Different motor systems use similar damped extraretinal eye position information

Extraretinal eye position information (EEPI) shifts the directional significance of retinal loci by an angle roughly equal to that of an associated saccade, with the shift reported to begin 0-250 ms before the saccade and to continue apace with the saccade, or sluggishly, over a period as much as an order of magnitude longer. These different estimates of remapping initiation and duration could be due to various factors, including different localizing responses, retinal loci of probe flashes, and saccade target predictability. We compared manual and gaze pointing to probe flashes at controlled retinal loci under identical stimulus conditions and in the same subjects, and found that EEPI was similar: both hand and gaze pointing EEPI shifted over about 140 ms, beginning about 50 ms before the saccade. For both pointing responses, remapping appeared to be initiated later for parafoveal loci than for loci 10 degrees to either side. We found no effect of saccade target predictability. We show that variability in EEPI and sensory processing only slightly (similar to 5%) inflates estimates of EEPI shift duration. Based on our results, and comparisons with recent studies, we argue that similar EEPI parameters apply to hand pointing, eye pointing and visual comparisons, and that remaining differences across studies can reasonably be attributed to differences in stimulus conditions. (C) 1998 Elsevier Science Ltd. All rights reserved.