Smooth eye movements and spatial localisation

We asked subjects to align a target that flashed as their eyes rotated to t he right in pursuit of a moving ring, with a target that flashed as their e yes rotated to the left in pursuit of the ring. Subjects systematically mis localised the targets in the direction of pursuit. When the ring and flashe s were the only structures that were visible, the alignment error was about 4 cm, corresponding to a timing error of about 100 ms. The timing error wa s independent of the position along the ring's path, but did depend to some extent on pursuit velocity. Adding a textured background reduced the mislo calisation considerably, presumably because it enabled subjects to localise the targets relative to the surrounding. There was almost no mislocalisati on if the subject was not pursuing the ring. It is suggested that the mislo calisation arises because incoming retinal signals are combined directly wi th outgoing oculo-motor commands, with no attempt to account for any of the involved neuronal and muscular delays. (C) 2001 Elsevier Science Ltd. All rights reserved.