This paper describes new observations on characteristics of a human operator in manual control systems and a new design method of compensators considering operator maneuverability using these observations.
At first, we performed experiments on a pursuit manual control system with the control object realized on a computer. By analyzing the experimental results, two new properties of a human operator are explored which are useful for design of manual control systems. One is on loop-shaping characteristics of a human operator which is an extension of the ordinary crossover model. The other is on relations between pursuit performance and maneuverability. Secondly, we introduce a new design method of manual control systems aiming at maneuverability, combining the explored properties with abilities of H_∞ control theory in shaping frequency transfer characteristics of control systems. Finally, validity of the design method is confirmed by experiments.

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Based on a video taped study of human hand movements during practical tactile evaluation of the human skin, evaluation patterns of softness, elasticity, pliability, smoothness were observed. These movements were classified into two handling patterns, pressing and sliding. In order to measure strokes of a forefinger, a luminous element diode was attached to the forefinger and its movement was measured by an infrared position-sensing system.
Next experiment was designed to determine the scaling values of softness and elasticity obtained by a round robin pair testing by the Scheffe's method. Sensory evaluations were conducted on the dynamic properties of several rubber samples with properties closely resembling the softness and elasticity of the human skin.
The evaluation models were extracted from these analyses and applied to the development of detecting method for the dynamic properties of the human skin. These experiments suggest the probability of application of a study on the tactile perception in the cosmetic field through an ergonomic approach to human skills.

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This study was made to propose a model which was able to describe the relationship among the quantity of the presented character-information, the difficulty of the information transition and the error-ratio as a guide of the upper limitation of the presented character-information. The model was the statistical model derived from the short-term memory decay and the interference in the working memory by referring the psychological findings. The relationship between the quantity of the presented character-information and the error-ratio in four levels of the task which differs the difficulty of the information transition, was examined for the evaluation of the model, and the degree of the fitness was evaluated by goodness of fit test (the two-sided chi-square test). It was found that the fitness of the model made for this experiment was good enough in the small difference of the difficulty of the information transition. Additionally the degree of the fitness of the model was evaluated by the results of three other information transition task using different kinds of the character. Based upon the evaluation, the fitness of the model was also good regardless of the big difference of the difficulty of the information transition and the kinds of the character. These results revealed that the fitting range of the model was wide for the information transition tasks.
It is concluded that the proposed model can be widely applied for the description of the relationship among the quantity of the presented character-information, the difficulty of the information transition and the error-ratio in many kinds of the information transition tasks.

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The present paper deals with error occurrence in information processing of the characters presented on the VDT for the purpose of designing human interface in which one can response more accurate than in the conventional designs by carrying out two experiments on information processing work using alphabetical characters. The purpose of Experiment 1 is to test the time series variation of error occurrence in the work of information processing by using 15 subjects. 1/f fluctuation of error occurrence of information processing work was observed in all the subjects used. In order to explain this manner of error occurrence, a new conceptual hypothesis proposed that working memory capacity varies was prepared for Experiment 2. The time series variation of information processing time on working memory was testified by applying simple reaction task and selective reaction task requested to the different group of 15 subjects from the ones used in Experiment 1. The variation of white noise in information processing time on working memory was observed in Experiment 2. Confirmation of new conceptual hypothesis was made by this result. It was suggested that error occurrence of information processing work was caused by the variation of working memory capacity and that 1/f fluctuation in the intervals of error occurrence was caused by the variation of white noise of working memory capacity.

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The acoustic myogram (AMG) is considered to originate from a pressure wave generating in the contracting muscle fibers. The present study was intended to determine the activation pattern of muscle fibers during fatiguing sustained contraction by the acoustic myography. Subjects were asked to maintain isometric contractions of biceps brachii muscles for force equivalent to 20% and 60% maximum voluntary contraction (MVC) until exhaustion. At 20% MVC task, the AMG power increased monotonically up to exhaustion and the increments became remarkable from 50% of endurance time (% Time). The power spectrum changed significantly between the onset and 50% Time from unimodal to multimodal distribution. The fatiguing task at 60% MVC demonstrated a nonunivocal trend in the power, namely, progressive increase in the power until 50% Time was followed by the decrease thereafter. The multimodality in the power spectrum was preserved throughout the task, and was accompanied with significant increase in higher frequency contents after 50% Time. The AMG appears to reflect the activation pattern of muscle fibers characterized not only by the number, types and location of muscle fibers but also by their firing rate. In addition, this signal is considered to be useful to assess muscle fatigue.

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An attempt was made to evaluate the subjective fatigue level in motorcycle (MC) riding and that in automobile (AM) driving in accordance with the Fatigue Scale (FS) proposed by The Industrial Fatigue Research Committee of the Japan Association of Industrial Health. Field tests with the mileage over 400km were conducted for 30 subjects riding a MC and for 20 subjects driving an AM. In each test, the subject was asked to fill the FS questionnaire with 30 items adapting the five-point rating method at the start point, 5 points on the route and the finish point. As a result of factor analysis, three common components, “drowsiness and dullness”, “difficulty in concentration” and “projection of physical disintegration” were extracted from the data of both subjects groups. “Drowsiness and dullness” in MC riding are supposed to reflect the combination of physical and mental strain while those in AM driving mainly reflect mental strain, and it is believed that the FS is applicable to a quantitative evaluation of the subjective fatigue level in MC riding to a certain degree. On the contrary, it turned out that the applicability of the FS to that in AM driving was quite limited and there is a need for developing a new evaluation method to promote driving safety.

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The effects of the surface and texture of various foods on human preference are examined using rating scale test. The food tested are raw carrot, steamed fish paste and bean curd. The foods are formed into the following surfaces: smooth type, cross stripes cutting type, hole type, wave type and sharp type. The results are as follows.
1. The only smooth type is significantly preferred in very soft food (bean curd).
2. The expressions for five kinds of the food surfaces are different.
3. There is no a difference in preference between the subjects who needed less chewing cycles until last swallowing action and those who needed more chewing cycles.
These results suggest that the preference of food surfaces is different in food texture.

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