Re: [photo-3d] Re: 3d vision again

["John A. Rupkalvis" <stereoscope@xxxxxxxxxxxxx>]

When first reading your comments, I tended to agree.   But, on further
reflection, I don't think that to "try it out regardless" is that bad an
idea.

However, she should be advised that if she finds this experiment
uncomfortable, she should not feel obligated to continue.  Every visual
experience is part physiological and part psychological, and this is true
for all of us, no matter how good our natural visual mechanism happens to
be.

She may find that she would prefer not to try this "on the spot", but rather
at some other time when she is more in a frame of mind to experiment.

This advice should apply to all of us, even for learning to freeview, or
view with mirrors, or any other visual activity for which we are not already
accustomed.

The best time for any of these things is when "we, ourselves" really want to
do it.  That is when we are most likely to be successful.

I have had people tell me that learning to freeview by either method was
"impossible".  Then, they called me the next day to tell me it worked for
them the first time they tried it alone.

JR

----- Original Message -----
From: "Abram Klooswyk" <abram.klooswyk@xxxxxx>
To: <photo-3d@xxxxxxxxxxx>
Sent: Monday, October 09, 2000 2:54 PM
Subject: [photo-3d] Re: 3d vision again


> Rogers  [ka2hsu] wrote 7 Oct 2000 on his daughter's
> stereoviewings problems.
>
> > (...) she has never been able to obtain enough muscular
> >control of the affected eyeball to enable her to bring her
> >eyes to focus simultaneously on an object.
>
> However, as Lynda Nygren and Jim Crowell have indicated
> (more or less), fusion is required even before stereopsis
> eventually can arise.
> Ophthalmologists and optometrists, and most opticians
> (depending on national rules) have tests, not only for
> stereopsis, but also for testing fusion.
>
> The classical test for the latter is the Maddox cross. In a
> dark room a small luminous disk is shown, and the subject
> wears glasses with cylindrical rods in it, at the left
> horizontally and at the right vertically orientated, and
> mostly colored red, to prevent prismatic dispersion.
> A person with binocular vision, although not necessarily
> having stereopsis, will see a luminous cross (the cylinders
> spread the disk's light  to a bar). But persons with a "lazy
> eye" (amblyopia) typically see only one bar, suppressing the
> other. There are several types of amblyopia.
>
> Rogers said that his daughter has an acuity of 20/20
> in both eyes (one after correction). This is not typical
> of amblyopia, where the lazy eye tends to have a
> lower acuity. But she might have alternating suppression,
> using both eyes, but one at the time, so again no fusion
> failing on the Maddox test, and no stereopsis.
>
> Another test, which also can be tried at home, is with
> afterimages. In a dark room, let a person look with one eye at
> a vertical neon light bar. Then immediately after with the
> other eye at the light bar, but rotated  horizontally.
> Next let him/her close both eyes and report what they
> see. With binocular vision again the afterimages will
> form a cross.
> (Wheatstone did this afterimage test with _stereo_
> drawings, an early proof that stereopsis depended
> on retinal images, and not on changing of convergence.)
>
> Since Rogers' daughter had the eye muscle condition from
> birth, it seems unlikely that she can acquire stereopsis now.
> My references indicate that eye muscle correction
> must be before the age of 3 years in these cases. (Jim has
> given the figure of 5-7 years, but I believe that applies
> only for children who have had stereopsis as babies or as
> infants, but developed strabismus at about 3 years of age.)
>
> I'm sorry to disagree with Linda that Rogers' daughter
> should "try it out regardless".
> There are conditions in which fusion and stereopsis are
> _impossible_, and there are reliable tests to establish
> whether such a condition exists. It is very discouraging to
> spend efforts on an impossible task, and it might even harm
> father-daughter relationship :-)
>
> I rather would advice Rogers to consult a specialist, and when
> indeed stereopsis is impossible, to develop a "wobble" viewer,
> or practice wobble projection with his many stereo slides.
> (The wobble issue has been discussed on the list a few
> months ago.)
>
> Abram Klooswyk
>
>
>
>
>