Updating for perception: An ERP-study of post-saccadic perceptual localization

With every eye movement the retinal positions of objects in our environment change, and yet we perceive the world around us as stable. Efference copies of motor commands are used to update the retinal positions across saccades. Saccadic updating after two successive saccades (oculomotor updating) has been shown to take place between the saccades and to involve parietal regions. However, there is evidence that updating of object locations across a single saccade (perceptual updating) may represent a distinct process. The present study investigated the timecourse and topographical organization of perceptual updating in twenty healthy human subjects by means of simultaneous eyetracking and event-related potential (ERP) recording. Participants were asked to perform single horizontal left- and rightward saccades and to subsequently localize a target perceptually that was briefly shown before the saccade. Successful completion of the task involved either intra- or interhemispheric updating of the target location. Localization was less precise when updating of visual space was necessary relative to a control condition with no updating requirement. In the updating condition, we observed a positive deflection over parietal electrode sites starting about 300 ms after saccade onset. This effect was more pronounced over right parietal electrode sites, corroborating findings of right hemispheric dominance in updating of visual space. While this component likely reflects memory of the updated stimulus location, we suggest that an earlier negative deflection occurring at about 100 to 180 ms after saccade onset may be more directly linked to the updating process. The need for interhemispheric transfer of target related information did not have an impact on either localization accuracy or magnitude of the associated ERP components. These results indicate that perceptual updating takes places shortly after the saccade, a finding which is similar to what has been observed for oculomotor updating.