Model of Human-Vehicle Closed Loop Control: Effects of Altered Gravity and Vestibular Sensory Precision

Abstract

The vestibular system provides the brain with information about head motion and orientation relative to gravity, which are important sensory cues for postural control and movement coordination. Due to noise in the nervous system, perceptions of motion and orientation are imprecise. However, the brain can control motion with excellent precision. Thus, we studied the role of noise on behavior in vestibular-normal individuals by utilizing a computation model of a vestibular manual control task. Additionally, to study the effects of gravity on manual control performance, we modeled the task under conditions of (1) Earth gravity, (2) hypo-gravity, and (3) hyper-gravity. Using roll-tilt thresholds and manual control task performance from ten normal subjects, a closed loop model was designed. Simulations were conducted to understand the relationship between vestibular roll-tilt thresholds and performance, as well as the relationship between gravity and performance. The simulations showed manual control performance worsened with decreasing gravity and worsened with increasing vestibular thresholds. We explain the worsening of subject’s performance as a function of vestibular threshold as greater noise alters the brain’s perception of spatial orientation. Given that altered gravity exerts different magnitudes of shearing on the vestibular hair cells, we hypothesize a worsening of subject’s performance in lower gravity due to conflicts with the brain’s internal model of gravity. This modeling is important to understand the effects of gravity on spatial orientation and locomotion during altered gravity events such as space exploration, and to better understand the effects of vestibular noise on behavior.