COMPASS: Computations for Orientation and Motion Perception in Altered Sensorimotor States.

Reliable perception of self-motion and orientation requires the central nervous system (CNS) to adapt to changing environments, stimuli, and sensory organ function. The proposed computations required of neural systems for this adaptation process remain conceptual, limiting our understanding and ability to quantitatively predict adaptation and mitigate any resulting impairment prior to completing adaptation. Here, we have implemented a computational model of the internal calculations involved in the orientation perception system's adaptation to changes in the magnitude of gravity. In summary, we propose that the CNS considers parallel, alternative hypotheses of the parameter of interest (in this case, the CNS's internal estimate of the magnitude of gravity) and uses the associated sensory conflict signals (i.e., difference between sensory measurements and the expectation of them) to sequentially update the posterior probability of each hypothesis using Bayes rule. Over time, an updated central estimate of the internal magnitude of gravity emerges from the posterior probability distribution, which is then used to process sensory information and produce perceptions of self-motion and orientation. We have implemented these hypotheses in a computational model and performed various simulations to demonstrate quantitative model predictions of adaptation of the orientation perception system to changes in the magnitude of gravity, similar to those experienced by astronauts during space exploration missions. These model predictions serve as quantitative hypotheses to inspire future experimental assessments.

Sensorimotor impairment from a new analog of spaceflight-altered neurovestibular cues.

Exposure to microgravity during spaceflight causes central reinterpretations of orientation sensory cues in astronauts, leading to sensorimotor impairment upon return to Earth. Currently there is no ground-based analog for the neurovestibular system relevant to spaceflight. We propose such an analog, which we term the "wheelchair head-immobilization paradigm" (WHIP). Subjects lie on their side on a bed fixed to a modified electric wheelchair, with their head restrained by a custom facemask. WHIP prevents any head tilt relative to gravity, which normally produces coupled stimulation to the otoliths and semicircular canals, but does not occur in microgravity. Decoupled stimulation is produced through translation and rotation on the wheelchair by the subject using a joystick. Following 12 h of WHIP exposure, subjects systematically felt illusory sensations of self-motion when making head tilts and had significant decrements in balance and locomotion function using tasks similar to those assessed in astronauts postspaceflight. These effects were not observed in our control groups without head restraint, suggesting the altered neurovestibular stimulation patterns experienced in WHIP lead to relevant central reinterpretations. We conclude by discussing the findings in light of postspaceflight sensorimotor impairment, WHIP's uses beyond a spaceflight analog, limitations, and future work.NEW & NOTEWORTHY We propose, implement, and demonstrate the feasibility of a new analog for spaceflight-altered neurovestibular stimulation. Following extended exposure to the analog, we found subjects reported illusory self-motion perception. Furthermore, they demonstrated decrements in balance and locomotion, using tasks similar to those used to assess astronaut sensorimotor performance postspaceflight.

A standardized, incremental protocol to increase human tolerance to the cross-coupled illusion.

BACKGROUND: Humans can adapt to the "Coriolis" cross-coupled illusion with repeated exposure, improving the tolerability of faster spin rates and enabling short-radius, intermittent centrifugation for artificial gravity implementation. OBJECTIVE: This investigation assesses the criticality of personalization in acclimation to the cross-coupled illusion. METHODS: We used the median stimulus sequence of our previous effective and tolerable personalized, threshold-based protocol to develop a standardized (non-personalized) approach. During each of 10, 25-minute sessions, the spin rate was incremented independent of whether each subject reported experiencing the cross-coupled illusion. RESULTS: In comparison to the previous personalized protocol, the standardized protocol resulted in significantly reduced acclimation to the cross-coupled illusion (17.7 RPM threshold for the personalized protocol versus 11.8 RPM threshold for the standardized) and generally increased motion sickness reports (average reporting of 1.08/20 (personalized) versus 1.98/20 (standardized)), on average. However, the lack of individualization also leads to significantly less variance in subjects' acclimation. CONCLUSIONS: These findings are critical for future missions that may require several astronauts to be acclimated concurrently, due to resource and time constraints. Assessing feasibility of fast spin rate, short-radius centrifugation is crucial for the future of artificial gravity implementation during spaceflight.

Integration of a Vestibular Model for the Disorientation Research Device Motion Algorithm Application.

INTRODUCTION: Spatial disorientation (SD) remains a leading cause of Class A mishaps and fatalities in aviation. Motion-based flight simulators and other research devices provide the capacity to rigorously study SD in order to develop effective countermeasures. By applying mathematical models of human orientation perception, we propose an approach to improve control algorithms for motion-based flight simulators to study SD.METHODS: The Disorientation Research Device (DRD), or the Kraken™, is the Department of Defense's newest and most capable aerospace medicine motion-based research device. We implemented an "Observer" model for predicting aircrew spatial orientation perception within the DRD, and perceptions experienced in flight. Further, we propose a framework that uses the model output, in addition to pilot control inputs, to optimize multiaxis motion control including human-in-the-loop control capability.RESULTS: A case study was performed to demonstrate the functionality of the framework. Additionally, the case study highlights both how limitations of human perception are crucial to consider when designing motion algorithms, and the challenges of effective flight simulation with multiple motion axes.DISCUSSION: We implemented a mathematical model for spatial orientation perception to improve the design of control algorithms for motion-based flight simulators, using the DRD as an example application. We provide an example of predicting perceptions, producing quantitative information on the efficacy of motion control algorithms. This mathematical model based approach to validating motion control algorithms aims to improve the fidelity of ground-based SD research.Dixon JB, Etgan CA, Horning DS, Clark TK, Folga RV. Integration of a vestibular model for the Disorientation Research Device motion algorithm application. Aerosp Med Hum Perform. 2019; 90(10):901-907.

Tolerable acclimation to the cross-coupled illusion through a 10-day, incremental, personalized protocol.

BACKGROUNDArtificial gravity (AG) has the potential to provide a comprehensive countermeasure mitigating deleterious effects of microgravity. However, the cross-coupled "Coriolis" illusion has prevented using a more feasible and less costly short-radius centrifuge, as compared to large, slowly spinning systems.OBJECTIVEWe assessed tolerability of a personalized, incremental protocol to acclimate humans to the cross-coupled illusion, enabling faster spin rates.METHODSTen subjects were exposed to the illusion by performing roll head tilts while seated upright and spun about an Earth-vertical axis. The spin rate was incremented when head tilts did not subjectively elicit the illusion. Subjects completed one 25-minute session on each of 10 days.RESULTSThe spin rate at which subjects felt no cross-coupled illusion increased in all subjects from an average of 1.8 rotations per minute (RPM) (SD: ±0.9) at the beginning of the protocol to 17.7 RPM (SD: ±9.1) at the end. For off-axis centrifugation producing 1G at the rider's feet, this corresponds to a reduction in the required centrifuge diameter from 552.2 to 5.7 meters. Subjects reported no more than slight motion sickness.CONCLUSIONSAcclimation to the cross-coupled illusion, such as that accomplished here, is critical for feasibility of short-radius centrifugation for AG implementation.