The range of fusible horizontal disparities around the empirical horopters

The range of horizontal disparities for which single vision is experienced, referred to as Panum´s fusional range, increases in the left and right periphery and is approximately symmetrical around the empirical horizontal horopter. No corresponding data have been published specifying the range and locus of symmetry for the range of fusible horizontal disparities for locations above and below the horizontal plane of regard. We mapped the empirical horizontal and vertical horopters using a minimum motion paradigm and then measured the fusional volume in the horizontal plane of regard and for locations in the median plane above and below the fixation point. We show that the fusional range of horizontal disparities increases to the left and right, and above and below fixation and is symmetrical about the empirical horizontal and vertical horopters.