Rapid eye movements called saccades give rise to sudden, enormous changes in optic information arriving at the eye; how the world nonetheless appears stable is known as the problem of spatial constancy. One consequence of saccades is that the directions of all visible points shift uniformly; directional or 2D constancy, the fact that we do not perceive this change, has received extensive study for over a century. The problems raised by 3D consequences of saccades, on the other hand, have been neglected. When the eye rotates in space, the 3D orientation of all stationary surfaces undergoes an equal-and-opposite rotation with respect to the eye. When presented with a an optic simulation of a saccade but with the eyes still, observers readily perceive this depth rotation of surfaces; when simultaneously performing the corresponding saccade, the 3D orientations of surfaces are perceived as stable, a phenomenon I propose calling 3D spatial constancy. In experiments presented here, observers viewed ambiguous 3D rotations immediately before, during, or after a saccade. The results show that before the eyes begin to move the brain anticipates the 3D consequences of saccades, preferring to perceive the rotation opposite to the impending eye movement. Further, the anticipation is absent when observers fixate while experiencing optically simulated saccades, and therefore must be evoked by extraretinal signals. Such anticipation could provide a mechanism for 3D spatial constancy and transsaccadic integration of depth information.depth perception ͉ vision ͉ saccades ͉ spatial constancy D irectional or 2D spatial constancy holds insofar as the uniform, 2D shifts of the retinal image accompanying each eye movement (see Fig. 1a) do not lead to perceptions either of change in direction of individual points or of 2D motion. This type of spatial constancy was noted by Descartes in his Traité de l'Homme and has been studied systematically since the 19th century (refs. 1-3 and see refs. 4-8 for reviews). Distortions in spatial vision in the temporal vicinity of saccades are considered as signs of processes that give rise to constancy. For example, the threshold for perceiving motion rises just before a saccade (9, 10), which may be why motion is usually not perceived after saccade-induced retinal shifts, and may allow for optimal transsaccadic integration of information (11). Furthermore, points flashed around the time of a saccade are systematically mislocalized in a way that suggests slow build-up of compensation for retinal shifts (12)(13)(14)(15)(16)(17)(18)(19). The dynamic properties of neurons that remap their receptive fields in the anticipation of saccades may be closely connected with these distortions and contribute to spatial constancy (7). Such neurons have been found in posterior parietal cortex (20)(21)(22), superior colliculus (23), and the frontal eye field (24) of monkeys; recently, neuroimaging has demonstrated similar spatial updating in human parietal cortex (25).An aspect of the spatial constancy problem that h...