DISTANCE CUES FOR VERTICAL VERGENCE ADAPTATION

Vertical vergence can be trained to respond to vertical and/or horizon tal conjugate eye position, horizontal vergence, and vertical head til t. This cross-coupling is manifest as a vertical phoria aftereffect (m onocular vertical vergence response) that varies with direction and di stance of gaze. The function of the spatially dependent adaptation is to maintain the calibration between vertical eye alignment and intende d placement of the two retinal images. Oculomotor adaptation stabilize s our sense of spatial localization and calibrates a body-referenced c oordinate representation of visual space that is necessary for visuall y guided motor responses. We have tested the possible association of v ertical phoria adaptation with perceptual cues to distance in the abse nce of any other associated motor activity. During adaptive training, vertical disparity vergence was associated with variations of perceptu al distance cues (including loom, overlap, relative size, and relative motion), oculomotor distance cues (horizontal vergence), or a combina tion of both classes of cues. We observed that in a 2-h period the ope n-loop (monocular) vertical vergence response could not be trained to occur as an aftereffect in association with the perceptual cues to dis tance, whereas it could be trained in association with oculomotor cues . We conclude that the spatial specificity of vertical vergence aftere ffects caused by short-term adaptation results from an associated cros s-coupling with supranuclear sources of oculomotor activity.