| Abstract No.: | C-D3135 |
| Country: | Canada |
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| Title: | EARLY ONLINE CORRECTION IS SELECTIVELY INHIBITED BY LEARNING A NEW VISUOMOTOR TRANSFORMATION |
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| Authors/Affiliations: | 1 Valeriya Gritsenko*; 1 John Kalaska;
1 Université de Montréal, QC, Canada
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| Content: | Objectives: The study investigated the plasticity of the fast online correction mechanism that adjusts ongoing reaching movements in response to abrupt changes in the location of a movement goal. This mechanism is triggered even when subjects are unaware of the perturbation, and it resists voluntary modification (Pelisson et al., 1986 ; Day & Lyon, 2000). We studied how online correction is affected by learning a new visuomotor transformation.
Materials and methods: 24 subjects made planar pointing movements to visual targets without vision of the arm. Subjects were divided into three groups of 8 (C, V, and W groups). During the baseline block and test block of trials, all subjects pointed to targets at 90o (straight ahead), 60o and 120o on a circular arc of 0.15 m radius. In half of the trials, the target abruptly changed location at the onset of arm movement by 10 deg clockwise (CW) or counterclockwise (CCW) along the arc. After the baseline block, the V and W groups then performed a learning block, during which a mirror-image transform was applied along the 90o axis, so that a target at 60o required a reach to 120o, and vice versa. No target jumps were presented during the learning block. The V and W groups then did the test block, including target-jump trials, with the visuomotor transformation. In contrast, group C subjects never experienced the visuomotor transformation and did not perform the learning block. During their test block they were asked to “correct” their reach trajectory in the opposite direction to the target jump (c.f. Day & Lyon, 2000). Subjects in V group saw cursor feedback of hand position throughout all trials. Subjects in W and C groups received no cursor feedback during the movements. Instead, the final hand position relative to the target was displayed at the end of the trials without target jumps. Hand trajectory was captured by a digitizing tablet (100Hz) and analysed offline.
Results: During their test block, C group subjects initially moved in the direction of the target jump at the same short latency seen in their baseline block. They then reversed direction to move opposite to the target jump 100 - 200 msec later consistent with the findings of Day & Lyon (2000). V and W group subjects showed the same behaviour when reaching toward the 90o target. However, for the 60o and 120o targets, they suppressed the short-latency non-mirror responses to the target jump and only made the delayed mirror-transformed corrections.
Conclusion: These results suggest that short periods of practice with a mirror-image visuomotor transformation result in the suppression of the rapid online correction mechanism not its adaptation. Furthermore, the suppression only occurs for the movements in which the transformation was experienced. The presence or absence of real-time visual feedback of arm motion had no significant effect. |
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