T3D Re: Perspective on extreme 3d

[abram klooswyk <abram.klooswyk@xxxxxx>]

John Toeppen wrote (03 Jun 1999 , T3d Digest 498):
>Accommodation may account for the perceptual problem with extreme 
>depth disparity in an image.  Our eyes attempt to refocus for 
>different convergences.  We are familiar with interpreting an 
>image in a 2D plane as though it were 3D.  Perhaps we try to 
>refocus when we see stereo in the extreme.

I agree with John Bercovitz (T3d Digest 499) that it is not 
clear how
>people who have lost their accommodation fit into this theory.

Everybody will like to loose accommodation some time, 
because it means that you live long enough to get there.
But the pupil diameter of older people is also significant
smaller than of children, which gives some compensation
by the greater depth of field.

In a thread called "A Third Simple One" Bruce Springsteen,
Tom Deering, Greg Wageman and others discussed a similar
issue (September 1998, T3d Digests 367 - 370), and
John Bercovitz said:
>(...) If my eyes are put in a position where they must try to 
>accommodate, I feel the strain of the attempt (...)

This indeed does no longer hold when accommodation has gone.
And accommodation IS for providing sharp images, the main 
cue for accommodation change is blur. Since accommodation no
longer follows convergence in the elderly, they get no blur
and no conflict between convergence and accommodation.

In T3d 370 I said:
"If eyestrain (in stereo viewing) in young people results from two 
conflicting 'forces' on accommodation:
1. convergence-induced accommodation (although the link is not so tight
   as some people believe), leading to blur in stereo viewing,
2. blur-driven accommodation (the main 'force' on accommodation), which
   restores definition,
then obviously the latter is absent in the elderly, if they wear the
right glasses or adjust the viewer properly. 

But, when the accommodation muscles go on following convergence in the 
elderly, there is nothing wrong: this is normal in natural vision! But 
in *them* it does *not* lead to blur, as it would do in the younger, 
so no conflict arises, so no eyestrain." 

Or does John Toeppen now suggest that the *absence* of blur is
the problem? I like paradoxes!

Abram Klooswyk


------------------------------

End of TECH-3D Digest 500
*************************