Abstract:
The problem. Traditional subjective visual acuity
tests are not effective in testing nonverbal, profoundly retarded individuals. The present paper investigated the use of operant conditioning procedures in determining threshold crossings and compared the effectiveness of the staircase and descending series stimulus presentation methods, using a two-response paradigm.
Procedure. Three profoundly retarded and two mildly retarded individuals were trained to discriminate between a right-facing E and an upward-facing E, using stimulus fading and reinforcement procedures. The participants indicated the presence of a given stimulus by responding on one of two levers or drawing the E as displayed. Correct responses resulted in praise and an edible reinforcer. Incorrect responses were followed by a 10 second time-out and the reinforcer was withheld.
Findings. Correct responses reached the established criterion during the right-facing E versus blank card condition only after the implementation of instructions and time-out procedures. The upward-facing E was faded onto the
blank card and the distance from the participants was increased to ten feet without significant difficulties. The threshold crossings obtained with three participants were reliable within and across the type of stimulus presentation method used. The threshold crossings produced with the
staircase method were similar to or lower than those produced with the descending-series method. The threshold estimations obtained with the present procedures were similar to or lower than those obtained by an ophthalmologist using the Snellen chart.
Conclusions. The instructions and time-out procedures appeared to be significant variables in obtaining stimulus control over responding. The present procedures must be further refined before application to applied settings due to the extended time spent in training.
Recommendations. Procedures for testing visual acuity in the profoundly retarded must include a means to promote attention to the stimuli. Future research should investigate the significance of simple instructions and time-out procedures and testing between sessions (Test B) in visual acuity assessments.
