Re: Focus/fixation tolerance

[T3D Andrew Woods <andrew@xxxxxxxxxxxxxxxxxxxxx>]

John Merritt wrote:
>I would like to serve as a collection/collation point
>for any references or anecdotes related to the variation
>among individuals for mismatch between ocular focus and
>ocular fixation  (visual accommodation and convergence).

Here is a collection of references which I can immediately put
my hands on...

`Relation between Accommodation and Convergence' pp.96-97 in Boff & Lincoln 
"Engineering data compendium: Human Perception & Performance"
Wright-Patterson Air Force Base, OH, 1988.  (also other references in
other sections)

Yeh & Silverstein, 1990, "Limits of Fusion and Depth Judgement in Stereoscopic
color displays", Human Factors 32(1), 45-60.

Yeh & Silverstein, 1989, "Using Electronic Stereoscopic color displays: 
Limits of Fusion and Depth Discrimination", in "Three Dimensional Visualisation
and Display Technologies" Proceedings of the SPIE vol. 1083, pp.196-204.

Hiruma & Fukuda, 1993, "Accommodation responses to binocular stereoscopic TV
images and their viewing conditions" SMPTE Journal, 102(2), pp.1137-1144.

Nagata, 1996, "The binocular fusion of human vision on stereoscopic displays -
field of view and environmental effects", Ergonomics, 39(11), pp.1273-1284.

Head Rotation:
Isono & Yasuda, 1990, "Flicker free field-sequential stereoscopic tv
system and measurement of human depth perception", SMPTE Journal, 
February 1990, pp136-141.

Oh, and of course my paper:
Woods, Docherty & Koch, 1993, "Image Distortions in Stereoscopic Video Systems"
in "Stereoscopic Displays & Applications IV", Proc. SPIE vol. 1915.  (also
available from http://info.curtin.edu.au/~iwoodsa )

>The Boeing guide for the design of photointerpretation equipment
>suggests a liberal limit of 0.75 diopters mismatch between
>the observer's focus distance (usually taken to be the screen
>in a stereo display) and the observer's fixation distance,
>which could be either on the screen or in front of or behind the
>screen.

How does a diopter figure relate to the difference between two distances?
OK, I can guess, but It'd be nice to know for sure...

>It would be nice to have a family of curves showing how long
>it takes for various percentages of the population to become
>aware of discomfort when viewing various degrees of discrepancy
>between where the eyes are focused and where they are fixated.

This would be nice but I think it would have to be a very large
single study to obtain data like this.

>Too little caution will result  in rejected and cursed 3D display 
>systems, whereas too much caution results in very shallow depth
>viewing volumes, or overly conservative camera separation (with
>resulting limited depth acuity).

Too true.  It's not quite a knife edge balancing act but it is still
a difficult choice.  

Good Luck John.

Andrew Woods.


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