The role of eye-movements in stereoscopic perception of space, other than that of bi-foveal fixation of the object of regard, is discussed. First, it is shown that global fusion and bi-foveal fixation are demonstrably different responses; in pursuit of global fusion, the angle of convergence may be so changing as to shift the intersection of the two visual axes towards a point in space where no object is to be found. Second, a highly accurate change of vergence in tracking an object moving in depth does not, in itself, produce perception of object motion; a certain critical change in vergence must be required, to initiate perceived motion. This "program newness", expressed in terms of a fast retinal image displacement producing a step in retinal disparity, equals, at least, 2 min arc per 0.1 sec of vergence reaction time. A hypothesis is advanced, in the general framework of prediction-oriented theories of perception, to interpret vergence eye-movements as also a means of neutralization of the input "unwanted" by the visual system.