THE TIME COURSES OF VISUAL MISLOCALIZATION AND OF EXTRARETINAL EYE POSITION SIGNALS AT THE TIME OF VERTICAL SACCADES

Ah&act--The time course of perceptual miskalization at the time of vertical saccades was compared with that reported previously for horizontal saccades. Despite the difference in the oculomotor system involved in generating these saccades with different directions, the time course of the perceptual mislocalization and that of the extraretinal eye position signal estimated on the basis of visual misl~li~tion were the same between vertical and horizontal saceadcs. The results are discussed in relation to the outflow theory of subtraction, and it is argued that there is a common neural center for producing extraretinal eye position signals for both vertical and horizontal saccades. Vertical saceade Visual stability Eye position signal Position constancy IN’IRODUCTION When we change the direction of our gaze in the visual field, the stationary objects do not nor-mally appear to move, in spite of the changed positions of their images on our retinas. This phenomenon is well known as “position con-stancy”. A classical and most pervading expla-nation for this phenomenon is the subtraction theory that was suggested by Helmholtz (1866). The subtraction theory explains that the shift of visual images on the retina at the time of eye movements is canceled by an extraretinal eye position signal (EEPS), resulting in visual stability. Many psychophysical experiments, however, have failed in showing visual stability at the time of a saccadic eye movement. In typical experiments, avisual target is flashed in the dar