Apr11 1980 Training Fusional Convergence—Cooper & Feldman 207

100 dot matrix slides (2 X 2) photographically reproduced from those pictured in Foundations of Cyclopean Perception.8 The RDS slides were used to create two different pairs of stimuli. One pair contained a right and left slide so that binocular viewing resulted in a dot pattern seen with a central square in crossed disparity (660 sec of arc). The second pair contained two identical right eye slides paired so that no binocular disparity was present.

The RDS slides (average luminance = 816 cd/rn2) were projected by two Kodak model #650H Carousel projectors and were reflected off two 3.8 x 4.4 cm moveable front surface mirrors 8 cm from the projector. The mirrors could be automatically turned in small increments to create a base out fusion stimulus of from 0 to 40 prism diopters.

After the images were reflected by the mirrors, the images were passed through two linear polarizing filters mounted in front of the projector lenses at axis 45 and 135. The RDS was then rear-projected onto a 78 cm x 68 cm piece of clear Plexiglas sandblasted on the rear surface. Each patient was seated 40 cm from the Plexiglas screen so that the RDS subtended an angle of 10.2 deg to the patient.

Programming and sequencing of the stimuli, movement of the mirrors to alter fusional demands, delivery of reinforcers, and recording of the responses and trials were controlled by BRS solid state logic (TECH SERV, INC.) and electromechanical relay circuitry. Reinforcers were delivered by a BRS penny dispenser placed on the side of the viewing screen 70 cm from the child. Responses were made on two BRS illuminated push panels. The panels were 20 cm from the child and tilted 45 deg from horizontal. The right panel contained a centered two-dimensional darkened square. The left panel contained no square.

Procedure

During the first experimental session, the child wore polarizing glasses and was instructed to look at the screen. He was told that he would sometimes see an RDS containing an inner square “popping out” (crossed disparity; base out) and sometimes an RDS with no inner square (lacking ste

reoscopic disparity). During each experimental training session the two RDS’s were presented successively. Each RDS appeared an equal number of times, but in random order, during a session. A correct response to the stimulus (indicated by an appropriate panel push) by the child resulted in the immediate delivery of a penny from the penny dispenser, the onset of a 3- sec positive feedback light cue, and verbal praise by the examiner. If that correct response was made to the RDS containing the inner stereo square, it also resulted in a movement of the mirrors which increased the convergence demand by 0.66 on the next trial. No such mirror movement occurred for a correct response to the RDS without disparity. The first trial of each training session always contained an RDS in which the right and left views were superimposed, i.e., an RDS with a zero convergence demand from Donder’s line. An incorrect response to either RDS resulted in the termination of the trial and stimulus presentation without delivery of a penny, the 3-sec cue light, or verbal praise. In addition, any incorrect response also resulted in a decrease in the convergence demand by 1.32 pd on the following trial (up to the limit of zero demand). The failure of a child to make any response within the maximum 10-sec trial period was also considered as an error. The interval between trials, when the screen was dark, was fixed at 7.5 sec. Each experimental training session lasted approximately 20 min and contained about 100 trials or stimulus presentations. The final level of convergence demand reached was recorded (in prism diopters) at the end of each session. At this time the child was always given either a small toy or a number of pennies. If the pennies were selected, the exact amount was determined by the child’s level of performance during RDS convergence training. Following the experimental session, vectograrn base out (BO) ranges were measured (blur, break, and recovery points in prism diopters) using the Topper vectogram (Bemell Corp.).

RESULTS

Fig. 1 illustrates a typical initial RDS convergence training session of a child.