The reference frames in saccade adaptation.

Saccade adaptation is a mechanism that adjusts saccade landing positions if they systematically fail to reach their intended target. In the laboratory, saccades can be shortened or lengthened if the saccade target is displaced during execution of the saccade. In this study, saccades were performed from different positions to an adapted saccade target to dissociate adaptation to a spatiotopic position in external space from a combined retinotopic and spatiotopic coding. The presentation duration of the saccade target before saccade execution was systematically varied, during adaptation and during test trials, with a delayed saccade paradigm. Spatiotopic shifts in landing positions depended on a certain preview duration of the target before saccade execution. When saccades were performed immediately to a suddenly appearing target, no spatiotopic adaptation was observed. These results suggest that a spatiotopic representation of the visual target signal builds up as a function of the duration the saccade target is visible before saccade execution. Different coordinate frames might also explain the separate adaptability of reactive and voluntary saccades. Spatiotopic effects were found only in outward adaptation but not in inward adaptation, which is consistent with the idea that outward adaptation takes place at the level of the visual target representation, whereas inward adaptation is achieved at a purely motor level.