The investigation of the perception of the position where the somatosensory information changes sharply with forward and backward leaning.

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It is conceivable that standing position in the antero-posterior direction is perceived based on the change of the somatosensory information with forward and backward leaning. To clarify the following three problems, this research was executed for 11 subjects. 1) Is it possible to perceive accurately a sharp change in foot pressure and muscle activity with the body leaning? 2) How does the perception of a sharp change in foot pressure and muscle activity vary when a specific part of foot sole is cooled to make the pressure sensation less sensitive? 3) How does the perception of pressure intensity in a specific part of foot sole vary when information of pressure sensation is reduced by cooling the first toe or the first metatarsal head? Results and discussion : All of the subjects were able to perceive the maximal value of the first metatarsal head pressure, but they were not able to perceive the early sharp increase of the first toe pressure, they mis-perceived the latter sharp increas … More e for the early one. In the perception of the activities of abductor hallucis, rectus femoris, and tibialis anterior, eight out of 11 subjects mis-perceived the latter sharp increase for the early one. The suggestions were obtained as follows. The latter sharp increase of the first toe pressure and abductor hallucis activity related to the pressure shifting from the first metatarsal head to the first toe after the first metatarsal head reaching the maximal value. The pressure sensation from the first metatarsal head pressure strongly took part in the perception of the latter sharp increase of the first toe pressure. The pressure sensation from the first toe took part in the latter sharp increase of abductor hallucis. There were individual variations of the relationship with pressure information from the heel in the perception of rectus femoris activity. On the other hand, there was a few in tibialis anterior. To perceive intensity of the first toe pressure, the pressure information from the first toe became important in a position where the first toe pressure rose, and the pressure information from the first metatarsal head became important in a position where the pressure shifted from the first metatarsal head to the first toe. To perceive intensity of the first metatarsal head pressure, the pressure information from the first metatarsal head ranging from low pressure to high was important. Less