We tested the ability of normal subjects to alter the conjugacy of the
ir saccades in a position-specific manner, Five subjects dichoptically
viewed a stereogram produced by two random-dot patterns, They immedia
tely perceived a three-dimensional wedge with its apex closer to them,
They were asked to saccade for 15 min back and forth between the apex
and two lateral dots of the wedge, For fixation sequences between cen
tre-right-centre, saccades immediately became larger in the right eye,
For sequences between centre-left-centre, saccades immediately became
larger in the left eye, For two subjects this non-monotonic position-s
pecific disconjugacy compensated for the disparity of the stereogram a
lmost perfectly, The disconjugacy persisted even under monocular viewi
ng of one of the random-dot patterns. It diminished or disappeared imm
ediately, however, when the random-dot pattern was shifted on the scre
en, We suggest the existence of a fast learning mechanism capable of p
roducing ;position-specific disconjugacy by associating saccades with
disparity, Such a mechanism would use a visual reference rather than t
he position of the eyes in the orbit.