While visuomotor adaptation to visual direction alteration by lateral prisms has been widely studied, the mechanisms underlying visuomotor adaptation to alteration of apparent distance remain poorly known. We performed a series of psychophysical studies to explore the short-term components of adaptation to alteration of apparent distance. Base-out prisms were used to alter apparent distance by modifying vergence demand. By manipulating visual feedback, we were able to demonstrate three adaptation levels: 1) changes in perceived distance related to increased tonic vergence induced by sustained vergence (eye muscle potentiation); 2) a recalibration of the altered distance signal derived from vergence by limb proprioceptive-motor signals; 3) a reorganization of motor commands of the upper limb used. No limb proprioceptive component was identified. The nature of adaptive components to apparent distance alteration differs from that classically described for visual direction alteration, which involves essentially proprioceptive and motor components. This difference can be attributed to differences in accuracy between proprioception and vision for localization in depth or in lateral directions. The geometrical aspects of distance perception based on vergence were explored by comparing visual adaptation to base-out prisms (introducing an offset in vergence demand) and to a telestereoscope (multiplying vergence demand for all fixation distances). Regardless of which optic device was used, the recalibration of the relationship between the vergence signal and perceived distance consisted in a constant bias over distances.
