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Gaelle N. Luabeya, Xiaogang Yan, J. Douglas Crawford; Influence of Gaze Direction and Saccades on Hand Location and Orientation Errors in a Memory-Guided Alignment Task. Journal of Vision 2020;20(11):866. doi: https://doi.org/10.1167/jov.20.11.866.
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The influence of gaze position/saccades on pointing and reach location have been studied extensively (e.g., Henriques et al., J. Neurosci. 1998), but their influence on grasp orientation has received less attention (Selen & Medendorp, Vision Res. 2011). Here we investigated the influence of gaze direction and saccades on hand location and hand orientation in a memory-guided alignment task. Participants (N=15) were instructed to reach and orient a hand-held rectangular 3D object against a 2D rectangular target with similar dimensions, presented briefly at two possible orientations (+45o or -45o from horizontal) at the center of an LED screen. Participants either maintained gaze fixation throughout the trial (toward a fixation point placed centrally or 10o left/right), or the fixation point shifted after the rectangular target disappeared, inducing a saccade just before the reach. Saccade trials were either centripetal (from 10o left/right toward center), centrifugal (center-out), or across fields, i.e., reversing the visual field location of the central reach target. Preliminary analysis confirmed a tendency to overshoot hand location in the direction opposite to final gaze location, during both fixation and saccade conditions, inducing a positive correlation between location errors in both tasks (Henriques et al. 1998). Hand orientation also tended to overshoot the orientation of the target rectangle. However, participants showed idiosyncratic gaze-dependent orientation errors: some showed little or no effect, whereas others showed inconsistent patterns. Further, final gaze-dependencies did not consistently correlate between fixation and saccade trials. In conclusion, this study extends the phenomena of ‘gaze-dependent overshoot’ and ‘gaze-centered updating’ (Henriques et al. J. Neurosci. 1998) to hand alignment. However, we found inconsistent evidence for gaze modulation of alignment, perhaps because the independent variable (horizontal gaze) was spatially independent from the dependent variable (clockwise / counterclockwise orientation). Further tests are needed to determine if this holds for other tasks.
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