Non-visual variables in binocular performance
Date
2015-08-07
Authors
Humphriss, Deryck
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Abstract
Clinical workers in binocular vision , known as o rth o p tis ts , have
noticed variations in the binocular performance of patients which appear
to have no relation to the ir visual state. Similarly there are some
binocular tests, in p a rticu la r stereoscopic tests, which cannot be
performed by normal students of the Optometry School.
An in it ia l reading of the literature on binocular vision indicated
that i t can be divided in to two parts, that concerning the mechanism
which produces one visual percept from two visual inputs to the two
separate eyes, and the mechanism which produces stereopsis, by evaluating
the angular differences between the two re tin a l images and interpreting
them as a sense of depth.
I t was decided to concentrate on the haploscopic aspect of binocular
vision , and to search fo r non-visual variables which determined the
operation of th is function.
A detailed reading of the lite ra tu re brought to lig h t several sets of
experimental results showing marked v a ria b ility between normal subjects
on the same te s t. Some of the operators commented on these, but did not
look fo r th e ir o rig in .
The neurological and neuro-anatomical lite ra tu re indicated that
the production of the single visual percept was an on-going process which
became more complex as i t was passed to higher neurological levels u n til
the fin a l process was controlled by the cortex of the parietal lobe.
This suggestion was confirmed by an E.F.G. programme carried out by
the w rite r.
The existence of neurological a c tiv ity in the parietal cortex
involving the in h ib itio n processes which remove an unwanted diplopic
image from visual perception suggested very strongly that psychological
variables would be found here.
This survey of the lite ra tu re also indicated that no previous work
had been done in this fie ld and new tests had to be devised to isolate
and measure the non-visual variables. This programme was undertaken by
the w rite r who had done previous research in orthoptics and in optometry.
These tests produced 20 scores, some of which suggested the psychological
variable with which the optometric scores might correlate s ig n ific a n tly .
The nature of these scores was described to a cross-discipline
project team whose members designed a battery of tests, one psychological
and the other neuro-psychological.
The psychological battery was based on the assumption that the
variable appeared to re late to some sort of psychological r ig id ity , but
that as th is was not certain, certain other tests such as motivation,
fru s tra tio n and suggestion must be adequately covered.
The neuro-psychological battery assumed that the binocular variables
must be measurable in the a c tiv ity of the central nervous system, and might
appear as the muscular control of movement, or in the speeu of perception.
A battery of te sts, including the E.E.G., was designed to measure these
functions.
The to ta l testing programme was now very large, and was given to
two p ilo t samples. The battery was reduced in size by a study of the
correlations, and by the use of cluster analysis. A study of the
selected co rre la tio n between the binocular and the psychological
scores indicated a relationship between the psychological results and some
of the binocular tests.
A reduced battery of both tests was given to a larger sample and
a fa cto r analysis of the re su lt selected perseveration as the major
psychological variable in binocular performance.
During the course of the research work some very valuable discoveries
were made fo r c lin ic a l optometry. The possible value of the results to
psychology and the avenues of future research opened up by the programme
of research are discussed.
Description
A Thesis presented to the Faculty of Science of the University of the
Witwatersrand fo r the Degree of Doctor uf Philosophy.
January 1979