以打字擊鍵特性與心跳變異率探討影響打字表現之因子

Abstract

電腦是現代人工作與生活中不可或缺的工具，在電腦應用普遍的同時，長時間使用是否會造成健康危害更加值得重視。打字是使用電腦時重要的活動之一，過去針對繕打(transcription typing)的研究顯示，它牽涉到視覺接收、大腦訊息處理、動作計畫、以及轉換成快速的兩側手指活動等複雜過程，如此高重複性、且常常持續數小時的活動，很可能造成相當的生理心理負荷。 針對從事電腦作業的生理負荷，過去的研究包括使用表面肌電圖，測量上肢與斜方肌的疲勞狀況；而壓力或情緒方面的負荷，則有部分研究使用心跳、心跳變異率( heart rate variability, HRV)、腦波、尿液中的腎上腺素、或者electrodermal activity (EDA)等方法來了解受試者的壓力或疲勞狀況。這些關於重複性活動或資料輸入的研究結果並不一致，部分研究認為這些活動可能引起心理疲勞、大腦皮質覺醒減少，而使資料輸入時的工作表現隨時間而降低；另一些研究則認為為了能夠維持專注，反而可能由心跳變異率的改變反映出心理壓力。上述的生理心理變化，可能直接或間接造成打字者的健康效應。綜觀過去研究，少有針對使用電討鍵盤連續繕打之報告，若能利用不同評估工具，探討電腦作業時疲勞發生的時序性與影響因子，將有助於建立以實證為基礎的安全衛生指引，給予電腦工作者適切的建議。 本研究之目的在於探討觀察使用電腦鍵盤連續繕打過程中，以電子活動監測軟體所測得之擊鍵間隔變化能否反映打字者工作表現變化或疲勞之發生，並與其他工具之評估結果相互比對，包括：自覺症狀、打字表現（打字軟體測得之字數）、心跳以及心跳變異率。此外，並探討電腦使用者常見的習慣&not;--聆聽音樂—對於打字中生理反應與打字表現之影響。 第一個子研究中，24位受試者進行連續三段30分鐘的英文打字，利用電子活動監測軟體紀錄其過程中雙手擊鍵間隔的變化，並探討其影響因子。研究結果發現，左右手之擊鍵間隔在過程中有不同的變化趨勢，左手的擊鍵間隔隨時間逐漸延長，在每次三十分鐘的初始的第三個十分鐘有較長的擊鍵間隔 (β=3.4, p<0.0001)，且右手的擊鍵間隔在最後的十分鐘有明顯縮短 (β=－3.7, p<0.01)，顯示左右手在打字過程中可能有不同的疲勞傾向。 第二個子研究比較使用不同中文打輸入法打字的差異，以方便取樣法選取十六位自願者，九位使用微軟新注音輸入中文，七位使用嘸蝦米輸入中文，兩組英文打字速度相近，以重複測量方式，分別觀察使用英文及中文連續繕打三十分鐘之手部動作表現，分析使用的鍵分布頻率，以及雙手與各手指的使用頻率，並且利用GEE統計模式分析重覆測量之數據，了解不同打字法以及中英文打字等因素對於擊鍵間隔的影響。結果發現，兩種中文輸入法的左右手使用頻率較英文打字法平均，微軟新注音使用較多的數字排（number row）；GEE分析結果顯示，使用嘸蝦米打字法，擊鍵間隔最短 (β=－26.3, p<0.0001)，英文打字則較中文打字有較長的擊鍵間隔 (β=16.5, p<0.0001)。 第三個子研究觀察連續英文繕打九十分鐘時，四十三位受試者心跳與心跳變異率隨時間的變化，並隨機分配受試者於打字時聽音樂與否，比較兩組之打字表現、自覺疲勞、心跳以及心跳變異率的差異；結果顯示，聽音樂與否並不影響整體打字速度或自覺疲勞；心跳變異率(lnHF與SDNN)分別在打字活動前40與20分鐘減少，而心跳在前六十分鐘高於後三十分鐘。此外，聽音樂組的心跳變異率(lnHF與SDNN)也顯著較低，不過若是原有聽音樂習慣，則聽音樂不影響心跳變異率。此結果顯示，打字為一智能活動，會造成心理壓力、且表現在心跳變異率的降低，與過去研究相符，然而，受試者在持續40分鐘以上的打字活動，疲勞產生，心跳變異率回昇、心跳變慢。本研究顯示聽音樂並不影響打字表現與自覺症狀，但減少心跳變異率，暗示可能的覺醒或壓力效應，然而，習慣聽音樂者並不受影響。 總結，連續九十分鐘的電腦鍵盤繕打可能造成心理與生理的負荷，擊鍵間隔的分析顯示左右手變化的明顯差異；而不同的中英文輸入法影響受試者的擊鍵間隔以及各個位置或不同手指的擊鍵頻率；心跳變異率與心跳的改變顯示連續打字為一智能活動，但超過四十分鐘就可能產生疲勞；聽音樂可能減低心跳變異率，對受試者產生警醒或壓力效果，但在習慣聽音樂者則無此效應。上述研究結果有助於研究者更清楚不同打字狀況下的生理反應以及影響因子，對於探討電腦工作者的健康危害與制定安全衛生指引，提供重要的科學證據。

Computers are widely used for working and recreation in modern life and the related health hazards are of concerns since a great number of population are exposed to long-term computer operation in workplaces and daily living. Transcription typing is one of the important parts of computer tasks and involves complex visual perception, information processing, motor planning and fast motor execution by fingers. Sustained typing should therefore attribute to psychophysiological loading to the individuals. For the physical loading during continuous working with computers, many researches applied surface electromyography to investigate the muscular fatigue of trapezius and other muscles at upper limbs. Meanwhile, for the psychological or mental response, several measures have been used for repetitive or data entry tasks, including heart rate, heart rate variability, electroencephalography (EEG), urinary adrenaline and electrodermal activity. Nevertheless, these aforementioned studies showed inconsistent results. Some studies demonstrated deteriorated work performance with time, suggesting accumulating mental fatigue and reduced cerebral arousal after prolonged data entry tasks. In contrast, other studies found that computer tasks required sustained attention and were associated psychological stress as other mental-demanding tasks. The psychophysiological response was reflected by the increased heart rate and reduced heart rate variability. The above findings implied that sustained computer work would combine the characteristics of vigilance tasks and repetitive ones, and the psychophysiological changes over time should reveal both decrement in the arousal level and compensatory adjustment to the job demands. Moreover, the above psychophysiological response could cause health hazards. It is therefore important to describe the temporal change and investigate the determinants, in order to provide evidence-based strategies for health promotion for the computer users. The goal of the current research was to explore whether the parameters recorded by the electronic activity monitoring software are applicable to reflect the temporal change of work productivity or development of fatigue during continuous transcription typing with computer keyboards. The relationship between these parameters and other measurements, such as self-reported symptoms, typing words, heart rate and heart rate variability, were also investigated. Besides, we investigated the effect of a common habit, music listening, on typing performance and the psychophyioslogical measures. In the first study, 24 subjects typed English for 90 minutes with one-minute break between every two consecutive 30-minute sessions. IKIs were computed and analyzed for each hand and the influence of personal and typing-related factors was explored. The results showed a different trend of IKIs for both hands, that is, IKIs of left hand would prolong as the task continued and IKIs in the third 10-minute period of every 30-minute session was prolonged (β=3.4, p<0.0001). Besides, a significant shortening of right-hand IKIs in the last 10-minute period (β=－3.7, p<0.01) was consistent with the rebound phenomenon found by previous studies. Different motor loading and dexterity of two hands would likely contribute to the different trend of change. The utility and typing characteristics of two Chinese-input methods by keyboards were investigated in the second study. A convenient sample of 16 subjects with similar English-typing speed was enrolled. They used either Boshiamy (7 subjects) or Microsoft New Phonetic method (9 subjects) for typing Chinese. All the subjects typed English and Chinese for 30 minutes respectively in two occasions of tests. IKIs and key frequency according to fingers and keyboard positions were analyzed by generalized estimating equations (GEE) method. The results showed that Chinese-typing with either method had a more equalized hand loading than English-typing which presented a higher left-hand loading. Microsoft New Phonetic used more keys at number row than Boshiamy and English-typing. GEE analysis showed that transcription typing with English are associated with longer IKIs than Chinese typing (β=16.5, p<0.0001), and typing with Boshiamy had significantly shorter IKIs than the other two methods (β=－26.3, p<0.0001). The third study observed the change of heart rate and heart rate variability (HRV) during a continuous English-typing for 90 minutes. 43 conveniently sampled participants were randomized into two groups with music listening or none during typing. The results showed that music and no-music groups had similar overall typing speed and self-perceived fatigue. LnHF (natural logarism of high frequency) and standard deviation of heart rate (SDNN) were reduced in the first 40 and 20 minutes of typing and heart rate in the first one hour was significantly higher than that at the late 30 minutes. Music listening was also associated with a reduced HRV (lnHF and SDNN). Nevertheless, there was no reduction of HRV when the subjects had the habit of music-listening in music group. The results support that typing is a mental task and associated with psychophysiological stress, which is reflected by reduced heart rate variability and increased heart rate. However, after 40-minute typing task, heart rate variability increases and heart rate slows down, which implies the effect of mental fatigue. Music-listening do not influence typing performance and self-perceived fatigue, but might still impose an arousal or strain effect, which is dependent on the habit of music-listening. In conclusion, sustained transcription typing with computer keyboards for 90 minutes may cause psychophysiological loading. The discriminating temporal change in typing performance of two hands is well documented by the analysis in IKIs. Different input methods also influence the hand loading and IKIs. The reduction in HRV and increase in heart rate supports that typing is a mental task, but mental fatigue develops after 40 minutes. Music listening is associated with reduced HRV and brings arousal or strain effect, but the effect is not seen among subjects with habit of music listening during typing. Our results clarify the psychophysiological change during transcription typing and the determinants of the above change. They provide important evidence for further research on the health effect and the development of preventive strategies for computer-related health hazards.