AN ADAPTABLE ASSOCIATION BETWEEN VERTICAL AND HORIZONTAL VERGENCE

Vertical phoria (vergence error under monocular viewing conditions) ca n be trained to vary with conjugate eye position. The adaptive respons e controls the vertical alignment of the two eyes in the absence of bi nocular disparity and is used to compensate for binocular changes of t he oculomotor system induced by developmental and environmental factor s. Vertical phoria was associated with horizontal disparity vergence b y adapting vertical vergence to two vertically disparate targets separ ated along the depth axis. This association was primarily dependent on the horizontal vergence as opposed to monocular eye position or binoc ular conjugate eye position. Following this adapted association with h orizontal disparity vergence, vertical phoria aftereffects were also e voked by accommodative vergence, Previous reports have demonstrated an adapted association between vertical phoria and conjugate eye positio n, The current report examines the difference in the vertical phoria r esulting from adaptation to vertically disparate targets separated alo ng either the vertical axis or depth axis. The amplitude of the vertic al vergence aftereffect was approximately 4 times greater for targets separated along the depth axis than in the vertical meridian. The asso ciation between vertical phoria with conjugate eye position and horizo ntal vergence is proposed to result from a cross-coupling of vertical vergence with supranuclear regions that control conjugate and horizont al vergence eye movements. A selective interaction would enable the oc ulomotor system to correct disturbances in specific supranuclear regio ns as they interface with vertical vergence.