背景與目的：近期的研究結果顯示，站立平衡並非自動化的活動，而是一項需要注意力資源的作業。在注意力資源有限之前提下，許多學者利用雙重作業模式，探討同時作業與站立平衡之間的互動關係。過去之文獻顯示，站立平衡的表現會受到同時作業的困難度影響，然而此影響是正面的（增加站立穩定度）或反面的（降低站立穩定度）卻有不同結果。此外，過去研究在探討同時作業對站立平衡的影響時，他們所設計的同時作業之困難度層次不多，因此，本研究增加同時作業的困難度層次，以探討同時作業的困難度（注意力負荷）對站立平衡之影響。另外，也將探討此影響在年齡發展之效應。方法：本研究共有五個年齡族群的受試者參與：年輕成人與11~12歲、9~10歲、7~8歲、5~6歲的正常發展兒童。受試者執行在坐姿下之視覺搜尋測試、站立平衡測驗與同時執行視覺搜尋與站立平衡之雙重作業測試。視覺搜尋作業為卡通圖案的辨識，共有8種不同困難程度。統計分析採用重複量數變異數分析，探討年齡及視覺搜尋困難度對於站立平衡之影響。以壓力中心位移總路徑長、壓力中心前後及左右方向位移變異量為站立平衡參數，以視覺搜尋反應時間、正確率和複合C分數為視覺搜尋作業參數。站立平衡參數再以雙重作業虧損表示之（用雙重作業之值減掉單獨作業之值）。結果：視覺搜尋作業的表現（反應時間、正確率及複合C分數）具有年齡的主要效應（但並非兩兩年齡間皆有顯著差異），也反應困難度之差異（卡通圖案個數變多時，反應時間會隨之增加，複合C分數會隨之減少）。站立平衡的表現上，沒有年齡的差異，視覺搜尋困難度作業的效應也只在呈現於壓力中心左右位移之變異量（總路徑長和前後位移變異程度的雙重作業虧損皆無法反應困難度的差異）。除5~6歲外，其餘年齡層的左右位移變異量之雙重作業虧損值皆為負值，亦即表示雙重作業時站立穩定度變好。結論：雙重作業下，視覺搜尋作業的確是會造成站立平衡穩定度的影響，此影響會增進年輕成人與7~12歲兒童之站立平衡控制之表現，但卻會降低5~6歲兒童之站立平衡控制之表現，但視覺搜尋作業對站立平衡之影響並不受到作業困難度的影響。不同年齡的發展趨勢只在視覺搜尋作業表現上有顯現出，但卻沒有在站立平衡穩定度受覺搜尋同時作業的影響上顯示出，顯示兒童在處理視覺搜尋與站立平衡控制的同時作業之能力，可能在7~8歲就已發展到年輕成人的程度。

Background and Purpose: Results of recent studies showed that standing postural control was not automatic, but required central processing resources. Based on the premise that the central processing resources are limited, many researchers adopted a dual–task paradigm to investigate the interaction between the performance from concurrent task and standing stability. Results of the previous studies have demonstrated that the effect of a concurrent task on standing balance depended on the difficulty levels of the concurrent task. However, they are inconsistent in whether a concurrent task would facilitate or deteriorate standing stability. Moreover, the difficulty levels of a concurrent task were previously manipulated limited. The purpose of the study was to investigate the effect of a concurrent visual search task on standing stability while manipulating the difficulty levels over a wide range. The specific aims were to examine if the effect of a concurrent visual search task on standing stability would be dependent on the difficulty levels of the visual search task and if such an effect has displayed a developmental trend. Methods: Subjects of 5 age groups participated in the study: young adults, children of 11~12, 9~10, 7~8 and 5~6 years old. Participants performed the following tasks: single visual search task while seated, single standing stability task and dual-task in which participants performed a visual search task while maintaining standing stability. The visual search task required that the participants searched for a target among a set of cartoon pictures. There were 8 difficulty levels. The difficulty level was manipulated by the size of the set to be search for. The main effects of difficulty level of visual search task and age were examined using repeated measures ANOVA. Dual-task cost of center of pressure (COP) path length, dual-task cost of COP variability at anterior-posterior (AP) and medial-lateral (ML) directions, reaction time (RT), correct rate (CR) and composite score define were collected and used as dependent variables. Results: There was a main effect of age on RT, CR and composite score. As the set size increased, the RT increased and the composite score decreased. There was a main effect of set size on dual-task cost of COP variability at the ML direction. In adults, 11~12 years old, 9~10 years old, and 7~8 years old , standing stability increased at the ML direction in the dual task condition. Conclusion: Standing stability was facilitated by a concurrent visual search task in young adults and 7~12 years old children, but deteriorated in 5~6 years old children. The facilitation effect of standing stability is not affected by the difficulty levels of the visual search task. The effect of developmental trend was only found in the performance of visual search task, but not in the performance of standing stability. It implies that the children of 7~8 years old may have developed the ability of integrating the dual-task of visual search task and standing stability to the same level as young adults.

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