Novel neurodigital interface reduces motion sickness in virtual reality

Virtual reality (VR) is a computer-created 3D environment with a focus on realistic scenes and pictures created for entertainment, medical and/or educational and training purposes. One of the major side effects of VR immersion reported in the scientific literature, media and social media is Visually Induced Motion Sickness (VIMS), with clinical symptoms such as disorientation, nausea, and oculomotor discomfort. VIMS is mostly caused by the discrepancy between the visual and vestibular systems and can lead to dizziness, nausea, and disorientation. In this study, we present one potential novel solution to combat motion sickness in VR, showcasing a significant reduction of nausea in VR users employing the META Quest 2 headsets in conjunction with a whole-body controller. Using a neurodigital approach, we facilitate a more immersive and comfortable VR experience. Our findings indicate a marked reduction in VR-induced nausea, paving the way to promote VR technology for broader applications across various fields.


Introduction
Virtual reality (VR) is a computer-created 3D environment with a focus on realistic scenes and pictures created for entertainment, medical and/or educational and training purposes.The scenes and pictures are presented through VR headsets, or rarely, through helmets, and most content requires some type of locomotion to achieve the most realistic feeling.The major benefits are that it allows the creation of a virtual world around the user and therefore enhances many activities.
However, VR's expansion is hindered by VR-induced motion sickness, also termed as Virtual Reality Sickness, Visually Induced Motion Sickness (VIMS), or cybersickness.VIMS has attracted considerable attention due to its impact on user experience and potential implications for immersive technology adoption.VIMS encompasses symptoms such as nausea, dizziness, headaches, sweating, eye strain, and subjective discomfort occurring during or after VR exposure [1].Existing studies estimate that 30 %− 80 % of the population experience VR-induced motion sickness following virtual reality use [2].The genesis of VRinduced motion sickness is thought to arise from sensory conflicts experienced by VR use, where there is a discord between visual cues perceived in VR and the signals originating from the user's vestibular and proprioceptive systems, producing subsequent disorientation.Detection of cybersickness often relies on questionnaires assessing symptoms, postural instability tests, and monitoring vital signs such as heart rate, blood pressure, respiration, electrocardiogram, and electrogastrogram readings [3].Factors influencing VR-induced motion sickness include the visual movements, user locomotion, exposure duration, age [4], gender [5], prior VR experience, and physiological attributes including vestibular function [6,7].Effective strategies for mitigating VR-induced motion sickness closely parallel techniques used to reduce general motion sickness, which primarily means discontinuing the uncomfortable stimuli [8].Additional approaches include shorter VR sessions, maximizing visibility of VR surroundings, moderating ambient temperature, and employing anti-nausea medications [9].Despite posing challenges, paradoxically, VR technology itself exhibits potential as an emerging preventative and therapeutic option for motion sickness [10].
The present study aimed to explore the ability of a new neurodigital interface, C-Infinity, with the natural orthostatic position, minimal space utilization, and capability for body movement, allowing better alignment of visual and proprioceptive inputs, to reduce nausea in users susceptible to VIMS in VR.Our team investigated C-Infinity, a neurodigital interface designed to better align multisensory inputs by employing whole-body control in VR by using the standing position and proprioceptive feedback to reduce VIMS.C-Infinity was designed to use motion sensors and haptic feedback to enable the users to control their virtual movements with their whole body rather than solely their head and hands.We hypothesized that the standing position, which is a natural orthostatic position, coupled with small movements generated by the upper body for the lateral moves and turns in the VR, as well as the slight pressure generated with fingers and hand palms for forward and backward movement, when combined with visual confirmation of the movement in the VR, alleviates motion sickness.
To test this hypothesis, we recruited 12 healthy volunteers with VR gaming experience to test them for their susceptibility to developing VIMS upon 3 min of motion in VR using Quest 2 Headset, one of the commonly used headsets.Rationale for the time selected is based on our interest in reducing rapidly developing VIMS, which usually happens within the first 2-3 min upon experiencing locomotion in VR.It is well established that around 50 % of the general population develops motion sickness in VR after a short usage, so we performed the initial screen to identify susceptible subpopulations.Once susceptible users were identified, we performed a comparative study between standard gamepad controllers and C-Infinity to measure the physiological and health impact on the users.
Preliminary results suggests that C-Infinity significantly mitigates nausea and improves VR experience, making it the first employment of neurodigital interface for VIMS prevention.Our approach could be especially beneficial for users with mobility impairments, such that the sensation of locomotion can be realized through VR in a safe and more pleasant way, expanding VR's applicability for education, training, therapy, and entertainment.

Methods
For this study, we designed the experiments based on inductive reasoning, combining laboratory and field testing [11].

Subjects
Twelve healthy adult males without cardiovascular diseases, diabetes, gastrointestinal, or renal diseases were selected using random sampling to participate in the study.Within those a subgroup of seven subjects were identified as "responders" that developed nausea using the Gamepad with VR.Basic anthropometric characteristics were as follows: age − 32.9 ± 11.5 years; body height, BH − 184.4 ± 8.2 cm; body mass, BM − 81.9 ± 10.5 kg; body mass index, BMI − 24.04 ± 2.24 kg⋅m − 2 .All subjects had recreational experience of playing VR games i.e. they had experience using VR technology (Supplementary Table ).

Ethics declarations
All of the participants were informed about the study procedures and research goals and gave their written consent to participate in the study.The research was conducted in line with the "Declaration of Helsinki for recommendations guiding physicians in biomedical research involving human subjects" (https://www.cirp.org/library/ethics/helsinki/).The study was approved by the Ethical Committee of Faculty of Sports and Physical Education, University of Belgrade (protocol No. 484-2).

Gamepad and c-infinity protocol
For our studies described in this paper, we have used two different input devices as controllers for VR: (i) C-Infinity VR chair from Neuro-Sync Laboratories (Fig. 1A and Fig. 1B), https://neurosyncvr.com/; and (ii) standard wired Xbox 360 Gamepad (Fig. 1C).
Software used for VR content was developed by NeuroSync Laboratories using Unreal Engine 4, an advanced real-time 3D creation tool for photoreal visuals and immersive experiences.Briefly, we recreated visual content to represent the underground garage scene, devoid of interactive elements so that the user could move through the garage and between parked cars, facilitating unrestricted navigation (content for research purposes is available upon request from NeuroSync Laboratories).Screenshots from the software with the VR content are shown in Fig. 2. The content is textured and lit realistically and is designed to be fully explorable in less than 3 min.The player has freedom of movement M. Dopsaj et al. but the level design guides the player through the optimal route.The player has full freedom of locomotion to include movements in all directions and rotation: forward, backward, strafe left, strafe right, rotate left, rotate right.To mitigate the risk of VIMS, which predominantly occurs within the first 2-3 min with VR exposure, each participant's session was constrained to 3 min.The presence in VR for less than 3 min induces VIMS for a period of about 10 min after VR experience, while the presence in VR for more than 3 min can induce VIMS that lasts the whole day.

Physiologic testing procedures
For the purposes of this research, we collected objective data on general muscle isometric strength potential, cardiovascular and metabolic effects (quantitative), as well as nausea after different VR modalities (semi-quantitative).

Hand grip
For the isometric hand grip (HG) testing, a protocol with standardized procedures and equipment (All4gym d.o.o., Serbia) was used [12,13,18].The participants were sitting upright centrally in the chair during the test, with tested arm naturally by their side and slightly abducted from the body (approximately 5 cm).The opposite arm was resting alongside the body passively and the participants were prohibited to move or have any kind of physical support during the testing.Prior to the main assessment, all subjects were given a detailed testing explanation and have initially performed two pre-trial sub-maximal measurements by alternating hands with a rest period of two minutes for each hand.In the main power grip test, the subjects were asked to perform the strongest and fastest possible (explosive force) grip trial by maintaining the grip for 2 s or until a verbal cue to stop was given by the measurer.The HG test of the dominant and non-dominant hand was conducted twice (in a randomized order) with a one-minute interval between different hand trials.
There is strong evidence in the scientific literature that HG serves as a highly dependable measure of estimating individual's physical capabilities, encompassing the genetic, biological and behavioral attributes.It has also been proven that it represents a straightforward marker of general body power and strength in across genders and life stages from childhood to adulthood [19][20][21][22][23].

Blood Lactate concentration
Lactate concentration was measured in capillary blood samples from a finger prick using a portable new-generation lactate analyzer (Lactate Plus NOVA biomedical, USA).The samples were taken as follows: initial lactate concentration level (pre-testing at rest) and final lactate concentration level (3 min after each VR).For collecting the blood sample, a disposable blood lancet Unistik 3 Comfort (Owen Mumford Ltd.UK) was used [14,15], where a sample of 0.7 μl capillary blood from finger was extracted.

Heart rate
Heart rate (HR) was measured using the Polar H10 sensor (https://www.polar.com/en/sensors/h10-heart-rate-sensor).The initial HR value was measured at rest, where the subjects were in a semi-supine position and completely relaxed.The HR value at rest represented the lowest HR value recorded in the period between the second and third minutes of the given rest.The peak HR represented the HR value was recorded immediately after the completed modalities of the VR task as a functional exertion of the cardiovascular system.

Assessment of nausea
Nausea, being inherently subjective, lacks a definitive objective method of measurement, thus cannot be assessed without the participant disclosing to the observer.Therefore, we relied on the participants' self-reports for assessment of nausea, in line with established methodologies [17,24].

Variables
We evaluated several variables to assess isometric strength, neuromechanical characteristics, metabolic responses, and subjective experiences of nausea during VR activity.
HG muscle force as indicators of overall body isometric strength and neuro-mechanical characteristics of the arm (upper body) muscles were gauged using the following metrics [18,25,26 The assessment of nausea was carried out according to previously defined methodology and criteria [17,24,27].To assess the intensity of nausea, a five-part Likert-type numerical rating scale was used (at 0.5 sensitivity), and the duration of nausea was measured by the chronometry method using a hand stopwatch (Epsan, Selecta, Traceable® 60-memory Stopwatch, Texas, USA) from the end of VR exposure until the complete resolution of nausea.The quantity of nausea, as a measure of its load, was calculated as a product of intensity and duration [17,24].Specific nausea variables were: 1. Maximal intensity (NAUS INT ) -defined as the highest value of the score between 1 (no nausea) and 5 (maximal intensive nausea), expressed as the numerical score with 0.5 point increments 2. Duration of nausea (NAUS DUR ) -subjects were asked at 30-second intervals to subjectively evaluate the intensity of nausea they had experienced during the analyzed time period, expressed in seconds (s); 3. Quantity (NAUS QT ) -Calculated as the products of the intensity multiplied by the duration of nausea time (NAUS QT = NAUS INT NAUS DUR ), expressed in index number All subjects underwent two different VR modalities tests-Gamepad and C-Infinity-allocated using the randomized testing principle and by the method of random selection, with a one-week inter-session interval.Detailed analysis focused exclusively on and included only subjects who have experienced nausea.

Statistical analysis
All analyses were realized by IBM SPSS v23.0 statistical software.First, all the raw data underwent descriptive statistical analyses in order for the basic values of central tendency and dispersion (Mean ± SD) to be defined.As a main statistical procedure for differences between groups and tests, we used the MANOVA and ANOVA with the Bonferroni Post Hoc test as a suitable design for our study.The influence of VR modalities on the difference in and between the groups, Partial Eta 2 , was calculated.The difference between VR modalities for each variable is calculated as the average (across samples) relative difference between VR modalities of changes in measured variable after and before testing procedure, and is expressed in % (ΔF max _SUM, ΔRFD max _SUM, ΔtF max _SUM, ΔtRFD max _SUM, ΔLA, ΔHR, ΔNAUS INT ) and as the actual difference between VR modalities of the post testing measurements (ΔNAUS DUR , ΔNAUS QT ).Delta value is calculated per single VR modality according to the formula: ((Test2/Test1) -1)⋅100, where Test1 is the value of the particular variable before (pre) VR modalities testing for a particular subject, and Test2 is the value of the same variable after (post) VR modalities testing for the same subject during (individualized delta value for initial as a pre, and final as a post-testing, expressed in %).All the differences were determined at the probability level of 95 %, based on criterion p ≤ 0.05 [28].

Results
The measured data of all twelve subjects before and after the VR experience using C-Infinity VR chair and Xbox 360 Gamepad, for Hand Grip muscle force, Lactate and cardiovascular metrics, and Nausea variables, with percentage differences are provided in the Supplementary Table.

Hand grip comparison
Evaluation of differences in hand grip between C-Infinity and Gamepad modalities, measured by the differences in muscle isometric strength (HG) before (Initial) and after (Final) VR protocol usage, is presented in Table 1.Despite the p-values showed that there is no statistically significant difference between the VR modalities before and after usage (p-values are between 0.295 for RFDmax_SUM and 0.891 for tFmax_SUM), there is still a discernible trend indicating a greater general effect of the VR modality on the mechanical characteristics of muscle force production (F max _SUM and RFD max _SUM) than on the temporal parameters of their expression (Part.Eta 2 = 8.2 and 9.1 % compared to 0.2 and 0.6 %, respectively).Additionally, when considering the absolute impact of the different effects RFD max _SUM emerges as a more sensitive indicator for defining the effects of differences between the used VR modalities (Table 1, Part.Eta 2 ), where C-Infinity exhibited less impact on maximum force (-5.2 %) while having a greater impact on reducing maximum explosiveness (-15.5 %) compared to the Gamepad.This suggests a greater dynamic activity of the upper body, arms, and hands during the use of C-Infinity compared to the completely static position when using the Gamepad.

Cardiovascular, metabolic, and nausea comparison
Assessment of differences between C-Infinity and Gamepad modalities measured by the comparison of differences of cardiovascular, metabolic, and nausea variables before and after VR protocol, are presented in Table 2.The p-value shows the statistically significant differences in heart rate (HR), maximal intensity (NAUS INT ), duration of nausea (NAUS DUR ), and quantity of nausea (NAUS QT ).Comparison between C-Infinity and Gamepad modalities for these four statistically significant variables are presented as box plots in Fig. 3.

Statistically significant results (p-value < 0.05)
The results showed that the use of VR in the C-Infinity modality had a statistically significant impact on the activation of the cardiovascular system compared to the Gamepad, an increased in HR by 22.6 % compared to 17.8 % (p = 0.047).Additionally, the results showed that the greatest impact on the differences between the applied VR modalities in terms of effect (in this case, positive) was found for the duration of nausea (NAUS DUR , Part.Eta2 = 47.9 %, p = 0.006), followed by the intensity of nausea (NAUS INT , Part.Eta2 = 27.4 %, p = 0.031), and finally the intensity of the feeling of nausea (NAUS QT , Part.Eta2 = 36.2%, p = 0.023, Table 2).These findings indicate that C-Infinity has the greatest positive effect on reducing the duration of nausea, followed by the intensity of nausea, and then the intensity of the feeling of nausea when compared to the Gamepad.

Non-statistically significant results (p-value > 0.05)
Regarding the metabolic effect of the applied VR modalities, although no statistically significant differences were found, it should be noted that C-Infinity usage resulted in a decrease in lactate levels by 8.4 %, whereas Gamepad usage resulted in increased levels of lactate by 8.9 % (Table 2, Part.Eta2 = 12.4 %, p = 0.217).These results might indicate the greater activation of the cardiovascular system in the low aerobic stress zone due to the greater physical activity (HR around 90.0 bpm, Table 2) during the use of C-Infinity VR modality.

Comparison between c-infinity and Gamepad modalities
The results of the inter-test differences determined between the initial and final testing, for statistically significant variables are shown in Fig. 4. The differences between C-Infinity and Gamepad modalities are presented as the average relative percentage difference across samples between changes in measured variables (between the initial and final testing).This is a practical numerical difference between C-Infinity and Gamepad usage on the neuromuscular, metabolic, and cardiovascular outcomes.

Discussion
VR has become an essential technology in gaming, industrial and military training as well as in education, medicine and more.However, half or more of the users can experience VIMS in VR [29], manifesting as dizziness, nausea and disorientation due to the discrepancy between the visual and vestibular input of VR users.Our study introduces the C-Infinity controller to reduce the VIMS symptoms, promoting a more immersive and comfortable VR experience.This study showcases a promising approach for mitigating motion sickness in VR, evidenced by the notably less nausea in users of META Quest 2 headset with the C-Infinity interface.
Our study found that only 3 min spent in VR can negatively impact the neuromuscular function of healthy adults.Specifically, muscle strength decreased by 5.2 % in C-Infinity users and 8.5 % in standard gamepad users (Table 1).However, the decline in muscle strength in C-Infinity users was 36.5 % less compared to Gamepad users.Despite this reduction, based on average measurements F max _SUM and RFD max _SUM, as well as maximal muscle strength and maximal explosive muscle force measurements, the average force output of our participants remained within the normal range for physically fit adults, which is in general between 910 and 1084 N and 5763 -7182 N/s, for F max _SUM and RFD max _SUM, respectively [12,18].It is also noteworthy that VR seemed to compromise the maximal explosiveness more than the maximal muscular strength (Table 1, Partial Eta 2 = 9.1 % vs 8.2 %, respectively).These neuromuscular characteristics of humans that can be quantitatively assessed and used for non-invasive data collection before and after VR usage [19,20,25,30] are essential for understanding how VR alter physical abilities.Although these findings are not statistically significant, likely due to the limited number of test subjects, they suggest a positive trend where C-Infinity may help mitigate VR's adverse effects on neuromuscular function.
Furthermore, C-Infinity interface significantly alleviated what we consider a critical aspect of VR experience, the user's subjective sensation and symptoms of nausea, including intensity, duration, and quantity (Table 2, p = 0.031, 0.006 and 0.023, respectively) compared to standard Gamepad.The most substantial improvement was in the duration of nausea (47.9 %), followed by the strength (quality) of nausea (36.2 %) and then the intensity of nausea (27.4 %).These improvements underscore the significant advantage of C-Infinity for VR users equipped with Quest 2 headsets.
Our working hypothesis regarding the mechanism behind the C-Infinity device's effectiveness in the generation of sensation for forward movement is schematically illustrated in Fig. 5.We theorize that the slight pressure generated with the users' fingertips on the sensor of the C-Infinity controller generates a faint signal in the somatosensory cortex of the user, with some "noise" generated in the motor cortex region for forward movement.This activation of C-Infinity controller sensor generates forward movement in real-time in VR, resulting in the immediate visual conformation of the initiated movement for the user in VR, which subsequently results in a more natural sensation of forward locomotion and reduced nausea.
In regards to the activation of the cardiovascular system measured by HR, there was a statistically larger increase in HR after using the VR with C-Infinity compared to the standard Gamepad, at the level of p = 0.046, Partial Eta 2 = 6.2 % (Table 2, Fig. 3).Specifically, the HR increased by 22.6 % with C-Infinity, versus a 17.8 % increase with the Gamepad.This variation in cardiac activation could be attributed to the different stature and motor activity performed by the subjects; The standing position with dynamic stabilization of the lower limbs on the foot platform, as well as active rotations to the left or to the right by the trunk rotator muscles with the simultaneous constant activation of the arms during the command to move forward or backward using C-infinity, likely activated the muscle groups responsible for given movement activities.Such activity likely intensifies the energy expenditure during VR C-infinity activity, which provoked a significnat increase in HR.We believe this is a direct result of increased general physical activity and physical engagement when using C-Infinity compared to the standard Gamepad.
For more conclusive insights, future experiments with a larger cohort are needed in order to obtain statistically significant results for neuromuscular measurements and allow for extended VR sessions.We also believe that repeated C-Infinity utilization could help highly sensitive users to adapt easier to locomotion in VR and thus allowing them to safely utilize VR for training and/or other activities.
Additionally, we advocate for special attention to VR for its safety and accessibility.Specifically, in therapeutic applications, alternatives to locomotive tasks need to be devised for individuals who cannot use treadmills or similar devices due to physical restrictions or limited space availability.Developing methods to simulate movements in VR that feels natural is crucial for reducing motion sickness and enhancing user comfort.Moreover, a deeper understanding of the short and long-term impact of VR usage at work, in school, in the military, or in gaming places on neuromuscular functions of users is essential, as these can influence bodily functions and reactions in real-life settings post VR exposure.
In closing, VR heralds a transformative era across diverse sections, including education, industrial training, medicine, construction, military, and entertainment.To fully leverage VR's enormous potential, it is essential to address challenges and offer novel solutions to prevent the development of VIMS and the spatial constraints often required by VR setups.Whole body controllers such as C-Infinity represents innovative strides towards offering a more natural sensation of locomotion and reduction of nausea in VR users, paving the way for the broader adoption and enjoyment of VR technology in the future.

Conclusions
In summary, our research indicates that C-Infinity controller can offer a more enjoyable and pleasant time in VR with significantly reduced sensation of nausea.This innovative controller, which engages the whole body for locomotion in VR, not only enriches the user's interaction with VR, but can also promotes increased physical and cardio activity.For users who traditionally spend extended periods seated while consuming VR content, the C-Infinity controller may offer a beneficial alternative, potentially help reducing adverse impacts of the prolonged sedentary lifestyle.

Limitations and future work
This preliminary study's findings are promising but limited by the small sample size and focus on short-term VR exposure.Future research should investigate the long-term efficacy of C-Infinity and its impact on a broader population to improve our understanding of VR usage on neuromuscular functions of users during and after VR usage.

Fig. 5 .
Fig. 5. Schematic presentation of the proposed mechanism for the generation of sensation for forward movement in C-Infinity.(A) Slight pressure is generated with fingertips on the sensor of C-Infinity controller that generates a faint signal in the somatosensory cortex with some "noise" generated in the motor cortex region for forward movement.(B) Activated sensor on C-Infinity generates forward movement in real-time resulting in the visual conformation of the initiated movement for the user in VR.
isometric strength indicator calculated as a summarized L + R F max value (F max _SUM), expressed in Newtons (N); 2. Maximal achieved rate of force development as an indicator of explosive voluntary strength (RFD max ) with the right (R) and left (L) hand, as well as overall body explosive isometric strength indicator calculated as a summarized L + R RFD max value (RFD max _SUM), expressed in Newtons per seconds (N/s); 3. Time to reach maximum voluntary force as an indicator of CNS full muscle activation potential for reaching maximal tension, i.e.Lactate concentration in rest (LA rest ) and after three minutes of VR activity recovery (LA peak ) from finger capillary blood and expressed in millimoles per liter (La in mmol/L), as metabolic acidosis measure; 2. HR at rest (HR rest ) and peak (HR peak ) was expressed in beats per minute (bpm), as functional exertion of the cardiovascular system measure ]: 1.Maximal achieved voluntary muscle force as an indicator of maximal strength (F max ) with the right (R) and left (L) hand, as well as overallFig.2. Screenshots from the VR content of an underground garage used in this study.body

Table 1
Comparison of neuromuscular function between C-Infinity and Gamepad modalities, with measured variables on the subgroup of responders (MEAN ± SD) and differences of muscle isometric strength (HG) before (Initial) and after (Final) VR protocol usage.ΔCITest and ΔGpTest are the average delta values across samples, for each corresponding variable, for C-Infinity and Gamepad modalities accordingly.

Table 2
Comparison of nausea between C-Infinity and Gamepad modalities, with measured cardiovascular, metabolic, and nausea variables on the subgroups of responders (MEAN ± SD) and differences of the variables before (Initial) and after (Final) VR protocol usage.ΔCITest and ΔGpTest are the average delta values across samples, for each corresponding variable, for C-Infinity and Gamepad modalities accordingly.The statistically significant variables (p-value < 0.05) are marked with asterisk.