Human transsaccadic visual processing: presaccadic remapping and postsaccadic updating

With every movement of the eye the visual field is drastically displaced in space. However, our visual experience is stable rather than constantly jittering with every saccade. One neural mechanism thought to underlie such spatial constancy across saccades is predictive remapping in which visual receptive fields remap to non-classical future locations in anticipation of a forthcoming saccade. We investigated mechanisms of predictive remapping in humans using a cross-hemispheric remapping paradigm. EEG was recorded while subjects performed a task requiring leftward and rightward horizontal saccades in the presence of salient peripheral stimuli. Saccades caused the peripheral stimuli to either shift between the two visual hemifields (Cross condition), necessitating remapping between cerebral hemispheres or to shift within a single visual hemifield (Within condition), requiring remapping only within a single hemisphere. Saccade-locked event-related potentials were calculated for each of these conditions. A baseline saccade-only condition was subtracted from experimental conditions to isolate remapping activity from activity related to saccade planning and generation. In a presaccadic time window difference waveforms were consistent with predictive remapping, exhibiting an ipsilateral positivity in the Cross condition and a contralateral positivity in the Within condition. This result is consistent with the occurrence of remapping in advance of a saccade. A similar pattern was also apparent in an intrasaccadic time window suggesting that predictive remapping persists during saccadic execution. Examination of postsaccadic visual responses revealed that hemispheric distributions of Cross and Within conditions matched the distribution of the corresponding presaccadic remapping response suggesting that the pressacadic response indeed reflects a shift of visual representations to match that of postsaccadic space.