The purpose of this study is to measure and evaluate the dynamic characteristic of standing balance from the point of view of voluntary control of posture. The experiment, in which a subject shifts the center of gravity of his body right or left according to a step input signal, has been carried about normals and hemiplegic patients. Comparing the experimental data with the seven evaluating parameters determined to quantify the step response, the following results are obtained.
1) There is no difference between the step response to right and left side in normal subjects.
2) The response of normal seems to become worse with advancing in age.
3) The response of hemiplegic patient is worse than the one of normal in speed, repetition and holding of motion.
4) This tendency is more notable as the degree of hemiplegia becomes serious. There are good correlations between evaluation in clinics (Br. stage) and the experimental result.
5) In hemiplegia, it seems that the response to affected side is worse than the one to non-affected side.
The intuitive and quantitative descriptions of the response are proposed in the form of hepta-gram and score so as to make it easy to evaluate patient's impediment objectively in clinics.

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Rapid forearm movements were analysed in order to obtain basic response patterns and to estimate the central control policy. The movement employed is a rapid forearm flexion from horizontal position to a displayed target within the vertical plane. The movement time course can be divided into four phases according to the central control modes. Phases 1 and 2 represent a rapid, distance-covering ballistic movement, Phase 3 is a closed-loop-controlled course approaching the centrally established target and in Phase 4 the forearm is held at the target position. In the first two phases, the change of acceleration is highly stereotyped and can be classified into one of the six basic patterns according to the wave form and the values of motor parameters. Under a certain condition some of the motor parameters including the first peak times of acceleration and velocity are found to be closely related with the onset time of extensor activity. The role of the central motor command and muscle dynamics are briefly discussed in the acceleration pattern formation. Precise visual regulation of the arm position to the given target can occur only in Phase 4.

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In many conventional man-machine studies, the human control responses are analyzed in terms of the linear component and remnant. In this paper remnant is analyzed into two components: the system and the noise components. The noise component is assumed to be due to the psychophysical noise of the operator, while the system component is responsible to the way of closed-loop interactions between man and machine.
In the experiments, the existence of the system component is shown by a comparison of the control responses under open and closed loop situations.
Next, it is shown that amplitude and period of the system component exhibit certain variations according to the difference in the plant dynamics. This confirms that mutual interactions between man and machine are essential in formation of the system component. The last experiment shows that the system component increases after sudden change in the input amplitude, period and waveform.
This increase indicates a useful role of the system component in maintaining control accuracy, when sufficient input model is not available due to the sudden change in input.

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