T3D acuity enhanced with binocular vision

[Peter Abrahams <telscope@xxxxxxxxxx>]

In times past, this list has discussed the enhancement of vision when both
eyes are used, as compared to monocular vision.  (Enhanced in addition to
the potential for stereoscopy).  I had read conflicting reports on whether
acuity was improved with binocular vision.  I recently found a seemingly
authoritative article on the subject.

Binocular Enhancement of Visual Acuity.  Ron Cagenello, Aries Arditi, & D.
Lynn Halpern.  Journal of the Optical Society of America A, vol. 10, #8,
1993, pp1841-1848.  Using both eyes as compared to one, perception of
contrast increases by 40 to 50 percent.  Reaction time and perception of
luminance can increase by 30-70 per cent.  Tests by R. Home found 40 per
cent increase in acuity with binocular vision at very low contrast levels
of one per cent; but when contrast levels were higher than 30 per cent, the
increase was about 9 per cent.  Other tests, with a chart similar to the
standard eye test chart with lines of increasingly small letters, showed
improvement of about ‘one half of a line’ in acuity.

The published test measured acuity, using block letters on a computer
monitor and a Stereographics stereo display program.  Letters use lines of
varying orientation and spatial frequency (finer & closer lines, or coarser
& widely spaced lines).  The test subjects viewed the letters through a
Minolta 10 x 25 binocular, used backwards to decrease size.  (Item of
interest: They tested the Minoltas at 65 per cent transmittance).  
At high contrast levels, all subjects had improved acuity using both eyes.
However, at lowest contrast levels, two out of four subjects showed
superior acuity using only one eye.  All also showed improved acuity with
increased contrast at all levels.  
They also tested for acuity when presenting one eye with a high contrast
target, and the other eye with a low contrast target.  Acuity improved as
contrast to one eye was increased, and ‘performance was governed by the eye
that received the higher contrast’.  However, in this test, acuity was
higher than in the monocular test, so the low contrast eye also
contributed.  Acuity was increased the most when contrast was the same for
both eyes, decreasing as contrast disparity was increased.

Pupil size must be controlled, since a larger pupil will reduce resolution
because of the aberrations of the eye.  Earlier tests covered one eye for
the monocular test, which causes an increased pupil size in the uncovered eye.

Overall, acuity increased by 11 percent when viewing with both eyes,
compared to viewing with one eye (a letter 11 percent smaller could be
read).  The authors say that this is in general agreement with other studies.
This figure might sound low but is significant.

_______________________________________
Peter Abrahams   telscope@xxxxxxxxxx
the history of the telescope, the microscope,
    and the prism binocular


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End of TECH-3D Digest 271
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