 3D" engendered a
>number of interesting responses..........
>..... Much of the confusion seems to stem from my connotative use of the
>word illusion.
>.........................
>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) ............

******  Someone else commented in a recent digest that the dark pulfrich
lens isn't sufficient to make the eye go into that much of a dark adapted
state. Pulfrich disparity takes place largely during mental processing.
Brighter, stronger signals get the most direct acknowledgment in the visual
processing center. A kind of prioritizing. While there may be physical
factors in the eye that contribute to a delayed signal, it isn't the full
source of the observed disparity. There is a whole chain of events involved,
the sum total of which provides the effect. What counts to our perception is
the relatively final stage of this process where remembered data is replaced
with what is considered to be new information indicative of motion. Pulfrich
disparity is primarily created during this automatic
decision-making/signal-priority process.

>........................... Usually a stereophotograph (depending on
>viewing distance and assuming it is not hyperstereo, etc.) portrays an
>accurate representation of the reality of the subject. This is not the
>case with the Pulfrich Effect except under extremely controlled
>circumstances where the constraints placed on a filmmaker or
>videographer arguably would totally disrupt the storytelling function. 

******  I have to take issue with this conclusion. There is no driving need
that a video or film portraying a pulfrich effect needs to show accurate
real-life depth. The effect isn't of that nature, and isn't used strictly
for something it can't accomplish. It is used for a very real depth effect
which protrays varying degrees and types of correlation to physical reality.
In the sense that it differs from reality it can be used as interpretive
symbol which extends the language of expression. This is a gem for
storytellers if they will visualize this language in their story. The NBC
show did an admirable job in the use of surrealism and dream to twist and
experiment with the effect. What they didn't do, which could have been done,
was to maintain a manifestation of these effects for a much higher
percentage of the total time. It is even possible, in the scheme of things
to maintain such an effect on a 100% level without undue complication, if
the story and camera are choreographed carefully. Especially so if the whole
presentation makes alternate use of a lens over either eye.

It is a form of dance in itself. A dance within the mind, interactive with
the relativistic dance before our eyes. As such it has the utmost viability
as an art form. There is nothing second rate about it. It exists as a
repeatable effect for humans and we as a species are learning how to move in
this new dance. 


>In a car chase across the screen where one vehicle is outpacing the
>other, either the faster vehicle looks unrealistically wide or the
>slower vehicle looks unrealistically narrow.

******  I have not observed that such is the case. Relative motion on screen
doesn't appear to change the size or shape of the objects themselves, just
their spatial location.

>................................... An extreme example of the brain's power
to do
>this is the inability of most people to see human faces as hollow when
>viewed with prisms reversing disparity.

******  This so called *inability* is nothing more than unfamiliarity,
except in isolated and rare cases. Such a measure cannot be taken as an
accurate indication of whether people in general have the ability to be
perceive the hollow face. With training and practice, the same sample group
used in the first case would likely approach the 100% ability point. The
cues are there waiting to be perceived, but the average person is not used
to recognizing or using them. The above referenced *brain's power* is
actually a case of unused power, a stumbling due to unused abilities.


>..........................You Quoted:
>........... the April 1974 edition of American Cinematographer entitled
>"The Video West, Inc. Three Dimensional Photographic System"...........
>.....................Pulfrich is the perhaps the
>cheapest game in town. The question is,hHas the disservice done to the
>public's 3D enthusiasm by the headaches of poorly made 50s anaglyphic
>films been replaced by the pseudoscopic effects of the 90s Pulfrich
>television shows?

******  It's obvious the article's author doesn't have all the facts and
hasn't understood what Pulfrich offers. Pulfrich is elegant in it's
simplicity and not to be discredited for that simplicity. It may be abused
in it's application, but it still has potential for anyone wishing to use
it. It's likely that many who use it won't understand it.

>.........................
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>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. 

******  So much for common misconceptions. The human mind is capable of
absorbing a range of visual data and assembling it into a larger whole than
is visible to the eyes at any given moment. By this means you can walk along
side the Grand Canyon and develop an acute awareness of depth factors on the
other side which are certainly greater than the two dimensional cues you
mention and more extensive than what is visible in a given single spot. Yes,
such clues are a part of the process, but not all of it by a long ways.

>The issue is
>whether the Pulfrich Effect provides realistic information or an
>accurate portrayal of the true depth of objects. ........

*****  Why is that an issue  Pulfrich isn't that way as a rule by
definition. Why expect it to be something it's not? Compare it to reality,
yes but expect accurate portrayal, I think not. It's a matter of expectation.

>.................
>The issue is whether you can tell an effective story or present an
>effective story with all the constraints that compensating for the
>misrepresentational effects of movement with the Pulfrich Effect. I
>doubt whether they are aiming for an accurate representation of depth, I
>think "a jazzy effect, with occasional pronounced depth effects" sounds
>more Hollywood probable to me.

*******  Consider the dance. Is the dancer misrepresenting reality when she
is facing away from us? Or holding her leg high, or spinning around? Is the
dancer feeling *constrained* by gravity or using it to advantage?

>.................................. The point is, I
>disagree that it is a "useful perception of depth". The television
>presenters would have me believe that this is an accurate portrayal of
>the depth relationships of the objects and backgrounds filmed, in fact
>it is not. 

********  It wasn't invented as an accurate portrayal. They (the producers)
didn't claim that it was. I don't expect it to be.

>I enjoy the Pulfrich effect to the extent it shows me how I
>can be fooled into thinking things are happening which in fact are not
>happening 

*******  Any media you observe on TV or a computer monitor qualifies for
your definition of *not happening*. You are daily fooled into thinking
persons are in front of you talking and living their lives in your living
room. You know that isn't really happening but don't castigate them for that
bit of technical illusion. If Pulfrich can add to the enjoyment of that
media, it makes more sense to use it than not.

>(something which is moving in a straight line looks like its
>moving in a circle.  In the Ames rotating trapezoidal window illusion an
>object attached to one side will appear to orbit the entire window. If I
>place an object in front of the pendulum moving in a straight arc, the
>Pulfrich Effect makes it look like its orbiting the object. Both could
>be termed pseudoscopic effects. Pretty neat, but are these accurate
>portrayals of the objects. No. A funhouse mirror is entertaining, but
>should I promote it as how things really look?

*******  The waters of a quiet lake look pretty flat, but in reality they
form a curved surface. Which is reality, your perception in the moment of
flatness, or the larger reality of curvature? I propose both are a part of
reality.

>...........................
>I agree to the extent that I believe that the requisite attention to
>motion is a crippling artifact of utilizing the Pulfrich Effect in
>television and film presentations.

******  I believe several scenes in the NBC show could have extended the
camera motion a lot, without any crippling effect to the intent or
expression of the script. Dancers don't consider their motion to be a
crippling artifact of human expression. The Pulfrich effect takes place in
the presence of motion. Therefore anything intentionally using that effect
will be made by featuring motion. That isn't a crippling factor.

>..................

I've enjoyed all the discussions on this thread!

Thanks

Larry Berlin

Email: lberlin@xxxxxxxxx
http://www.sonic.net/~lberlin/
http://3dzine.simplenet.com/


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