The Japanese Journal of Ergonomics

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Personal computers (PCs) that employ a graphical user interface (GUI) widely exist in our daily lives. Therefore, we have regular opportunities to use operating systems (OS) and application software by means of a pointing device such as a mouse. When a GUI-based OS is used, the pointing operation time (MT) can be minimized by adjusting the display/control (D/C) ratio, which refers to the operation sensitivity of the mouse. The main pointing operation involves positioning the pointer on the desired icon and clicking it. This operation can be classified in terms of movement and positioning. In previous studies, the relation between the D/C ratio and movement time (MTm) was found to be linear, whereas the relation between the D/C ratio and positioning time (MTp) was found to be second-order curvilinear. In this study, the MTp/MT ratio was used as an evaluation index and the relation between the D/C ratio and MTp/MT ratios was discussed. A pointing operation task was designed and conducted with eight able-bodied persons and five cerebral-palsy patients. In both subject groups, the MTp/MT ratio was minimized within the range of the given D/C ratio condition. However, the MTp/MT ratio at the optimum D/C ratio showed higher. To improve the efficiency of the pointing operation of cerebral palsy patients, methods related to improving devices or expanding icon size were employed. This study confirmed that pointing operation efficiency in cerebral palsy patients can be improved by adjusting the D/C ratio. Furthermore, this method is effective in terms of being barrier-free design.

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The sense of busyness often reported by workers who are requested to keep high level of safety. Therefore, it is important to clarify a meaning of the sense of busyness. The present paper describes an experimental study on the relationship between “the sense of busyness” and MWL (Mental Workload) resulting from some simple desk work as a task. In Experiment, the relationship between the sense of busyness and MWL was investigated under 4 busyness conditions suggested by previous studies. As a result, a high positive correlation between sense of busyness and MWL was found, suggesting that sense of busyness may be affected by some other sub-factors included in MWL different from time pressure. For instance, it was found that feeling of “frustration” may be one of them. The finding of this study may contribute to the understanding and reduction of human errors.

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Proposed here is a clustering method of individual differences on working posture so as to improve prediction accuracy of working posture generation. The proposed method was applied to object holding posture in the sagittal plane, and its validity was examined. Twelve subjects were required to hold an object in different holding points and object masses, and five joint angles (i.e. the trunk flexion, shoulder, elbow, knee, and ankle joint angles) were measured. The proposed method was applied to the measurement result and it quantitatively revealed that the knee and ankle joint angles were sources of individual differences. The subjects were divided into three clusters: the first cluster with light body mass, the second cluster with middle body mass, and the third cluster with heavy body mass. The individual differences of holding posture especially appeared in the low holding point. The first cluster extended their knee joint whereas the second and third clusters flexed theirs. The prediction accuracy of knee and ankle joint angle was significantly improved with dividing the subjects into clusters that have similar working posture.

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