Contribution of lower limb somatosensation to perception of linear acceleration in standing posture

Abstract

The central nervous system perceives body motion usingmulti-sensory cues such as vision, vestibular information, and somatosensation. Among these sensory cues, previous research reported that pressure sense from soles and proprioception of legs, that is, lower limb somatosensation are strongly correlated with the perception of motion in standing posture. Methods: To determine whether lower limb somatosensory cues contribute to perception of motion in standing posture and which sensation of lower limb plays dominant role, we examined the changes in detection threshold of the movement direction with and without lower limb somatosensory constraints.As lower limb somatosensory constraints, we used ankle brace for proprioception of ankle and compliant support surface for pressure from sole. Subjects experienced four conditions of experiment: no restraint, restrained ankle, reduced tactile sense from sole, and constrained both of them. In each conditions, six healthy male volunteers (aged 21~ 26 years) stood on a servocontrolled translational platform in the dark with barefoot. The series of randomly sequenced single sinusoidal acceleration at 0.25Hz were used as stimulus. The platform was translated to either subject’s left or right with peak acceleration magnitude ranged from 0 to 8mG. After each stimulus, subjects reported their perceived direction of motion by pressing hand held buttons. We defined the magnitude of perception threshold as the stimulus at the performance level of 75% using psychometric function. Results:Wefound that reduced lower limb somatosensation significantly increased the perception threshold of linear motion.Without constraints, mean threshold was 0.82±0.23mG, while it was 1.23±0.35mG with reduced lower limb somatosensation.Moreover, when restrained pressure cues of sole, the threshold more increased than the reduced ankle proprioception condition. Conclusions:These results indicate thatwithout visual cues, lower limb somatosensory information affect perception of motion and the pressure sense from sole takes charge of a superior part in these cues. These results suggest that appropriate complement to a solemay be useful for improving the linear motion detection.