研究目的：從過去的研究發現當受試者執行連續視覺動作任務時，特別是對於年輕人，給予錯誤量放大的視覺回饋可以使任務表現變好。然而，對於老年人來說，錯誤量放大的回饋帶來更多的訊息，可能會對他們退化的視覺動作系統造成超載，尤其是對老人偵測和快速處理錯誤是很大的挑戰。本研究想探討是否當老年人執行連續力量追蹤任務時，錯誤放大與低頻錯誤對於任務表現的影響。
研究方法：本研究共收取16位年長的健康受試者(平均年齡65.0 ± 3.2歲，7位男性，9位女性)，此任務需要他們用食指向外側壓完成20%最大自主收縮強度的靜態等長收縮，所有受試者都會完成四種由不同視覺引導的力量追蹤任務，分別為真實全域回饋(RF-FS)、真實低頻回饋(RF-LF)、錯誤放大(EA-FS)、錯誤放大的低頻回饋(EA-LF)。EA-FS和EA-LF分別會在低於0.4赫茲的低頻執行錯誤乘以兩倍的執行錯誤，RF-LF則會顯示沒有放大且僅提供低於0.4赫茲低頻執行錯誤，RF-FS則提供真實執行錯誤大小的視覺回饋。比較不同視覺回饋造成力量變異(force fluctuations)的均方根(root mean square,RMS) 、平均頻率(mean frequency, MF) 、樣本熵（sample entropy, SampEn）、和自由度(spectral degree of freedom, DOF)的差異。除此之外，背側第一骨間肌內的肌肉間相關性會用小偵測範圍的五針表面肌電圖收取資料，經全波整流後分析肌肉內的共調頻譜(intramuscular coherence)。實驗使用兩因子重複測量變異數分析檢測錯誤頻域(低頻和全頻的比較)和錯誤放大(錯誤放大和真實回饋的比較)對於力量變異和肌電圖的特徵差異。
研究結果：力量變異的結構受到回饋錯誤放大與錯誤頻域的影響。力量變異的均方根受到錯誤頻域而非錯誤放大的影響；兩種低頻錯誤回饋(RF-LF和EA-LF) 相對於全域回饋(RF-FS和EA-FS)有較大力量變異的均方根值。力量變異的平均頻率受到錯誤放大而非錯誤頻域的影響；力量變異的平均頻率在錯誤放大情形(EA-FS和EA-LF)較RF-FS和RF-LF出現較高的平均頻率。力量變異的樣本熵同時受到錯誤放大與錯誤頻域的影響；錯誤放大情形(EA-FS和EA-LF)樣本熵大於RF-FS和RF-LF的樣本熵。低頻錯誤回饋(RF-LF和EA-LF)的樣本熵大於全域錯誤回饋(RF-FS和EA-FS)的樣本熵。不論是錯誤頻域或錯誤放大在自由度方面都沒有造成顯著差異。相較於全域錯誤回饋，低頻錯誤回饋(RF-LF和EA-LF)在0-3赫茲有較高的肌內共調頻譜(intramuscular coherence)尖峰值。
結論：錯誤放大的視覺反饋並未如預期地改善老年人的力量穩定性。不論是否將錯誤放大，提供低頻執行錯誤的視覺回饋反而破壞年長者在連續視覺活動力量的穩定，可能涉及0-3Hz低頻肌肉振盪控制的調控增強有關。

Objectives: Error amplification (EA) feedback has been previously shown to improve quality of continuous visuomotor tasks, particularly for young adults. However, EA feedback enlarges error information that may overload visuomotor system of the elderly, who suffer from age-related decline in capacity of detection and processing of fast execution errors. This study examined whether older adults could benefit from visual feedback with amplification of low-frequency errors and/or preclusion of fast execution errors during a continuous force-tracking task.
Methods: Sixteen healthy older adults (age = 65.0 ± 3.2 years, 7 males, 9 females) completed static isometric force at 20% of maximal voluntary contraction through index abduction under four various visual guidance, including real feedback of full spectrum (RF-FS), low-frequency feedback without amplification (RF-LF), error amplification of full spectrum (EA-FS), and low-frequency feedback with amplification (EA-LF). EA-FS and EA-LF multiplied twice of full-spectrum execution errors and low-frequency execution errors under 0.4 Hz, respectively. RF-LF provided low-frequency execution errors under 0.4 Hz without error amplification. RF-FS was a control visual feedback of true error size with full spectrum. Root mean square (RMS), mean frequency (MF), sample entropy (SampEn), and spectral degree of freedom (DOF) of force fluctuations were featured. In addition, intramuscular coherence of the first dorsal interosseous muscle was characterized with a special 5-pin surface electromyography following rectification. Two-way repeated measured ANOVA was used to examine the effects of error spectrum (low-frequency vs. full spectrum) and error amplification (EA vs. RF) on variables of force fluctuations and EMG.
Results: Force fluctuation structures were selectively altered with error amplification and spectrum of motor errors. RMS of force fluctuations was tuned to main effect of error spectrum rather than error amplification. Visual feedback of low-frequency error (both RF-LF and EA-LF) led to larger than their counterparts (RF-FS and EA-FS). MF was a function of error amplification rather than error spectrum with larger MF of force fluctuations for EA-FS and EA-LF than that of the RF-FS and RF-LF. SampEn of force fluctuations was also subject to joint effects of error spectrum and error amplification. EA-FS and EA-LF had larger value than RF-FS and RF-LF did. However, RF-LF and EA-LF exhibited smaller than RF-FS and EA-FS did. DOF was not significantly different in error spectrum and error amplification. Low-frequency error feedback associated with larger EMG-EMG coherence peak at 0-3 Hz, whereas RF-FS and EA-FS led to lower coherence peak at 0-3 Hz.
Conclusion: Contrary to expectations, visual feedback with EA did not effectively improve force steadiness of the elderly. In addition, low-frequency error feedback with or without error amplification always undermined the force steadiness in the older group, pertaining to enhancement of low-frequency muscle oscillatory control at 0-3 Hz.

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