Distance cues for vertical vergence adaptation

Vertical vergence can be trained to respond to vertical and/or horizontal conjugate eye position, horizontal vergence, and vertical head tilt. This cross-coupling is manifest as a vertical phoria aftereffect (monocular vertical vergence response) that varies with direction and distance of gaze. The function of the spatially dependent adaptation is to maintain the calibration between vertical eye alignment and intended placement of the two retinal images. Oculomotor adaptation stabilizes our sense of spatial localization and calibrates a body-referenced coordinate representation of visual space that is necessary for visually guided motor responses. We have tested the possible association of vertical phoria adaptation with perceptual cues to distance in the absence of any other associated motor activity. During adaptive training, vertical disparity vergence was associated with variations of perceptual distance cues (including loom, overlap, relative size, and relative motion), oculomotor distance cues (horizontal vergence), or a combination of both classes of cues. We observed that in a 2-h period the open-loop (monocular) vertical vergence response could not be trained to occur as an aftereffect in association with the perceptual cues to distance, whereas it could be trained in association with oculomotor cues. We conclude that the spatial specificity of vertical vergence aftereffects caused by short-term adaptation results from an associated cross-coupling with supranuclear sources of oculomotor activity.