THE USE OF EGOCENTRIC AND EXOCENTRIC LOCATION CUES IN SACCADIC PROGRAMMING

Theoretically, the location of a visual target can be encoded with res pect to the locations of other stimuli in the visual image (exocentric cues), or with respect to the observer (egocentric cues). Egocentric localization in the oculomotor system has been shown to rely on an int ernal representation of eye position that inaccurately encodes the tim e-course of saccadic eye movements, resulting in the mislocalization o f visual targets presented near the time of a saccade. In the present investigation, subjects were instructed to localize perisaccadic stimu li in the presence or absence of a visual stimulus that could provide exocentric location information. Saccadic localization was more accura te in the presence of the exocentric cue, suggesting that localization is based on a combination of exocentric and egocentric cues. These fi ndings indicate the need to reassess previously reported neurophysiolo gical studies of spatial accuracy and current models of oculomotor con trol, which have focused almost exclusively on the egocentric localiza tion abilities of the brain.