| Summary: | 博士 === 國立臺灣大學 === 職業醫學與工業衛生研究所 === 97 === 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.
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