Paredes Liliana P, Dosen Strahinja, Rattay Frank, Graimann Bernhard, Farina Dario
Laboratorio di Cinematica e Robotica, Fondazione Ospedale San Camillo - I.R.C.C.S., Lido di Venezia, Italy.
Department of Neurorehabilitation Engineering, University Medical Center Goettingen, Goettingen, Germany.
J Neuroeng Rehabil. 2015 Apr 9;12:35. doi: 10.1186/s12984-015-0022-8.
Electrocutaneous stimulation can restore the missing sensory information to prosthetic users. In electrotactile feedback, the information about the prosthesis state is transmitted in the form of pulse trains. The stimulation frequency is an important parameter since it influences the data transmission rate over the feedback channel as well as the form of the elicited tactile sensations.
We evaluated the influence of the stimulation frequency on the subject's ability to utilize the feedback information during electrotactile closed-loop control. Ten healthy subjects performed a real-time compensatory tracking (standard test bench) of sinusoids and pseudorandom signals using either visual feedback (benchmark) or electrocutaneous feedback in seven conditions characterized by different combinations of the stimulation frequency (FSTIM) and tracking error sampling rate (FTE). The tracking error was transmitted using two concentric electrodes placed on the forearm. The quality of tracking was assessed using the Squared Pearson Correlation Coefficient (SPCC), the Normalized Root Mean Square Tracking Error (NRMSTE) and the time delay between the reference and generated trajectories (TDIO).
The results demonstrated that FSTIM was more important for the control performance than FTE. The quality of tracking deteriorated with a decrease in the stimulation frequency, SPCC and NRMSTE (mean) were 87.5% and 9.4% in the condition 100/100 (FTE/FSTIM), respectively, and deteriorated to 61.1% and 15.3% in 5/5, respectively, while the TDIO increased from 359.8 ms in 100/100 to 1009 ms in 5/5. However, the performance recovered when the tracking error sampled at a low rate was delivered using a high stimulation frequency (SPCC = 83.6%, NRMSTE = 10.3%, TDIO = 415.6 ms, in 5/100).
The likely reason for the performance decrease and recovery was that the stimulation frequency critically influenced the tactile perception quality and thereby the effective rate of information transfer through the feedback channel. The outcome of this study can facilitate the selection of optimal system parameters for somatosensory feedback in upper limb prostheses. The results imply that the feedback variables (e.g., grasping force) should be transmitted at relatively high frequencies of stimulation (>25 Hz), but that they can be sampled at much lower rates (e.g., 5 Hz).
电皮肤刺激可将缺失的感觉信息恢复给假肢使用者。在电触觉反馈中，有关假肢状态的信息以脉冲序列的形式传输。刺激频率是一个重要参数，因为它会影响反馈通道上的数据传输速率以及所引发的触觉感受形式。
我们评估了刺激频率对受试者在电触觉闭环控制期间利用反馈信息能力的影响。10名健康受试者在7种条件下，使用视觉反馈（基准）或电皮肤反馈对正弦波和伪随机信号进行实时补偿跟踪（标准测试台），这7种条件的特点是刺激频率（FSTIM）和跟踪误差采样率（FTE）的不同组合。跟踪误差通过放置在前臂上的两个同心电极进行传输。使用平方皮尔逊相关系数（SPCC）、归一化均方根跟踪误差（NRMSTE）以及参考轨迹和生成轨迹之间的时间延迟（TDIO）来评估跟踪质量。
结果表明，对于控制性能而言，FSTIM比FTE更重要。随着刺激频率降低，跟踪质量下降，在100/100（FTE/FSTIM）条件下，SPCC和NRMSTE（平均值）分别为87.5%和9.4%，而在5/5条件下分别降至61.1%和15.3%，同时TDIO从100/100条件下的359.8毫秒增加到5/5条件下的1009毫秒。然而，当以低速率采样的跟踪误差以高刺激频率传递时，性能得以恢复（在5/100条件下，SPCC = 83.6%，NRMSTE = 10.3%，TDIO = 415.6毫秒）。
性能下降和恢复的可能原因是刺激频率严重影响触觉感知质量，从而影响通过反馈通道的有效信息传递速率。本研究结果有助于为上肢假肢的体感反馈选择最佳系统参数。结果表明，反馈变量（如抓握力）应以相对较高的刺激频率（>25赫兹）进行传输，但可以以低得多的速率（如5赫兹）进行采样。
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