Visual and non-visual factors in peri-saccadic compression of space

The perceptual stability of visual space becomes fragile in the wake of a saccadic eye movement. Objects flashed shortly before a saccade are mislocalized towards the saccade target. Traditional accounts for this effect have associated the mislocalizations with a sluggishness of the efference copy signal, which is important in space perception across eye movements. Recent theories of space perception, however, have emphasized a role of visual memory in the generation of trans-saccadic spatial stability. We have investigated the role of visual processes in the peri-saccadic compression of space. In our experiments, subjects performed saccades in front of a computer display while visual stimuli were briefly flashed on the screen just before or during the saccade. Subjects had to report the perceived location of the flash. When the saccade target's position was visibly available after the saccade, the perceived location of the flash was compressed towards the target's position. This compression occurred along the axis of the saccade, but for parts of visual space also along a direction orthogonal to the saccade. When the saccade target was not available after the saccade, the perceived location of the flash showed only a slight shift in saccade direction. In this condition, however, the perceived location of the saccade target itself was drawn towards the position of the flash. We propse a framework to explain these findings by a combination of preand post-saccadic processes.