Department of Kinesiology, The Pennsylvania State University, Rec. Hall-267, University Park, PA 16802, USA.
Exp Brain Res. 2013 May;226(4):565-73. doi: 10.1007/s00221-013-3469-5. Epub 2013 Mar 15.
We studied a mechanism of feed-forward control of a multi-finger action, namely anticipatory synergy adjustments (ASAs), prior to a quick force correction in response to a change in the gain of the visual feedback. Synergies were defined as co-varied across trials adjustments of commands to fingers that stabilized (decreased variance of) the total force. We hypothesized that ASAs would be highly sensitive to prior information about the timing of the action but not to information on its direction, i.e., on whether the gain would go up or down. The subjects produced accurate constant total force by pressing with four fingers on individual force sensors. The feedback signal could change from veridical (the sum of finger forces) to modified, with the middle finger force multiplied by 0.2 or by 1.8. The timing of the gain change and its direction could be known or unknown to the subject in advance. When the timing of the gain change was known, ASA was seen as a drop in the synergy index starting about 250-300 ms prior to the first visible correction of the total force. When the gain change timing was unknown, ASAs started much later, less than 100 ms prior to the total force correction. The magnitude of synergy index changes was significantly larger under the "time known" conditions. Information on the direction of the visual gain change had no effect on the ASA timing, while the ASA magnitude was somewhat larger when this information was not available to the subject. After the total force correction, the synergy index was significantly larger for the force signal computed using the modified gain values as compared to the synergy index value for the actual total force. We conclude that ASAs represent an important feed-forward motor control mechanism that allows preparing for a quick action even when the direction of the action is not known in advance. The results emphasize the subtle control of multi-finger synergies that are specific to the exact contributions of individual fingers to performance variables. The data fit well the central back-coupling hypothesis of synergies and the idea of control with referent body configurations.
我们研究了多手指动作前馈控制的一种机制，即预期协同调整（ASAs），以便在视觉反馈增益变化时快速进行力校正。协同作用被定义为在试验中手指的命令协同变化，以稳定（降低总力方差）总力。我们假设 ASAs 对动作时间的先验信息非常敏感，但对其方向的信息不敏感，即增益是增加还是减少。受试者通过用四个手指按压单个力传感器来产生准确的恒定总力。反馈信号可以从真实（手指力的总和）变为修改后的信号，其中中间手指力乘以 0.2 或 1.8。增益变化的时间和方向可以事先让受试者知道或不知道。当增益变化的时间已知时，ASAs 表现为协同指数的下降，大约在第一个可见的总力校正之前 250-300 毫秒开始。当增益变化时间未知时，ASAs 开始得晚得多，在总力校正之前不到 100 毫秒。在“时间已知”条件下，协同指数变化的幅度明显更大。视觉增益变化方向的信息对 ASA 时间没有影响，而当受试者无法获得此信息时，ASA 的幅度会略大。在总力校正后，使用修改后的增益值计算的力信号的协同指数明显大于实际总力的协同指数值。我们得出结论，ASAs 代表了一种重要的前馈运动控制机制，即使在事先不知道动作方向的情况下，也可以为快速动作做准备。结果强调了对特定于个体手指对性能变量的精确贡献的多手指协同作用的微妙控制。该数据非常符合协同作用的中央后耦合假设和参照身体构型的控制思想。
