Zinong Li^1,2,3 (), Michael Landy^2,3,4, Robert Volcic^1,5,6; ¹New York University Abu Dhabi, ²New York University, ³NYU Department of Psychology, ⁴NYU Center for Neural Science, ⁵NYUAD Center for Artificial Intelligence and Robotics, ⁶NYUAD Center for Brain and Health

INTRODUCTION. Saccades and reaches are tightly coordinated movements, yet the extent to which they share planning resources is unclear. METHODS. To investigate cross-effector interaction, we employed a motor-adaptation paradigm that applied concurrent perturbations to reaches and saccades. The perturbation amplitudes followed a sine wave time course across trials, with different temporal frequencies and orthogonal perturbation directions across effectors. Participants reached for a visual target with view of the hand and arm occluded and made a saccade to the target after reach completion. Saccade adaptation was triggered by displacing the target during the saccade, while reach adaptation was induced by altering the feedback of the reach endpoint relative to the original target location. By extracting reach and saccade errors as adaptation responses, we identified both spatial and temporal signatures of adaptation, confirming that each effector’s adaptation was successfully triggered. We fitted a sine wave to the sequence of adaptation responses using a maximum a posteriori criterion. The sine-wave frequency was fixed to match the perturbation frequency, and the posterior distribution of sine-wave amplitudes was computed using Markov Chain Monte Carlo sampling, providing credible intervals to assess the presence and magnitude of adaptation and transfer effects. RESULTS. Both reaches and saccades adapted to their respective perturbations. In addition, we found that reach responses also mirrored the temporal and spatial signature of the saccade perturbation: a transfer of saccade adaptation to reach planning. In contrast, reverse transfer from reach adaptation to saccade planning was not observed. CONCLUSIONS. Our approach provides a sensitive method to quantify adaptation effects that can help resolve previous conflicting results. The observed asymmetry may stem from an asymmetry of the control of saccades vs. reaches in natural behavior such that saccade planning influences reach planning, but not the converse.

Acknowledgements: We acknowledge the support of the NYUAD Center for Artificial Intelligence and Robotics and the NYUAD Center for Brain and Health, funded by Tamkeen under the NYUAD Research Institute Awards CG010 and CG012. We acknowledge the support of NIH grant EY08266 (MSL).