近年來，全世界手機使用的人口已逐漸增加，手機成為人們不可或缺的生活必需品之一，造成手機等通訊產品蓬勃發展，而手機除了通話的功能以外，文字簡訊的使用也逐漸受到歡迎，但輕薄短小的發展趨勢以及大螢幕的需求，加上多功能就是好的迷思，使得現有產品有多數皆不符合人因需求，尤其是按鍵越來越小，使得表面積較大的大拇指操作不易，近期有數位學者提出背面操作想法的研究，希望能發展出其他型態的操作方式，解決手機大小限制的難題。
本研究是以實體按鍵為主，探討新式手機背面操作方式之合適操作範圍以及水平按鍵間距，第一步先找出符合使用者人因需求之舒適操作範圍，第二步再根據第一步的結果範圍，在該範圍內配置不同水平間距的按鍵，以反應時間與錯誤率來探討何種間距較適合用於背面操作，並搭配心理量表的評估以及簡單的訪談，去了解背後的原因。期望能同時滿足使用者對產品的要求並兼顧符合人因需求的條件。
第一部分實驗進行以超過2/3受測者認為較好施力的範圍作為最後的結果，發現中指的移動範圍最大，小指及無名指的移動範圍較小，手長掌寬對於部份手指定位點X、Y值有顯著的影響，但以X值（水平方向）的影響較大。第二部份實驗請受測者操作四款不同按鍵間距的實驗模型，並使用電腦程式輔助測量反應時間與記錄錯誤次數，探討不同手指、不同間距兩個因子間的交互影響，結果發現12.5mm間距的反應時間最短，錯誤率也最低，並且各手指間適合的間距有些許差異，可作為日後發展背面操作按鍵的參考之一。

In recent years, people who use mobile phones are increasing worldwide. Mobile has become one of the necessities in our lives and results in thriving development of communication products, such as mobile phones. Besides communication, text message gradually becomes popular. The trends in thin and short mobile phones, the needs of large screen, and the myth of multi-function mobiles make most of the existing products hardly meet the demands of human factors. For instance, it is really hard to use large-surface thumb to press the smaller and smaller keys. To solve this problem, some scholars have researched into back-side operation and look forward to developing other operating ways.
In this study, we mainly focused on physical keys and discussed the proper operation range for backside operating function in modern mobile phones and the horizontal space between keys. First, we tried to find the operation range which fits demands of human factors and makes users feel comfortable. Second, the keys were arranged in different horizontal space within the range we measured. Third, based on the response time and error rate, we evaluated which space is more proper to use in backside operation. Meanwhile, we used a psychological assessment scale and some simple interviews to see the reasons behind.
In the first part of our experiment, we used the range which satisfies more than two thirds of subjects. Later, we found that the range for middle finger is the largest while the ranges for ring and little finger are relatively small. On the other hand, length and width of hands have significant impacts on the coordinates of finger location point, especially on X coordinates. In the second part, subjects operated four experimental models arranged in different key space. With the assistance of computer programs, we recorded the reaction time and error rate of each other. Therefore, we can evaluate the mutual effects between different fingers and key space. According to the data, we found the reaction time for 12.5mm space is the shortest one and it also has the lowest error rate. Although there is some difference in proper space for respective fingers, the results can be regarded as reference of backside keys operation in the future.

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網路資料
1. 資策會FIND網站：2009年第四季我國行動上網觀測http://www.find.org.tw/find/home.aspx?page=many&id=252