Experimental Study On The Mental Workload Evaluation During Performance On VDT

Along with the development of computer technology, information industry will become a reality in the near future. VDT has broad application in many fields. People will be increasingly tied to various computer terminals in work, life and learning. The proportion of physical work in the society is gradually decreasing, meanwhile the proportion of mental work is gradually increasing, more people are engaged in complicated mental work with VDT. The amount of information that the operators need to dealing is constantly increasing, so that the requirements of information processing is often exceed to our cognitive ability. So how to assess the operator's mental workload, have more and more important meanings in the area of occupational health.Back in the 20th century, the early 1970s, industrial countries have begon to recognize the importance of evaluating mental work load, and put a lot of human and financial resources on the research of mental work. Some significant developments are achived, such as the subjective method of Cooper-Harper scale, changes in pupil size, heart rate variability, Event Related Potention as the objective measurements. Mental workload is a multidimensional concept, which involves work, time pressure, the ability and efforts of operators, performance and many other factors. The factor affecting mental workload are very complex, and there are many uncertainties factor, it is difficult to use a single standard to measure. At the present time, there have no method can assessment the mental workload accurately. There are some research on the mental workload evaluation in the world, but there haven't systemic research on the mental workload evaluation during performance on VDT. So we use subjective rate, primary task evaluation and psychophysiology evaluation as methods to assessment mental workload during reading performance on VDT. Main research as following: Firstly, Compare the mental workload evaluation during reading performance on VDT. Secondly, Compare the mental workload between three different difficult mental arithmetic on VDT. Thirdly, Compare the mental workload between different time performance on VDT, explore work-rest schedule of VDT task. Fourthly, Comparison of mental workload between VDT and paper-based reading. Fifthly, application of heart rate variability in evaluation of mental workload during performance on VDT.Part one Experimental study on the mental workload evaluation during reading performance on VDTObjective To investigation the possibility of subjective rate, primary task evaluation and psychophysiology evaluation as methods for mental workload evaluation during reading performance on VDT.Methods 14 student volunteers as subjects were divided into three group as A,B,C group and required to read short papers and answer questions on the computer for 15, 30 and 60 minutes. Parameters including Cooper-Harper scale score, correct rate, reading speed, reading efficiency, heart rate variability, pupil size, blink rate were determined.Results With the time increasing, the Cooper-Harper scale score, the right rate, the speed, pupil size and blink rate weren't significantly different among three group. Reading efficiency of C group decreased compared to A group; In comparison with rest, the value of TP,VLF,LF,HF,SDNN increased remarkably, the value of TB decreased, however, the difference weren't significantly among three group. Conclusions Reading of VDT have certain effect on participant's mental workload in 60 minutes. Three mental workload evaluation methods can assessed the mental work load information during reading performance on VDT in a way, can used to assess mental workload.Part Two Experimental study on the mental workload evaluation during mental arithmetic on VDTObjective To investigation the possibility of subjective rate, primary task evaluation and psychophysiology evaluation as methods for mental workload assessment in mental arithmetic of VDT.Methods The indexes including Cooper-Harper scale score , correct rate, speed in answering questions, heart rate variability, pupil size, blink rate were recorded during performance of three different difficult task.Results With the difficulty increasing, the Cooper-Harper scale score increased, the right rate decreased,the speed decreased, pupil size increased, blink rate were significantly decreased. In comparison with rest, the value of TP,VLF,LF,LFnorm,LF/HF decreased remarkably in the mental arithmetic work, the value of HFnorm,HF/TP,RRA,rMSSD increased, however, the difference weren't significantly among three different difficult task.Conclusions Every indexes can effected the mental work load information in three different difficult task in a way, multi-indexes may be preferred for mental load assessment.Part Three Experimental study on the work-rest schedule of VDT taskObjective To investigate the work-rest schedule on different type of VDT task.Methods 14 student volunteers as subjects were required to read short articles and answer questions on the computer for 15, 30 and 60 minutes. Parameters including Cooper-Harper scale score, correct rate, reading speed, reading efficiency, RPE score were determined. 46 student volunteers as subjects were required to enter random data into computer for 60 minutes. Parameters including correct rate, data-entry speed were determined every 10 minutes.Results With increasing of the performance time, the Cooper-Harper scale score, the right rate, reading speed, RPE score didn't show any significant changes. However, the efficiency of reading for 60 minutes decreased significantly as compared with that of 15 minute reading. With the increase of lasting time, the data-entry speed were increased, the right rate have decrease tendency, but the difference weren't significantly.Conclusions It demonstrated that reading efficiency were decreased after continuing reading over the screen computer for 60min, but the data-entry speed were increased. It is suggested that participant's performance with different change rule on different type of VDT task, should setting different work-rest schedule.Part Four Comparison of mental workload between VDT and paper-based readingObjective Comparison of mental workload between VDT and paper-based reading measured by subjective rate, primary task evaluation and psychophysiology evaluation methods.Methods The indexes including Cooper-Harper scale score , correct rate, speed in answering questions, reading efficiency, heart rate variability, pupil size, blink rate were recorded during performance of VDT and paper-based reading task.Results The Cooper-Harper scale score, the right rate, the speed, reading efficiency, HRV, pupil size and blink rate weren't significantly different between VDT and paper-based reading. In comparison with rest, blink rate decreased, the value of TP,LF,HF,SDNN increased remarkably during VDT and paper-based reading, the value of VLF increased during VDT-based reading.Conclusions It demonstrated that participant's mental workload weren't significantly different in 30 minutes between VDT and paper-based reading. Three mental workload evaluation methods can assessed the mental work load information during reading performance on VDT in a way, can used to assess mental workload.Part Five Application of heart rate variability In evalualton of mental workload during performance om VDTObjective Observing Heart rate variability in VDT task in order to evaluate the mental workload of volunteers by the parameter.Methods volunteers do the tasks which are given by computer, and we record their continuous ECG signals by Holter 8800. Volunteers give subjective evaluation about mental workload by answer Cooper-Harper scale, multistage evaluation scale (MES) and Borg scale.Results The mental workload is changed in the different VDT tasks. There has a significant difference of HRV between mental arithmetic task and the rest. However, only TP of HRV has a significant change between reading task and the rest. HRV has no significant change in several task Difficulty.Conclusion HRV can be a physiological index to evaluate mental workload. But the mechanics and relationship of dose-reaction with mental workload still deserve further study.