Abstract
Saccadic adaptation affects the visual localisation of stimuli presented before an adapted saccade. The perceived location is shifted in the direction of adaptation. Factors that may be involved in the generation of the adaptation-induced shift include post-saccadic visual references, an efference copy signal, and adaptation of spatial localisation. If spatial localisation adapts concurrently with the saccade, a mislocalisation should be observable also during fixation. Most former studies, however, found only negligible shift during fixation in the adapted state. We studied visual localisation in a novel saccade adaptation paradigm in which a constant visual error is maintained throughout an extended session of 1000 adaptation trials. In this paradigm, the saccade landing position is predicted on-line during the saccade, and the target is jumped to a location that creates a fixed visual error. An initial target eccentricity of 13° and a constant visual error of 3° resulted in adaptation to a landing position near 10°. Localisation trials were intermixed in the course of adaptation. While the subject fixated a stimulus bar was flashed. The subject then reported the perceived location of the bar with a mouse pointer. Using this procedure we found mislocalisation during fixation that increased over the first 600 trials and reached up to 1.5°. We conclude that the adaptation of saccade amplitudes is accompanied by a partial adaptation of visual localisation that develops more slowly over time.