A new method of reliability analysis for plant human activities developed by us has been already reported in this journal. We intend here a relatively complex casestudy, applying our method as our further investigation. Because of the fact that our method is still under examination, we choose an example problem having a result from other analytical method, i.e., event tree analysis, to be analyzed by our method. This choice yields the convenience of the comparison of our result with the other.
From this investigation we obtain a result that our method has some advantage with respect to the analysis task and the model description, when the reliability structure of human activities has complexity, comparing the usual event tree analysis.
On the other hand, we evaluated the relation between the redundant structure of human activities and the stability of the total task reliability, using a sensitivity analysis on the example problem.

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This study was conducted to clarify the physiological response characteristics of the elderly by measuring auditory evoked response with indexes of central nerves (E. E. G.) and peripheral nerves (S. P. A. and H. R.) to find response differences on each index.
Comparison was made between the responses of two age groups, an elderly group of 9 males (average age of 71) and a younger group of 13 males (average age of 27). The E. E. G. curve, which is the average of 30 responses to testings of a sound stimulus, indicates no difference between the two age groups. However, with S. P. A. and H. R., the elderly group showed less response than the younger group. The results indicate that the elderly group tends to become habituated to a given sound stimulus in a shorter period of time than the younger group does.
One of the suggestions drawn from the above findings is that the decrease in the number of nerve fibers which takes place with aging may significantly influence responses through peripheral nerves as shown by the indexes used.

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A learning experiment was performed in order to examine the learning characteristics of the human operator in controlling the second-order lag systems differing in natural frequency and damping factor. From tracking data on learning and transfer trials, error scores and human operator's describing functions were computed. The latter were approximated by the models which were composed of gain constant, time delay and lead- or lag-time constant. These data show that the learning characteristics for natural frequency differ from that for damping factor. It is suggested that the human operator develops his strategy for natural frequency during the learning trials, and that the strategy has a transfer effect. The differences between the learning characteristics of the strategy for low natural frequency and that for high natural frequency were discussed.

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