Comparing limb proprioception and oculomotor signals during hand-guided saccades |
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Authors: | L Ren G Blohm J D Crawford |
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Institution: | (1) Centre for Vision Research, York University, Rm. 0003C, Computer Science and Engineering Bldg, 4700 Keele Street, M3J 1P3 Toronto, ON, Canada;(2) Departments of Kinesiology and Health Science, York University, 4700 Keele Street, M3J 1P3 Toronto, ON, Canada |
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Abstract: | We previously showed that saccades tend to overshoot briefly flashed targets that were manually displaced in the dark (Ren
et al. 2006). However it was not clear if the overshoot originated from a sensory error in measuring hand displacement or from a premotor
error in saccade programming, because gaze and hand position started at the same central position. Here, we tested between
these hypotheses by dissociating the initial eye and hand position. Five hand/target positions (center, far, near, right,
left) on a frontally-placed horizontal surface were used in four paradigms: Center or Peripheral Eye-hand Association (CA
or PA, both gaze and right hand started from the center or a same peripheral location) and Hand or Eye Dissociation (HD or
ED, hand or gaze started from one of three non-target peripheral locations). Subjects never received any visual feedback about
the final target location and the subjects’ hand displacement. In the CA paradigm, subjects showed the same overshoot that
we showed previously. However, changing both initial eye and hand positions relative to the final target (PA) affected the
pattern, significantly altering the directions of overshoots. Changing only the initial position of hand (HD) did not have
this effect, whereas changing only initial eye position (ED) had the same effect as the PA condition (CA ≈ HD, PA ≈ ED). Furthermore,
multiple regression analysis showed that the direction of the ideal saccade contributed significantly to the endpoint direction
error, not the direction of the hand path. These results suggest that these errors do not primarily arise from misestimates
of the hand trajectory, but rather from a process of comparing the initial eye position and the limb proprioceptive signal
during saccade programming. |
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Keywords: | Saccade Limb proprioception Hand displacement Update |
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