Transient spatiotopic integration across saccadic eye-movements mediates visual stability.

Eye movements pose major problems to the visual system, as each new saccade changes the mapping of external objects on the retina. It is known that stimuli briefly presented around the time of saccades are systematically mislocalized, while continuously visible objects are perceived as spatially stable even when they undergo large trans-saccadic displacements. Here we investigated the relationship between these two phenomena and measured how human subjects perceive the position of pairs of bars briefly displayed around the time of large horizontal saccades. We show that they interact strongly, with the perisaccadic bar being drawn towards the other, dramatically altering the pattern of perisaccadic mislocalization. The interaction field extends over a wide range (200 ms and 20°) and is oriented along the retinotopic trajectory of the saccade-induced motion, suggesting a mechanism that integrates pre- and post-saccadic stimuli at different retinal locations - but similar external positions. We show how transient changes in spatial integration mechanisms, which are consistent with the present psychophysical results and with the properties of "remapping cells" reported in the literature, can create transient craniotopy by merging the distinct retinal images of the pre- and post-saccadic fixations to signal a single stable object.