The postural control moment in sagittal plane calculated from the center of foot pressure (COP) was evaluated when the impulsive disturbance was applied by the trank traction. The transfer function, with second order denominator and one order numerator, from the disturbance to the postural control moment was identified using the output error minimum (OEM) method. The DC gain increased from -0.4 to 6.6dB and the natural freqency of the denominator decreased from 1.0 to 0.7Hz with the increase of the disturbance torque ranged from 91Nm to 156Nm. These changes imply nonlinear properties of the postural control system. However, no significant differences were observed in DC gain and the natural frequency while the disturbance torque ranged from 156 to 216Nm. When the forward and backward 156Nm disturbances were applied, the maximal position of COP were MP joint and ankle joint respectively. Therefore, the nonlinear properties are attributed to the foot joint mechanism. Implications of findings are also discussed about nonlinear properties of the foot joint mechanism and the postural controller.

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The viscoelastic elements of muscle play an important role in control and stability of human movement. The viscoelasticity is not constant but changes its magnitude depending on the muscle tension, length and contracting velocity. The aim of the present investigation was to develop a torque actuator with viscoelasticity simulating the mechanical property of human muscle. The viscoelastic torque was produced by adjusting the magnitude of torque generated by an induction motor through an electromagnetic powder clutch. The powder clutch possesses intrinsically hysteresis, nonlinearity and a limit to quick response. After examining a current drive, which provided large hysteresis and higher response, and a voltage drive, which had reciprocal characteristics to the current drive, a pulse width modulation with their intermediate characteristics was used for driving the powder clutch. Furthermore, torque feedback and push-pull operation of two powder clutches with different direction led to greater correction in hysteresis, linearity and response. Viscoelastic torque to 150kg·cm was produced stably by feeding angle and angular velocity back. Electromyographic activities of biceps brachii muscle in elbow joint flexion with external viscoelastic load generated by this equipment were discussed.

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The authors have previously reported that the human operator in the two-dimensional tracking system represented an anisotropic phenomenon, i. e., a phenomenon in which the operator exhibited different control characteristics depending upon the direction of the polarity reversal with respect to the controlled object. Furthermore, they hypothesized that the anisotropy was derived from the bilaterality of the brain. In this paper, the adequacy of the hypothesis has been evaluated by analyzing the effect of learning done by the operator and the effect of varying the amplitude of the reference signal on the anisotropic phenomenon. This leads to the discussion of a function found in the central nervous system to integrate information from different sensory modalities. Two kinds of indices obtained from the coherency function of the tracking system were used to evaluate the anisotropy. It has been revealed that the anisotropy appearing in the non-reversed (normal) components of these indices had a strong tendency to decrease as learning progressed while the anisotropy appearing in the reversed components had a weak tendency, and that the anisotropy appearing in the non-reversed components decreased as the amplitude of the reference input to the tracking system was decreased. By the use of a structural model of the information pathway in the brain, it can be explained that the above facts are consistent with the author's hypothesis.

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Concerning the better display for the visual stimuli, one of the key parameters for the matching with the human short-term memory is the presentation time of the information. We have studied on the optimum-apportionment modes of the presentation time of sequentially presented seven capital alphabet characters on five young males by means of our time-continuous model of the short-term memory. These modes are thought to allow the easiest retention in the short-term memory. The average optimum-apportionment mode, as an average of individual scores of the optimum-apportionment mode, was also obtained. With free-recall experiments on the alphabet, four constants of the model were determined on the subjects, respectively. Then, the theoretical optimum-apportionment modes were calculated with the computer simulation on the model of the individual. By slight modifications on these results, eight types of the apportionment mode were obtained. The most efficient mode for the recall of the alphabets in the free-recall experiment was determined as the optimum-apportionment mode of the individual. As the experimental results, the presentation time in the first several characters was long, while the one for the latter part of the sequence was short. These apportionment modes can be applied to the cases with seven symbols, each of which expresses some information of indication, warning, situation, and so on, which is presented sequentially in the same position.

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In this paper, we discuss an ARX (AuoRegressive eXogenous) model concerned with the acceleration and the blood pressure for some healthy volunteers at the emergency brake of an ambulance. Recently, a problem that patients die in the ambulance, that is called DOA (Dead On Arrival), is getting attention. The reason for DOA is not only the development of patient's disease or lack of prehospital treatment but also the vibration of the ambulance. We have already had a result that the blood pressure of a finger changes when the ambulance accelerates or decelrates. As the blood pressure variation may cause serious damage for a patient who has circulatory disease, it is necessary to put a system which absorbs the vibration to reduce the blood pressure variation on the ambulance. To design the system, we propose an ARX model which can be formed using only the experimental data of the acceleration and the blood pressure variation without mechanical characteristics of a human body. We use a tilting bed to measure the relation between the blood pressure and the acceleration of gravity acting from head to leg of a human body, and developed the models of several order. As a result, we have confirmed that a 3rd order ARX model can quantitatively explain the transitional variation of the blood pressure at the deceleration of the ambulance.

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When two stimuli are given sequentially with optimal stimulus onset asynchrony (SOA) and spatial separation (SS), a continuous stimulus moving sensation, called an “apparent movement, ” can be perceived. Two processes, short-range process and long-range process, have been proposed in visual apparent movement. In this paper psychological measurements of long-range apparent movement in central and peripheral vision were performed to compare the optimal SOA and SS. Optimal ranges of SOA were between 80ms and 160ms in both central and peripheral vision, optimal SS in central vision were less than 2° in visual angle, while in peripheral vision SS were greater than 6°. The optimal conditions in short-range process were also measured by using random dot patterns, and were compared with the results of long-range process. Moreover, spatio-temporal properties of evoked potential topography associated with the perception of long-range apparent movement were investigated.

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Fourteen patients (17 cases) were treated with the whole brain irradiation. Physiological changes in white matter were measured by in vivo ¹H magnetic resonance spectroscopy (¹H-MRS). Phantom examination proved the accuracy of our ¹H-MRS method to be valid. The measurement was performed 2 or 3 times in each case at the radiation doses ranged from 0 to 40Gy with 2Gy daily fractionation. For the measurement of ¹H-MRS, 1.5T whole body MR system was used and stimulated echo aquisition mode (STEAM) with chemical shift selective (CHESS) pulse was applied. Volume of the interest (VOI) was 2.5×2.5×2.5cm³, and the repetiton time and echo time were, 2, 000ms and 272ms, respectively. The acute radiation damage of brain was evaluated by the change of peak area ratio (PAR) of choline, creatine and N-acetyl aspartate (NAA). ¹H-MRS spectra before irradiation were different from those observed during irradiation. There were statistically significant (p<0.01) in the choline/creatine ratio between the irradiated group and preirradiated group. Noteworthy, the change of choline/creatine ratio showed good correlation with irradiated dose (correlation coefficient=0.91). As PAR seems to correlate with irradiated dose, it is suggested that choline/creatine ratio might be a useful indicator which reflects the acute radiation damage of brain. ¹H-MRS is a powerful modality, detecting the subtle physiological change which is difficult to evaluate with conventional images.

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