Patrik Polgári¹ (), Alexander C. Schütz¹; ¹University of Marburg

Position errors after saccades lead to adaptive changes in their programming. Two underlying mechanisms have been described, relating to the direction of error: Backward adaptation i.e., shortening of amplitudes, is stronger and has a quicker dynamic profile than forward adaptation i.e., lengthening of amplitudes. Moreover, saccade adaptation is described as direction-specific, meaning no transfer of adaptation from leftward to rightward saccades. However, classic studies adapted saccades only in one direction and from the same initial starting point. This paradigm limits a potential transfer of error information between adaptation mechanisms acting in opposite directions. In the first experiment, we tested whether adaptation in one saccade direction can interact with adaptation in the opposite direction. In a horizontal random walk paradigm, we simultaneously adapted observers’ leftward and rightward saccades in three conditions: (1) both-backwards, (2) both-forwards, and (3) backwards in one direction and forwards in the other (‘mixed’). We found an asymmetrical interplay between backward and forward adaptation occurring in opposite directions. While forward adaptation was similar in the ‘both-forwards’ and the ‘mixed’ conditions, backward adaptation was stronger in the ‘mixed’ condition compared to the ‘both-backwards’ condition. In the second experiment, we sought to discern whether these asymmetrical effects reflect backward adaptation being facilitated by forward adaptation or impaired by backward adaptation in the opposite direction. In three conditions, we combined backward adaptation in one direction with different adaptations in the opposite: (1) forward (‘mixed’), (2) backward (‘both-backwards’), and (3) no adaptation. We found reduced backward adaptation when coupled with backward adaptation in the opposite direction compared to forward or no adaptation. This replicates findings of the first experiment and suggests that simultaneous backward adaptation in opposite directions poses a particular challenge to the oculomotor system. Generally, saccade adaptation in opposite directions may not be as independent as previously assumed.

Acknowledgements: This work was supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - Project Number 222641018 - SFB/TRR 135 TP B2.