Northwestern University and the Shirley Ryan AbilityLab, Chicago, IL, USA.
Fondazione Istituto Italiano di Tecnologia, Genoa, Italy.
J Neuroeng Rehabil. 2020 May 11;17(1):61. doi: 10.1186/s12984-020-00681-7.
Body-machine interfaces map movements onto commands to external devices. Redundant motion signals derived from inertial sensors are mapped onto lower-dimensional device commands. Then, the device users face two problems, a) the structural problem of understanding the operation of the interface and b) the performance problem of controlling the external device with high efficiency. We hypothesize that these problems, while being distinct are connected in that aligning the space of body movements with the space encoded by the interface, i.e. solving the structural problem, facilitates redundancy resolution towards increasing efficiency, i.e. solving the performance problem.
Twenty unimpaired volunteers practiced controlling the movement of a computer cursor by moving their arms. Eight signals from four inertial sensors were mapped onto the two cursor's coordinates on a screen. The mapping matrix was initialized by asking each user to perform free-form spontaneous upper-limb motions and deriving the two main principal components of the motion signals. Participants engaged in a reaching task for 18 min, followed by a tracking task. One group of 10 participants practiced with the same mapping throughout the experiment, while the other 10 with an adaptive mapping that was iteratively updated by recalculating the principal components based on ongoing movements.
Participants quickly reduced reaching time while also learning to distribute most movement variance over two dimensions. Participants with the fixed mapping distributed movement variance over a subspace that did not match the potent subspace defined by the interface map. In contrast, participant with the adaptive map reduced the difference between the two subspaces, resulting in a smaller amount of arm motions distributed over the null space of the interface map. This, in turn, enhanced movement efficiency without impairing generalization from reaching to tracking.
Aligning the potent subspace encoded by the interface map to the user's movement subspace guides redundancy resolution towards increasing movement efficiency, with implications for controlling assistive devices. In contrast, in the pursuit of rehabilitative goals, results would suggest that the interface must change to drive the statistics of user's motions away from the established pattern and toward the engagement of movements to be recovered.
ClinicalTrials.gov, NCT01608438, Registered 16 April 2012.
人机接口将运动映射到外部设备的命令上。从惯性传感器中获得的冗余运动信号被映射到低维设备命令上。然后，设备用户面临两个问题，a）理解接口操作的结构问题，b）高效控制外部设备的性能问题。我们假设这些问题虽然不同，但存在联系，即通过将身体运动的空间与接口编码的空间对齐，解决结构问题，有助于通过提高效率来解决冗余问题。
20 名未受损的志愿者通过移动手臂来练习控制计算机光标移动。四个惯性传感器的八个信号被映射到屏幕上的两个光标坐标上。映射矩阵通过要求每个用户执行自由形式的自发上肢运动并得出运动信号的两个主要主成分来初始化。参与者进行了 18 分钟的到达任务，然后进行跟踪任务。一组 10 名参与者在整个实验中使用相同的映射进行练习，而另一组 10 名参与者则使用迭代更新的自适应映射，根据正在进行的运动重新计算主成分。
参与者很快减少了到达时间，同时也学会了将大部分运动方差分布在两个维度上。使用固定映射的参与者将运动方差分布在与接口映射定义的有效子空间不匹配的子空间中。相比之下，使用自适应映射的参与者减少了两个子空间之间的差异，从而减少了分布在接口映射零空间上的手臂运动。这反过来又提高了运动效率，而不会影响从到达到跟踪的泛化。
将接口映射定义的有效子空间与用户的运动子空间对齐，可以指导冗余问题的解决，从而提高运动效率，这对控制辅助设备具有重要意义。相比之下，在追求康复目标的过程中，结果表明，为了驱动用户运动的统计数据远离既定模式并朝着需要恢复的运动的参与，接口必须改变。
ClinicalTrials.gov，NCT01608438，2012 年 4 月 16 日注册。
