This experiment was designed to study the extent to which precise binocular fixations as measured by lateral fixation disparity could be trained by means of visual feedback. Twenty subjects were trained to minimize their own fixation disparity responses by introducing an intermittent binocular stimulus into the display field which reduced fixation disparity to within 2' of arc. Introduction of the intermittent control stimulus was paired with an immediate visual feedback to the subject. This allowed the subject to be aware irnmediately of his own vergence responses. Transference of the practice effect was studied by: (l) plotting individual and group learning curves where frequency of the intermittent control stimulus was plotted as a function of time (training sessions), (2) change in the average magnitude of fixation disparity measured at 4.25 m1 40 em and 20 em, (3) graphical comparison of the patterns of lateral fixation disparity (Ogle, et al, 1970) resulting from induced lateral prism and lenses at 4.25 m and 40 em. Training of subjects to meet specific criteria varied from two to four weeks. Persistence of the practice effects was tested one and six weeks after the completion of training. Significant differences (~=.05) were found in the average magnitudes of fixation disparity at the three test distances and in the patterns of lateral fixation disparity.
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