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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.

Background: Stochastic resonance (SR) refers to a faint signal being enhanced with the addition of white noise. Previous studies have found that vestibular perceptual thresholds are lowered with noisy galvanic vestibular stimulation (i.e., "in-channel" SR). Auditory white noise has been shown to improve tactile and visual thresholds, suggesting "cross-modal" SR. Objective: We aimed to study the cross-modal impact of noisy galvanic vestibular stimulation (nGVS) (n=9 subjects) on visual and auditory thresholds. Methods: We measured auditory and visual perceptual thresholds of human subjects across a swath of different nGVS levels in order to determine if a subject-specific best nGVS level elicited a reduction in thresholds as compared the no noise condition (sham). Results: We found an 18% improvement in visual thresholds (p = 0.026). Among the 7 of 9 subjects with reduced thresholds, the average improvement was 26%. Subjects with higher (worse) visual thresholds with no stimulation (sham) improved more than those with lower thresholds (p = 0.005). Auditory thresholds were unchanged by vestibular stimulation. Conclusions: These results are the first demonstration of cross-modal improvement with nGVS, indicating galvanic vestibular white noise can produce cross-modal improvements in some sensory channels, but not all., 15 pages, 7 figures

Astronauts on future deep space exploration missions will need to maintain excellent performance to ensure safety and mission success. To enhance neurocognitive and task performance, stochastic resonance (SR) may be used to enhance “information transfer” to the brain across multiple sensory modalities, reducing the cognitive workload associated with complex tasks. SR is achieved when white noise is added to a perceptual channel (e.g., auditory, vestibular, visual, etc.), and resonates with the underlying primary signal. Our overarching study seeks to examine SR in the context of improved perceptual thresholds; specifically, we hypothesize humans can perceive smaller magnitude stimuli with the addition of SR white noise. In this paper, we introduce a novel approach to experimental design aimed at reducing the time necessary for accurate and precise perceptual threshold measurement. In the two-interval task used for this study, the subject must indicate which of the two intervals they thought the stimulus occurred in (stimulus detection). A stimulus detection task has been chosen to avoid biases in the subject's decision criteria. Each two interval sequence is called a trial; by collecting binary (correct, not correct) data on a given subject (at a given SR noise level) over a series of trials, a threshold can be estimated by fitting a psychometric curve. Measurement of thresholds can be exhausting for subjects, especially if many thresholds are measured in quick succession. Therefore, to avoid fatigue confounding performance it is important that the number of trials, and thus time, are minimized. To this effect, we use computational methods to simulate threshold measurement. The simulations seek to show how many trials are necessary for a threshold measurement accurate and precise enough to discern the presence of SR. With such simulations, we have developed an experimental design that is likely to identify SR if it exists while minimizing the number of trials required.

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.

During space exploration missions, prolonged exposure to microgravity causes physiological deconditioning in astronauts. Artificial gravity (AG) through centrifugation has the potential be a comprehensive countermeasure to this deconditioning. However, a fast spinning environment causes the Coriolis cross-coupled (CC) illusion when head tilts are made, which is disorienting and leads to motion sickness. To reduce the spin rate, a much larger centrifuge is required to produce a desired gravitational level. Previous research has shown humans can be adapted to the CC illusion, such that higher spin rates become tolerable with training. However, it remains unclear if this adaptation can be retained for an extended period of time (e.g., If the training occurs pre-flight, how much is retained by the time astronauts are centrifuged in transit?). In the current study, we investigated CC illusion training retention by retesting subjects after 30 days since the conclusion of their original 10-day training. We compared the level of adaptation (i.e., the spin rate at which the CC illusion was just barely sub-threshold) in three days of retention tests to their level at the end of the original 10-day training and to the first three days of original training in a control group (never experienced any prior training). Preliminary results suggest that a substantial portion of the original adaptation was retained, even after this extended layoff. The CC illusion threshold was lower in some subjects after 30 days off compared to that individual's threshold at the end of the 10-day training period; however, it was typically higher than pretraining thresholds, suggesting some level of retention. Furthermore, across three consecutive days of retraining, some subjects tended to increase their CC illusion threshold much more quickly than during the first three days of the original training. This retained training may make AG a more feasible countermeasure for spaceflight-induced physiological deconditioning, enhancing human space exploration capabilities.