Incremental adaptation to yaw head movements during 30 RPM centrifugation

Abstract

Artificial Gravity (AG) provided by short-radius centrifugation is a promising countermeasure against the harmful physiological effects of prolonged weightlessness. However, the vestibular stimulus associated with making head movements while rotating presents a challenge. During a head movement, the semicircular canals are excited by a cross-coupled angular acceleration, resulting in tumbling sensations, perceived body tilt, non-compensatory vertical nystagmus, and motion sickness. Past experiments in the Man Vehicle Lab have studied adaptation to yaw head movements while rotating at 23 RPM. To investigate adaptation to head movements at a higher rotation rate, 28 subjects participated in a 3-Day protocol in which centrifuge velocity was incremented from 14 RPM on Day 1, to 23 RPM on Day 2, to 30 RPM on Day 3. Key findings included: 1) 24 subjects completed the protocol with average motion sickness levels remaining below 5 (out of 20). Feasibility of head movements at 30 RPM was demonstrated, suggesting that adaptation to higher rotation rates may be possible.

(cont.) 2) A motion sickness model used in conjunction with a quantitative semi-circular canal sensory conflict model and an adaptation parameter was effective in making general predictions of motion sickness and adaptation over the 3 days. 3) Intensity and duration of tumbling sensations adapted significantly over the 3 days. 4) The VOR time constant decreased significantly over the 3 days and appeared to reach a limit of approximately 3.5 seconds, which is near the estimated cupular time constant.