Castellini Claudio, Gruppioni Emanuele, Davalli Angelo, Sandini Giulio
LIRA-Lab, University of Genova, viale F. Causa 13, Genoa, Italy.
J Physiol Paris. 2009 Sep-Dec;103(3-5):255-62. doi: 10.1016/j.jphysparis.2009.08.008. Epub 2009 Aug 7.
The state-of-the-art feed-forward control of active hand prostheses is rather poor. Even dexterous, multi-fingered commercial prostheses are controlled via surface electromyography (EMG) in a way that enforces a few fixed grasping postures, or a very basic estimate of force. Control is not natural, meaning that the amputee must learn to associate, e.g., wrist flexion and hand closing. Nevertheless, recent literature indicates that much more information can be gathered from plain, old surface EMG. To check this issue, we have performed an experiment in which three amputees train a Support Vector Machine (SVM) using five commercially available EMG electrodes while asked to perform various grasping postures and forces with their phantom limbs. In agreement with recent neurological studies on cortical plasticity, we show that amputees operated decades ago can still produce distinct and stable signals for each posture and force. The SVM classifies the posture up to a precision of 95% and approximates the force with an error of as little as 7% of the signal range, sample-by-sample at 25Hz. These values are in line with results previously obtained by healthy subjects while feed-forward controlling a dexterous mechanical hand. We then conclude that our subjects could finely feed-forward control a dexterous prosthesis in both force and position, using standard EMG in a natural way, that is, using the phantom limb.
当前主动式假手的前馈控制技术相当落后。即使是灵巧的多指商业假手，也是通过表面肌电图（EMG）来控制的，其方式是强制采用几种固定的抓握姿势，或者是对力进行非常基本的估计。这种控制方式不自然，这意味着截肢者必须学会将例如手腕弯曲和手部闭合联系起来。然而，最近的文献表明，可以从普通的老式表面肌电图中收集到更多信息。为了验证这个问题，我们进行了一项实验，让三名截肢者使用五个市售的EMG电极训练支持向量机（SVM），同时要求他们用幻肢执行各种抓握姿势和力度。与最近关于皮质可塑性的神经学研究一致，我们表明，几十年前接受手术的截肢者仍然能够为每种姿势和力度产生独特且稳定的信号。SVM对姿势的分类精度高达95%，对力的近似误差小至信号范围的7%，在25Hz的频率下逐样本进行。这些值与健康受试者在对灵巧机械手进行前馈控制时先前获得的结果一致。然后我们得出结论，我们的受试者可以使用标准EMG以自然的方式，即使用幻肢，在力和位置上对灵巧假手进行精细的前馈控制。
