Nonlinear static model simulation of the fixation disparity curve

A nonlinear static interactive dual feedback model, containing deadspace operators representing the depth of field and Panum's fusional area (PFA), was developed to examine the effect of parameter variations on closed-loop fixation disparity. Four equations for fixation disparity were derived corresponding to the four combinations of deadspace operator outputs. It was found that the simulated fixation disparity lines separated into two pairs, with one pair for positive (exo) and the other for negative (eso) disparity. The curved shape of the experimental fixation disparity plot was found to be the result of the continual transition from the large-PFA exo line, through medium and then to small-PFA exo lines, as BO vergence stimulus decreased. It then crossed over to the small-PFA eso line, continuing through the medium and finally the large-PFA eso line as BI vergence increased.