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456
AM J OPTOM & PHYSIOL OPTICS
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Vol. 65.
No. 6
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trast)
cues were
superimposed;
they were gradually eliminated after correct responding. Eventually all monocular cues were removed,
requir
ing the patient to respond only to stereoscopic cues. It was found that the percentage of correct responses to stereo targets was improved dramatically with reinforcement. Most children aged 3 years or older were able to respond süccessfully to a RDS presented in this manner. Nonreinforced responses
to
stereograms
were poorer
and
more variable. Cooper
and Feldman2
concluded that
RDS
presented in an operant conditioning
paradigm
were particularly effective in evaluating binocular responses and detecting a constant strabismus because RDS do not contain any monocular cues
and require
bifoveal alignment for perception (Table 1).
In a
later
study, Feldman and
Cooper
modified their automated
operant
RDS technique by utilizing errorless discrimination along with
cue
fading techniques.3 This time both the RDS containing disparity (5+)
and
a RDS lacking disparity (S—) were
presented
simultaneously (Figs. 1
and
2). The left to right location of the Si+ was
altered
randomly. Patient responses were made by breaking an infrared photocell beam when the child tried to touch the stimulus. Both the contrast of the monocular
cue in
the
stereoscopic RDS and
the contrast of the incorrect stimulus (no
stereo,
S—) were reduced; that is, the monocular cue faded out while the contrast of the S— was faded in. The technique enabled valid and reliable responses in children as young as 2½ years of age. Traditional testing techniques that
required an experienced
doctor or technician resulted in no responses or unreliable responses in many
children
under 4 or 5 years of age.
TABLE
1.
Number of patients passing or failing the operant RDS dlscñminatlon
test according
to
visuai diagnostic dassification.
• Normal
refers
to patients whose visual diagnosis did not include a strabismus (constant or
Intermittent).
amblyopia. or ocular pathology.
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Similar computerized
techniques
have also been used by others. Fox et al.4
used
computer- generated dynamic
RDS
with a preferential viewing procedure in order to
investigate
binocular responses in infants. Their subjects viewed the dynamic
RDS
while wearing red-
green
anglyph glasses. A stereoscopic vertical bar was moved from the center position to
the
left or right. A trained observer viewed the position of the infant’s eyes. Appropriate fixation, i.e., movement of the eyes corresponding to the position of the vertical bar, signified stereoscopic appreciation. Stereopsis
was
demonstrated in infants as young as 6-months-old.
The experiments by Cooper
and Feldman1-3
and Fox et al.4 demonstrated that appropriate stimulus presentation
associated
with effective reinforcement could be used to investigate bin. ocular vision in patients who lacked sophisticated communication skills. Both research
groups used
computerization to present
and
manipulate stimuli, and to present reinforcement when necessary. Computerization
was required
to make rapid,
almost
instantaneous changes in stimulus
parameters
and
to
provide immediate feedback of reinforcement.
Manual
techniques would have
been
too slow
and
arduous.
In another experiment,
Cooper and
Feldman5 used their operant conditioning techniques with automated presentation of
RDS to
determine if vergence training resulted in an increase in ver
gence
ranges. They
used
an A-B reversal
design
to control for placebo effects. The experimental group (A) received vergence training; the control
group did
not (B). During vergence training, correct responses
resulted
in positive reinforcement
and
a concurrent increase in vergence demand, whereas incorrect
responses
resulted in a reduction of vergence
demands.
The control group
received
the identical stimuli and reinforcement; however, neither correct nor incorrect responses resulted in any alteration of vergence demand. Their results demonstrated that automated convergence training
yields a rapid
increase in maximum convergence range, whereas placebo training does not. Furthermore, patients who improved their vergence ranges using
this
system
transferred
their ability to other vergence tasks involving
vectograms and prisms. Cooper and
Feldman also demonstrated that patients who
did
not respond to
traditional
orthoptic therapy were
treated
successfully
with automated
vergence training (Fig. 3).
Recent research by Dawn et aL supported Cooper and Feldman’s previous work that computerized convergence training improves positive fusional vergences. Dawn et al. demonstrated transfer of improved vergence abilities on
prism bar and amblyoscope
testing devices.
In a later clinical study
Cooper
et al.7
designed
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