P3D pulfrich historically

[abram klooswyk <abram.klooswyk@xxxxxx>]

Early this year postings by Larry Berlin, John Roberts and Gabriel
Jacob contained some historical errors on Carl Pulfrich and his effect. 
There is much literature on the subject. A summary is in: 
Susan Christianson and H.W. Hofstetter "Some historical notes on Carl 
Pulfrich", American Journal of Optometry 1972, vol 570 pp 944-947.  

Even shorter:
Carl Pulfrich (1858-1927) was a german physicist who developed the 
Stereo-Comparator, a device to take measurements in stereophoto's, it 
was invaluable in cartography. He was employed by Carl Zeiss, Jena, who 
marketed the apparatus.  
Pulfrich published many papers on his stereoscopic research, but he lost 
vision in his left eye, apparently in 1905 or 1906.  

Max Wolf in a 1920 publication noticed a disturbing stereo effect when 
moving plates in the Stereo-Comparator. Pulfrich found out that some 
others had observed it earlier.  
Zeiss employee F. Fertsch found that the effect was due to difference in 
brightness of the two views, and also suggested the explanation of the 
effect by difference in perceptual latency of the eyes. Pulfrich's son 
Hans did the theoretical analysis of the apparent movement.  

Carl Pulfrich designed experiments to investigate the effect, and added
an application of it, all published in a series of articles: 
"Die Stereoskopie im Dienst der isochromen und heterochromen 
Photometrie", Die Naturwissenschaften 1922 vol 10 pp 553-564, 569-574, 
596-601, 714-722, 735-743.  

Pulfrich gave full credit to all mentioned persons and wrote: 
"I have never been able to observe these effects myself, for I have been 
blind in the left eye for 16 years" (translated from German).  
Historically speaking of the "Wolf-Fertsch-Pulfrich" effect would be
justified, but "Pulfrich effect" is the accepted name. 
(Compare: in German and some other languages X-rays are 
called "Roentgen rays", against Roentgen's own wish.)

The Pulfrich effect is still an issue in vision research up till now.  
MedLine, an international index on medical literature (also on the Web) 
gives about 75 scientific articles in the last 30 years on the keyword 
"Pulfrich" (in title or abstract), most published in ophthalmological or 
physiological journals. Recently a paper on baseball hitting with 
Pulfrich effects was published.  

I have written on "A Pulfrich 3-D History" in Stereo World jan/feb 1989 
vol 15 Nr 6 pp 14,15 and 27, discussing the stereoscopic snow storm on 
empty TV channels (unfortunately now on most sets replaced by uniform
blue), and early Pulfrich animation movie. I also described "Pulfrich 
free viewing" (not earlier described to my knowledge): squeeze one eye 
a little and use the eyelashes as filter. This is a poor method but 
illustrates the principle. Another easy "filter" is a pinhole: 
just make a tiny hole in a piece of card and hold it close to one eye.  

Please don't speak of a "Pulfrich effect with two eyes" when not 
perceptual delay between the eyes is meant, but delay between hand 
movements and visual perception. Terms already are confusing enough.  
Rather give that effect your own name.:-) 

Abram Klooswyk
(abram.klooswyk@xxxxxx)


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