Our previous works revealed that the equilibrium perception detected by the subjective upright posture is affected from the motor-learning of the balancing task even in the seated posture. However, the same motor learning sometimes evoked the different perceptual change, the shift of the subjective upright posture in the opposite direction. Investigating this reason, this paper analyzes the motor-learning that contains two kinds of disturbance: inertial disturbance caused by the lateral slides

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... f the whole stool, and rotating disturbance featured by the shift of the virtual rotation axis of the stool roll direction. As the results, three factors, the relative phase of CoP with respect to the motion of the virtual rotation axis and the sign and the magnitude of the mean horizontal deviation of the trunk, specify two kinds of posture during the motor learning. At one posture, the trunk inclines at the basis near the pelvis to the same direction of the disturbance and shows a large horizontal deviation measured at the neck. On the other hand, at the other posture, the trunk bends first to the same direction of the disturbance at the base and bends again to the opposite direction near the waist, indicating a small horizontal deviation. The posture of the balancing task during the motor learning seems to determine the direction of the perceptual change for the participants that have reduced the relative phase, i.e., the delay, of CoP movement from the disturbance implying the progression of the motor learning.