206 AM J OPTOM & PHYSIOL OPTICS Vol. 57, No. 4

SILO,~ localization,b float,c motion paral-

lax,” etc., represents actual sensory ability.

It may be the case that “correct” patient

responses reflect prompts from instruc-

tional sets or clinician questions, task de-

mands to “please” the therapist, therapist

bias in interpreting patient answers, the use

of monocular cues, etc. Thus, the use of line

or contour stimuli does not allow the clini-

cian to judge accurately the validity of the

patient’s response.6’7

Recently, a new type of stereogram has

been introduced which may solve some of

the problems indicated above. These ster-

eograms, called random dot stereograins

(RDS), contain a hidden stereoscopic geo-

metric form which can be appreciated only

under conditions of bifoveal fixation.8’9 Be-

cause they contain no monocular cues, they

are more likely to generate valid and relia-

ble patient responses than traditional vec-

tograms.

A second characteristic of traditional

convergence training procedures has been

their lack of concern with instituting formal

operations to facilitate patient motivation.

The success of therapy, especially for young

patients, often hinges upon the degree of

motivation they have for engaging in train..

ing exercises. Operant conditioning tech-

niques, which emphasize the use of re-

sponse contingent reinforcers to provide

motivation and immediate feedback for re-

sponding, have often been demonstrated to

facilitate learning and perfonnance.4,10,11

Its use in facilitating convergence training

and in improving convergence ranges has

not yet been explored.

A third feature of traditional convergence

training involves the actual method of

training. Although training usually entails

the presentation of progressively increasing

- SILO a perceptual phenomenon noted during

convergence and divergence. SI indicates that the

target appears smaller and closer upon convergence,

while LO indicates that the target appears larger and

further away upon divergence.

b Localization: the distance perception changes

which are due to vergence changes and are identified

by pointing to where the target appears to be.

Float:

the subjective response indicating that the

target appears to be suspended in space.

d Parallax: the apparent movement of the targets

when the subject sways. It is due to convergence or

divergence.

convergence demands and the use of infor-

mal prompts (e.g., the use of a pointer in

space to attain the appropriate degree of

ocular convergence), a concern for formal

programmed learning is usually lacking.

Operant discrimination learning, with its

emphasis on differential responding and

discrimination facilitation techniques, of-

fers a specific methodology which may en-

hance convergence performance.4

The use of RDS in an operant condition-

ing paradigm incorporating discrimination

facilitating techniques would seem to be an

effective method for improving conver-

gence ability and binocular vision, espe-

cially in children. The initial experiment

was conducted to determine whether that

procedure is more effective in improving

convergence than traditional vision training

or orthoptic techniques. A second study

was done in order to demonstrate that con-

vergence training, rather than just exposure

to stereograms, was the variable most re-

sponsible for improvement in convergence

ability.

EXPERIMENT 1

METHODS

Subjects

There were four male children between

the ages of 6 and 10. Three of these patients

were diagnosed as intermittent exotropes

and one as an accommodative esotrope

with poor fusion ranges. All had demon-

strated stereopsis (660 sec of arc) using the

operant RDS test described by Cooper and

Feldman.4 According to the clinicians re-

sponsible for vision training, none of the

children were making normal progress dur-

ing training sessions in regard to improving

convergence ability with vectograrns and

other standard clinical training procedures.

Each of the children had received at least

6 to 10 sessions of convergence training

using vectograms, prior to the experimental

intervention, in which fusions.! ranges were

recorded (all children had experienced ad-

ditional sessions where vectogram conver-

gence performances were unreported).

Apparatus

The RDS used for training convergence

during experimental sessions were 100 x