Differential control of task and null space variability in response to changes in task difficulty when learning a bimanual steering task
Differential control of task and null space variability in response to changes in task difficulty when learning a bimanual steering task
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DOI：
10.1007/s00221-019-05486-2
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发表时间：
2019-04-01
影响因子：
2
通讯作者：
Ranganathan, Rajiv
中科院分区：
文献类型：
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作者：
Lokesh, Rakshith;Ranganathan, Rajiv
运动冗余的存在意味着运动可变性可以分为影响任务性能的“任务空间”组件和对任务性能没有影响的“零空间”组件。虽然在学习过程中对任务空间可变性的控制是必不可少的，因为它与表现直接相关，但神经系统在学习过程中如何控制零空间可变性尚未得到很好的理解。一个被假设控制零空间可变性随学习变化的因素是任务难度，但这还没有被直接测试。在这里，我们研究了任务难度如何影响零空间可变性随学习的变化。健康的、大学年龄的参与者（N = 36）执行了一项双手操纵任务，他们在尽可能快地操纵光标通过一条一定宽度的光滑w形轨迹，同时试图将光标保持在轨迹内。通过改变赛道宽度来改变任务难度，参与者根据他们练习的赛道宽度分为三组：宽、窄或渐进（赛道的宽度在练习中逐渐从宽变窄）。这个任务的冗余源于这样一个事实，即光标的位置被定义为两只手的平均位置。结果表明，运动时间与任务难度有关，但所有组都能随着练习而减少运动时间。在所有组中，学习都与零空间变异性的降低有关，但关键的是，任务难度没有影响。进一步的分析表明，虽然任务空间可变性显示了预期的速度-精度与移动时间的权衡，但零空间可变性显示了一种质的不同模式。这些结果表明，随着学习任务难度的变化，任务和零空间可变性的差异控制可能反映了学习过程中最小化整体运动可变性的强烈偏好。
The presence of motor redundancy means that movement variability can be split into a 'task-space' component that affects task performance, and a 'null space' component which has no effect on task performance. While the control of task-space variability during learning is essential, because it is directly linked to performance, how the nervous system controls null space variability during learning has not been well understood. One factor that has been hypothesized to govern the change in null space variability with learning is task difficulty, but this has not been directly tested. Here, we examined how task difficulty influences the change in null space variability with learning. Healthy, college-aged participants (N = 36) performed a bimanual steering task, where they steered a cursor through a smooth W-shaped track of a certain width as quickly as possible while attempting to keep the cursor within the track. Task difficulty was altered by changing the track width and participants were split into one of the three groups based on the track width that they practiced on-wide, narrow, or progressive (where the width of the track progressively changed from wide to narrow over practice). The redundancy in this task arose from the fact that the position of the cursor was defined as the average position of the two hands. Results showed that movement time depended on task difficulty, but all groups were able to decrease their movement time with practice. Learning was associated with a reduction in null space variability in all groups, but critically, there was no effect of task difficulty. Further analyses showed that while the task-space variability showed an expected speed-accuracy tradeoff with movement time, the null space variability showed a qualitatively different pattern. These results suggest differential control of task and null space variability in response to changes in task difficulty with learning, and may reflect a strong preference to minimize overall movement variability during learning.