# Seasickness and partial peripheral vision obstruction with versus without an artificial horizon

Camille de Thierry de Faletans, Maxime Misericordia, Jean-Marc Vallier, P

Duché, Eric Watelain

► To cite this version:

Camille de Thierry de Faletans, Maxime Misericordia, Jean-Marc Vallier, P Duché, Eric Watelain. Seasickness and partial peripheral vision obstruction with versus without an artificial horizon. Dis- plays, 2024, 85, pp.102851. 10.1016/j.displa.2024.102851. hal-05030321

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# Seasickness and partial peripheral vision obstruction with versus without an artificial horizon☆

Camille de Thierry de Faletans*, Maxime Misericordia, Jean-Marc Vallier, Pascale Duché, Eric Watelain

*Laboratory « Jeunesse – Activité Physique et Sportive- Santé » (J-AP2S), UR 201723207F, University of Toulon – TOULON, France*

## ARTICLE INFO

**Keywords:**

- Countermeasures
- Dynamic feedback
- Visual cues
- Motion Sickness
- Boat simulator

## ABSTRACT

Motion sickness (MS) is common when subjects are exposed to unfamiliar motion and affect individuals during travel. This study examines the immediate effect of two visual devices, in the form of glasses, on MS symptoms and associated physiological effects. The hypothesis is that peripheral vision obstruction reduces MS and that an additional beneficial effect could be observed when it is combined with an artificial horizon. Fifteen subjects with moderate to severe susceptibility to MS were exposed to a boat simulator in three conditions. Symptoms were assessed immediately after exposure. Time spent in the simulator, heart rate, and temperature were also recorded. The intensity of symptoms at the end of the experience did not differ, but time spent in the simulator before the onset of symptoms was significantly longer with peripheral vision obstruction (+36 %) and with both techniques combined (+40 %) than in the control condition. No difference was observed between the combined condition and peripheral vision obstruction alone. The glasses device used in this study (with or without an artificial horizon) delays the onset of symptoms. Further research is needed to confirm the mechanism that explains the benefits and to evaluate these effects during prolonged exposure to MS-inducing stimuli or after a period of familiarization with the device.

## 1. Introduction

Motion Sickness (MS) is a normal and universal physiological reaction in healthy people in response to unfamiliar physical movement [1]. It differs from Visually Induced Motion Sickness (VIMS), which is solely produced by visual movements [2]. These symptoms range from general discomfort to vomiting, including nausea, gastrointestinal discomfort, headaches, dizziness, drowsiness, disruption of thermoregulation, and alteration of wakefulness [3]. Physiologically, we generally observe a decrease in core temperature [4,5] and an increase in Heart Rate (HR) [6–8], although some studies have also noted HR decrease during motion exposure [9,10].

The most widely accepted theory to explain MS is the sensory conflict theory. According to this theory, MS is due to a mismatch between the information received about body movements by the various sensory receptors (visual, vestibular, and proprioceptive) and the subject's internal model, developed by previous experiences [11,12]. The degree of discrepancy between what is perceived and what is expected plays a key

role in determining the severity of MS. When the conflict is too great, MS symptoms appear. A variant of this theory, the subjective vertical theory, suggests that MS is caused by a conflict between the subjective vertical perceived by sensory systems and the subjective vertical estimated based on experience [13]. Prothero et al. proposed a related version where sensory cues form internal models of what is motionless, called rest frames. In this case, MS results from the inability to choose one rest frame over another based on perceptual cues [14]. Finally, the instability theory by Riccio and Stoffregen is an alternative to the sensory conflict theory. They propose that postural instability precedes and is necessary for the onset of MS. Sensory systems constantly seek to maintain postural stability in different environments. In a moving environment, the body tries to correct and minimize deviations from normal postural states. If instability persists, symptoms arise.

The most common solution to reduce MS symptoms is still through medication (anticholinergics and antihistamines), though they can cause side effects like drowsiness, headaches, and difficulty concentrating [15]. Habituation to provocative motion is also effective [16],

<footnote>* This paper was recommended for publication by Prof Guangtao Zhai.</footnote>

<footnote>* Corresponding author.
E-mail address: watelaindeth@univ-tln.fr (C. de Thierry de Faletans).</footnote>
but requires significant time and is specific to certain stimuli. Recently, research has focused on developing devices that provide additional sensory cues about motion to reduce sensory conflict. These devices aim to provide information on body movements to reduce discrepancies between visual, vestibular, or proprioceptive information. They can, for example, provide real-time or anticipatory tactile [17,18] or auditory [19] cues about the movements experienced by the subject in a vehicle.

At the visual level, motion cues have been tested by adding additional elements that move with the vehicle's movements on screens [20,21] or by projecting the road view onto a screen when outside visibility is limited [17,22,23]. More recently, researchers have tested devices that provide information in the peripheral vision to keep the central vision free for other tasks. These devices used LED strip systems inside the vehicle with lighting that adjusts according to the vehicle's movements [24–26]. Studies have shown, for example, that such light strips can create an artificial horizon, delaying the onset of MS symptoms when exposed to a boat simulator [25]. Adding an artificial horizon referenced to the Earth provides participants with information about gravity and the orientation of their bodies relative to it. For instance, Rolnick and Bles, found that subjects experienced fewer MS symptoms with an outside view of the simulator or a projected artificial horizon compared to no visual reference to the Earth [27]. In addition, Feenstra et al. achieved a 37% reduction in MS by adding Earth-referenced visual cues in virtual reality [28]. Furthermore, Tal et al., observed a significant decrease in MS intensity when the visual display closely matched the simulator's motion [29].

On the other hand, reducing the field of vision has also been effective in reducing MS. Bonato et al., showed that reduced central visual acuity worsens MS by increasing peripheral visual information about movements that conflict with the vestibular system [30]. Conversely, Hussain et al., found that lowering peripheral visual acuity reduces MS by decreasing visual movement information [31]. Other authors such as Lin et al., studied different visual field sizes (60°, 100°, 140°, and 180°) and observed that larger fields increased MS severity [32]. These results reproduce those observed by Seay et al., on fields of vision of 180° to 60° [33]. Thus, the significant role of vision in MS suggests it is an ideal target for MS reduction devices.

All these techniques present interesting results, but none completely eliminates or prevents all symptoms. Previous studies have shown that combining different techniques can have additional benefits. For instance, Bos demonstrated that combining head vibration and mental distraction reduced MS by 39%, compared to 25% and 19% for each technique alone. Similarly, Gálvez-García et al., found that combining white noise and galvanic cutaneous stimulation reduced MS by 73%, compared to 50% and 48% for each technique alone [19]. While Bohrmann et al., and Diels et al., did not find their LED systems effective alone but they observed reduced symptoms when combined with an outside view or improved vehicle comfort [24,26]. These findings suggest that combining methods might be more effective than using a single approach.

The current study aimed to evaluate the combined effect of peripheral vision obstruction and artificial horizon on MS using a glasses device. The glasses have four lenses with liquid that moves with head movements (for one condition) or does not move (for another). The liquid provides real-time visual feedback as an artificial horizon referenced to the Earth. Given that boats are the mode of transportation with the highest prevalence of MS [34], subjects were exposed to a boat simulator in three conditions: without a device (C), with peripheral vision obstruction (P), and with both peripheral vision obstruction and an artificial horizon (P+AH). The hypothesis is that peripheral vision obstruction reduces MS by inhibiting or delaying the onset of symptoms, and combining both techniques has an additional beneficial effect on reducing MS.

# 2. Methods

## 2.1. Participants

Fifteen participants (11 women) aged between 19 and 54 years (29.6 ± 12.4 years) were recruited voluntarily from university faculty and students. Inclusion criteria for the study required participants to have no vestibular, balance, or motor disorders, to possess normal or corrected to normal vision, and to attain a total score on the MS Susceptibility Questionnaire Short form (MSSQ-S, [35]) higher than 11.3 (50th percentile). The total MSSQ-S provides a susceptibility score for MS ranging from 0 (no symptoms) to 54 (severe symptoms in all modes of transport). Subjects were required to abstain from medication, alcohol, or drugs for the preceding 24 h. Participants provided voluntary and informed consent and had the right to withdraw from the experiment at any time. The National Ethics Committee for Research in Physical Activity Sciences approved the experiment under IRB 00012476-2021-16-04-104, and all procedures adhered to the principles of the Declaration of Helsinki.

## 2.2. Apparatus

The simulator of seasickness (de Thierry de Faletans et al., in review) comprises a rigid boat (W:1*L:2*H:0.30 m), with an enclosed cabin (W:1*L:1.40*H:1.20 m) on top of it to totally obstruct the field of view (Fig. 1). It is positioned in a reinforced pool (W:1.80*L:3.80*h:1.25 m). Inside the boat, 4 strips of 1-meter white LED lights were installed to illuminate the cabin and reproduce the interior of a boat. The subject was seated on a bench 2/3 behind the axis of rotation and without a backrest or headrest. The subject's head was oriented toward the interior of the boat, facing the axis of rotation. The boat underwent a periodic tilting motion along the transverse axis, moving forward and then backward (pitch) at a frequency of 0.1 Hz. This motion involved alternating lifting and lowering of the front and rear of the boat, with an amplitude of 22.5 cm relative to the horizontal position. This corresponds to a pitch angle of 12.7° relative to the boat's horizontal position and a total vertical distance traveled of 45 cm. A camera was placed in the boat to monitor the subject throughout the experiment. Internally, the boat features a schematic Visual Analog Scale (VAS) from 0 to 10 and a list of the ten most common symptoms of MS (anxiety, general discomfort, hypersalivation, sensation of heat, headaches, drowsiness, gastric discomfort, nausea, fatigue, and dizziness, Fig. 1). These 10 symptoms belong to the 4 symptom categories described by Cha et al., [36] and correspond to a compilation of the Pensacola Diagnostic Index [37], the Simulator Sickness Questionnaire [38], and the Motion Sickness Assessment Questionnaire [39].

Two types of devices were used. In the condition P+AH, the subjects wore the Boarding Glasses, produced, distributed, and patented by Boarding Ring (Fig. 2). These glasses are composed of 4 lenses, 2 in the front and 2 on the sides. These lenses are half-filled with blue liquid situated at the periphery of the visual field, which is sensitive to head rotation. This liquid is composed of an organic oil whose density and viscosity properties are similar to those of water. This, combined with a small ring cross-section, should reduce sloshing. In the two front lenses, the liquid moves around the eyes in the frontal plane (left-right) and in the two lenses on the sides, it moves in the sagittal plane (front-back). The presence of liquid around the lenses requires an extra thickness of the frames and lens contours, resulting in a 25% horizontal obstruction of the field of vision and an 18% vertical obstruction. This means that glasses reduce monocular vision by obstructing the peripheral field of vision by around 25° on each side (Fig. 2). For condition P, identical glasses were used, but the inside of the lenses were empty and were colored in the same way as the liquid normally present, to represent the liquid fixed and insensitive to head movements.
<figure><img src="image_3.png" /><figcaption>**Fig. 1.** Photographs of the boat travel simulator, with an interior view of the subject in position. The red dotted arrow represents the boat's axis of rotation, inducing a pitching motion at an angle of ± 12.7° beside horizontal (see for more details on the simulator conception de Thierry de Faletans et al. 2024, In review). On the right is the list of symptoms that can be used as stop criteria and the VAS presented to help the subject rate the intensity of these symptoms between 0 and 10 during the simulation. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

## 2.3. Measurements

The maximum duration of the simulation is 10 min. The simulator stops if the subject meets the stop criteria or upon reaching the maximum exposure time limit. Two stop criteria were established: participant reporting (i) one symptom scoring 5 or higher, (ii) 3 symptoms scoring higher than 1 on the 0 to 10 symptoms intensity scale that was displayed in the boat (Fig. 1). Subjects informed about the stop criteria and were asked to mentally and continuously estimate the intensity of the symptoms they felt while being in the simulation. Should subjects meet either criterion, they were instructed to notify the experimenters verbally, prompting immediate cessation of the simulation. The duration spent in the simulator before symptom onset, as defined by the stop criteria is measured in seconds from the start of the simulation until the stop. At the end of the simulation, symptom intensity was evaluated in writing using 10 independent VAS, assessing the following symptoms: anxiety, general discomfort, hypersalivation, sensation of heat, headaches, drowsiness, gastric discomfort, nausea, fatigue, and dizziness. Subjects were instructed to mark a line on the VAS between 0 and 10, corresponding to their perceived intensity of each symptom at the end of the simulation. The mean values and standard deviations of the 10 symptoms were calculated for each subject. Core temperature was assessed using an infrared forehead thermometer (Braun BNT 400), which measures skin energy emission at the forehead and converts it

into an approximate body temperature value. Continuous HR monitoring was conducted throughout the simulation using an HR monitor (Polar H10). Throughout the simulation, subjects viewed a cartoon aimed at directing their gaze and simulating engagement in a task unrelated to the boat's movement. An iPad Pro 12.9" positioned in landscape mode was used and placed 50 cm from the subjects' eyes. The subject's gaze was directed 15° downward from the anatomical position, and the visual field occupied by the screen, from the observer's perspective, was approximately 24°. The glasses worn by the subject only obstructed a part of the peripheral vision, which means that this obstruction did not affect the vision of the video screen. Copyright-free, emotionally neutral videos were selected for each condition to prevent any influence on symptoms or physiological measures. The videos, animated films available on YouTube, were in color and without dialogue, depicting short adventures of characters. There were no videos with first-person perspectives or scenes of traveling in a vehicle. Five questions were asked after the simulation to confirm subjects' engagement with the video, focusing on factual elements from the video, such as the color of the main character's hat, eliciting open-ended responses like "red". Out of 10 potential questions per video, 5 were selected for each subject based on the duration of the sequence viewed by the subject during the simulation. Correct answers were assigned 1 point each, and the total score for the 5 questions was calculated. The difference in the number of correct answers between the conditions also allowed
<figure><img src="image_4.png" /><figcaption>**Fig 2.** Illustration of the glasses used. **Panel A** is a schematic representation of how Boarding Glasses works. The liquid in the lenses moves with the movements of the head to form an artificial horizon referenced to the Earth. **Above:** The illustration shows the movements of the liquid during movements in the sagittal plane. **Bottom:** in the frontal plane. In the experimental situation presented in this study, only movements in the sagittal plane are induced. **Panel B** illustrates the difference in liquid action in the glasses. **Above:** the real Boarding Glasses with the liquid moving with movements. **Bottom:** the glasses with the liquid remaining fixed. **Panel C:** Schematic representation of the human horizontal field of vision with foveal, binocular, and monocular vision regions. The black triangle represents blind zones induced by the frames and contours of the glasses. These gray areas result in a 25° reduction of the peripheral field of view, nearly halving monocular vision.</figcaption></figure>

observation of whether the artificial horizon and/or the obstruction of the field-of-view interfered with the subject's performance of a viewing task.

## 2.4. Procedure

Subjects received detailed instructions about the experiment procedures and the boat movements they would encounter. Each subject was confronted with three distinct conditions: control (C), peripheral vision obstruction (P), and peripheral vision obstruction with artificial horizon (P+AH). The order of conditions was randomized across subjects. Sessions for the three conditions were spaced at least one day apart to allow for full recovery from any simulator-induced symptoms. All sessions took place at the same time of day to mitigate potential diurnal effects. Subjects were not provided with information regarding device operation, and no distinctions were made between conditions during the instructions. Following the instructions, subjects were fitted with the HR monitor. HR was recorded for 5 min at rest and continuously from the beginning to the end of the oscillations. Similarly, the temperature was measured first at rest, then a second time just before the start of the oscillations, and finally at the end of the simulation. Before the oscillations started, subjects were given a tablet to watch the video, and the device was adjusted to the condition. Subjects were instructed to look at the tablet in front of them and not to move during the simulation. The pitching movements then began. simulation was initiated, exposing subjects to pitch motion at a frequency of 0.1 Hz and an amplitude of 45 cm. The simulation stopped if subjects met the stop criteria or upon reaching the maximum exposure time of 10 min. At the end of the simulation, subjects disembarked the boat and rated the intensity of experienced symptoms using 10 VAS. They also answered five comprehension questions about the video. Ambient temperature, noise levels, and brightness were controlled throughout the experiment.

## 2.5. Statistical analysis

The results are presented as average and standard deviation. The average HR is calculated for the 5-minute rest period and 30-second interval at the start and end of the oscillations. As the time spent in the simulator and the intensity of the symptoms did not meet the conditions of normality, the statistical significance of the differences

between conditions was determined by Friedman tests, followed by Conover post hoc tests. For the temperature and HR data, 2-factor repeated measures ANOVAs were carried out with the condition factor (C, P, P+AH) and the time factor (rest, start, end) as well as Tukey's post hoc. The significance level was set at *p* < 0.05 (*<0.05*, ** <0.01, ***<0.001). Effect sizes based on standardized differences between mean scores were calculated to examine the magnitude of such differences. Effects size was calculated using Eta squared (η²) interpreted as 0.01 small, 0.06 medium, and 0.14 large for parametric data and using Kendall's W interpreted as 0.1 small, 0.3 medium, and 0.5 large for non-parametric data.

## 3. Results

Subjects had a mean MSSQ-S total raw score of 37.9 ± 8.1. This represents an MS susceptibility interval covering total raw scores between 16 and 50, corresponding to percentile scores between 70 to 100 % [35].

### 3.1. Time in the simulator

Across all subjects, none completed the 10-minute simulation in condition C, 3 subjects completed the simulation in condition P, and 5

<caption>**Table 1**</caption>

Distribution of the number (percentage) of subjects in the 3 conditions who completed the 10-minute simulation or stopped before the end because they reported symptoms that corresponded to the simulation stop criteria (3 symptoms evaluated with a score greater than 1 out of 10 or 1 symptom greater than or equal to 5 out of 10).

<table><thead><tr><th rowspan="2">Time of simulation</th><th rowspan="2">Stopping criteria</th><th colspan="3">Conditions</th></tr><tr><th>C (%)</th><th>P (%)</th><th>P+AH (%)</th></tr></thead><tbody><tr><td rowspan="2">Stop simulation before end</td><td>3 symptoms > 1</td><td>11 (73 %)</td><td>10 (67 %)</td><td>9 (60 %)</td></tr><tr><td>1 symptom ≥ 5</td><td>4 (27 %)</td><td>2 (13 %)</td><td>1 (7 %)</td></tr><tr><td>10 min of simulation</td><td></td><td>0 (0 %)</td><td>3 (20 %)</td><td>5 (33 %)</td></tr></tbody></table>

C: control, P: peripheral vision obstruction, P+AH: peripheral vision obstruction with artificial horizon.
subjects completed it in condition P+AH (Table 1). Two subjects completed the 10 min in both P and P+AH conditions. The time spent in the simulator according to the conditions was significantly different ($\chi^2 = 8.414, p = 0.015, W=0.280$). Subjects stayed longer in the simulator in the P+AH condition than in C ($p = 0.015$) and in the P condition than in C ($p = 0.022$) but there was no difference between condition P and P+AH ($p = 0.854, C=331.3 \pm 123.3, P=452.6 \pm 127.9, P+AH=465.1 \pm 151.7, Fig. 3).

## 3.2. Symptoms and video questions

Regarding the stopping criteria of the simulation: (i) in condition C, 73 % of the subjects requested the simulation to stop for 3 symptoms greater than 1, and 27 % for at least one symptom greater than or equal to 5; (ii) in P condition, 67 % requested the simulation to stop for 3 symptoms greater than 1, and 13 % for at least one symptom greater than or equal to 5; (iii) in P+AH condition, 60 % requested the simulation to stop for 3 symptoms greater than 1, and 7 % for at least one symptom greater than or equal to 5 (Table 1). Among the subjects who asked for the simulation to be stopped before the end, the symptoms most frequently given as stopping criteria in the three conditions were nausea and headache. There was no significant difference between conditions for symptom scores ($\chi^2 = 1.733, p = 0.420, W=0.058; C=4.55 \pm 1.6, P=4.02 \pm 2.5, P+AH=4.01 \pm 1.9; Fig. 4$). The number of correct answers to the video questions did not vary significantly according to the conditions ($\chi^2 = 1.720, p = 0.423, W=0.057; C=2.3 \pm 1.3, P=3 \pm 1.2, P+AH=2.7 \pm 1.6$).

## 3.3. Physiological parameters

For HR, there was a significant effect of time (F (2,24) = 33.418, $p < 0.001, \eta^2 = 0.320, Fig. 5) but there was no effect of condition (F (2,24) = 1.259, $p = 0.302, \eta^2 = 0.032$) or interaction (F (4,48) = 2.694, $p = 0.076, \eta^2 = 0.041$). Subjects had a higher HR at the end of stimulation

<figure><img src="image_5.png" /><figcaption>**Fig. 3.** Individual values of the time spent in the simulator according to the conditions: Control in green (C), with obstruction of peripheral vision in blue (P), and with an artificial horizon in addition to obstruction of peripheral vision in red (P+AH). The squares represent the means for each condition. \* *p*-value < 0.05; ns no significant difference; s seconds. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

than at the beginning ($p < 0.001$), at the end than at rest ($p < 0.001$), and at the beginning than at rest ($p = 0.003$). For temperature, there was no significant condition effect (F (2,24) = 0.369, $p = 0.695, \eta^2 = 0.017$, time effect (F (2,24) = 1.588, $p = 0.225, \eta^2 = 0.022$), or interaction (F (4,48) = 2.403, $p = 0.063, \eta^2 = 0.038, Fig. 5).

# 4. Discussion

This study aimed to test the effect of peripheral vision obstruction on MS, and the potential additional effect of combining two techniques impacting the visual system, i.e. peripheral vision obstruction and the addition of an artificial horizon, referenced to the Earth, which adjusts in real-time to head movements, on the MS. Peripheral visual obstruction has been associated with a reduction in seasickness, but we found no evidence that combining it with artificial horizon provided any instantaneous additional benefit on the reduction of seasickness.

## 4.1. Peripheral vision obstruction

Peripheral vision obstruction (P) increases the time to onset of symptoms as defined by the stopping criteria. 80 % of subjects increased their time in the simulator in the P condition (+36 %) compared with the control condition. The peripheral visual system, associated with low visual acuity, is sensitive to environmental movements [30,32]. In contrast, the central visual system, with high visual acuity, specializes in detail processing and object identification. Thus, disrupting central vision by adding visual blur increases MS [30], while reducing peripheral vision reduces MS [31] by decreasing visual motion information in conflict with other sensors such as the vestibular system [32,33,40]. In this study, the time to symptom onset increased in P condition, consistent with Hussain et al., [31]. This time increase was equivalent to a factor of 1.36 for a 25° visual field obstruction on each side. This effect is slightly lower than previous studies, such as Keshavarz et al., which showed a 2.2 reduction in MS severity for over 80 % visual field reduction and 1.9 for over 70 % reduction [41]. Lin and al., established a positive correlation between visual field size and MS severity [32]. Thus, the smaller visual obstruction in this study and the specific part of the peripheral vision obstructed (obstructs peripheral vision without suppressing the farthest peripheral zone) may explain the difference in observed effects.

## 4.2. Combining the peripheral vision obstruction with the addition of an artificial horizon

In the P+AH conditions, subjects also spent more time in the simulator. 80 % increased their time (+40 %) compared to the control condition. In the literature, providing additional visual information about movement or reducing peripheral optic flow limits sensory mismatch, helping the central nervous system perceive less discordant information. However, no difference was observed between the P and P+AH conditions. Six subjects decreased their time in the simulator between the two conditions, two spent 10 min in both and seven increased their time in the P+AH condition compared to P (Fig. 3). This suggests that peripheral vision obstruction, combined with the artificial horizon created by the liquid present in the glasses, does not seem to have any additional beneficial effect on reducing MS during the initial phase of symptom onset compared with peripheral vision obstruction alone.

The beneficial effects of an artificial horizon have been documented in the literature [25–27,45,47], as well as in a similar study where a dynamic artificial horizon reduced MS in 86 % of subjects (+46 % additional time in the simulator [23]). However, previous studies have used the external view of the simulator, image, or horizontal line projection to create an artificial horizon [27–29,46,48]. In the present study, we tested an artificial horizon created by a liquid, which allows for a faithful representation of the horizon during slow rotations. In contrast, during rapid head rotations or translations, the movement
<figure><img src="image_6.png" /><figcaption>Fig. 4. Average and standard deviation of the score on Visual Analog Scale (VAS; 0 to 10) by symptoms according to the conditions: Control (C), with obstruction of peripheral vision (P), and with an artificial horizon in addition to obstruction of peripheral vision (P+AH).</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>Fig. 5. Average and standard deviation of temperature (graph A) and heart rate (graph B) measurements, according to the condition. Control (C) represented in green and stars; with obstruction of peripheral vision (P) represented in blue and squares, with artificial horizon in addition to obstruction of peripheral vision (P+AH) represented in red and triangles. \*\* p-value < 0.01, \*\*\* < 0.001; C° Celsius degree; bpm beats per minutes. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

information may be less accurately conveyed due to the inertia of the liquid or potential sloshing effects. In these conditions of movement, it seems more appropriate to present an artificial horizon in another form. Thus, in our case, although the subjects were instructed not to move and the oscillation was slow, the liquid may have created a less stable artificial horizon than those used in previous studies, which were perhaps closer to the earth's horizon [27–29,46,48]. This could contribute to explaining the absence of difference between the two test conditions.

Sensory conflict theory describes conflict at multiple levels: between different sensory systems, within a sensory modality, and between

perceived and expected models of movement [11,12]. Unlike Gálvez-García et al., or Bos who combined two techniques acting on different sensory modalities (tactile/auditory and tactile/cognitive) [19,42], this study tested two techniques acting only on the visual modality. For example, the latter had no impact on intra-vestibular conflicts, between angular vestibular inputs (semicircular canals) and linear inputs (otolith organs) [43]. In addition, studies on blind or vestibulopathic patients suggest vision plays only a partial role in MS. Individuals with total labyrinthine deficiency are immune to MS [44,45], while the absence of visual information in those with a functional vestibular system reduces
does not eliminate symptoms [46,47]. A study on blind subjects revealed no difference between blind and sighted subjects in MS susceptibility, concluding that vision is not essential but secondary in the genesis of MS [47]. It is therefore possible that to achieve an additional beneficial effect on reducing MS, a combination of techniques acting on different sensory modalities may be more effective, as they can intervene at different levels of sensory conflict. It is also possible that the subjects need time to acclimatize to correctly use the information provided by the artificial horizon formed by the glasses, which the short duration of the simulation did not allow them to do.

Finally, given the difference observed with the control condition and the similar effect observed in both conditions with glasses, it is not possible to exclude the possibility of a placebo effect that could have delayed the onset of symptoms, without this being linked to the technical characteristics of the glasses themselves. Unlike some studies where the artificial horizon may go unnoticed if the subject does not pay attention (external view of the simulator, LED strip), the device tested here is placed directly on the face by the subject itself. Thus, although the experimental conditions were not explained to the subjects in advance, they were aware of the study's topic and could not ignore the fact that the glasses were being worn. This may have constituted a form of distraction or altered the subject's comfort due to the physical presence of the glasses, which may have had a greater psychological impact than devices integrated into the subject's environment.

### 4.3. Limitations and perspectives

Concerning the symptoms, the lack of difference between the three conditions suggests that subjects adhered to the stopping criteria. Although they spent more time in the simulator with the devices, they requested the simulation to stop when symptoms reached the same intensity in all three conditions. This indicates that the devices delay symptom onset rather than completely eliminate them. However, the low intensity of symptoms (3 symptoms above 1 out of 10) may also explain the lack of difference. This intensity, while sufficient to detect initial MS signs, might not be high enough to show significant changes between conditions. This may also explain the lack of difference in physiological variables. In addition, the use of questionnaires presents the limitation of relying on self-reported data.

Finally, although the simulator used can reproduce a navigation situation and induce real seasickness, it is important to note that the simulated situation differs from real navigation, particularly due to the absence of random variations in oscillations (both in frequency and amplitude) and movements in other axes of rotation (such as roll and yaw). Additionally, during a sea travel, it is rare for the subject to remain perfectly still.

Future studies should include a larger sample size, a more intense induction of symptoms, extended exposure to movement, and the use of symptom assessment scales such as the MISC (Misery Scale; [46]) to increase the likelihood of detecting significant differences in symptoms between conditions. Measuring symptoms over time and integrating physiological measures, such as heart rate variability and electrodermal activity, could provide a more comprehensive and objective evaluation of MS. Additionally, it would be valuable to test these glasses in real-life conditions, with a user feedback questionnaire to help to improve their ergonomics.

### 4.4. Conclusion

This study examined the effect of combining two visual techniques on MS symptoms and associated physiological. Both peripheral vision obstruction and a combination of peripheral vision obstruction with an artificial horizon delayed immediately the onset of MS symptoms as described in our arrest criteria. However, no additional benefit was observed by adding the artificial horizon compared with peripheral vision obstruction alone in the short simulated navigation tested in this

study. Further studies are needed to clarify these effects, but it seems preferable to combine techniques using different sensory modalities to optimize benefits.

## Funding sources

This study was supported by a doctoral research grant (recipient Camille de Thierry de Faletans) from the French Ministry of Higher Education, Research and Innovation. This research did not receive any specific funding from commercial companies.

## CRediT authorship contribution statement

Camille de Thierry de Faletans: Formal analysis, Investigation, Visualization, Writing – original draft. Maxime Misericordia: Formal analysis, Investigation, Data curation. Jean-Marc Vallier: Writing – review & editing. Pascale Duché: Project administration, Resources, Supervision, Writing – review & editing. Eric Watelain: Conceptualization, Funding acquisition, Methodology, Supervision, Writing – review & editing.

## Declaration of competing interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: [Equipment are for the laboratory not for an individual author reports equipment, drugs, or supplies was provided by Boarding Ring. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper].

## Data availability

Data will be made available on request.

## Acknowledgments

We would like to thank the Boarding Ring company (Ollioules - France), which specializes in designing motion sickness prevention systems, for their material contribution through the loan of Boarding Glasses.

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**Camille de Thierry de Faletans** is a PhD student at the J-AP2S laboratory, specializing in the interaction between physical activity, sport, and health in young people at the Faculty of Sport Sciences, University of Toulon, France. She works on motion sickness, particularly seasickness, and the development of non-drug countermeasures. She received her master's degree in cognitive science from Aix-Marseille University, France, in 2021.

**Maxime Misericordia** is a research assistant at the J-AP2S laboratory, specializing in the interaction between physical activity, sport, and health in young people at the Faculty of Sport Sciences, University of Toulon, France. He received his master's degree in sports science from the University of Toulon, France, in 2022.

**Jean-Marc Vallier** is a Professor and doctor in medicine at the J-AP2S laboratory, specializing in the interaction between physical activity, sport, and health in young people at the Faculty of Sport Sciences, University of Toulon, France. He received his Ph.D. in Sciences and Techniques of Physical and Sports Activities from the University of Paris, France, in 1995.

**Pascale Duché** is a Professor and director of the J-AP2S laboratory, specializing in the interaction between physical activity, sport, and health in young people at the Faculty of Sport Sciences, University of Toulon, France. She received her Ph.D. in Applied biological and basic sciences and psychology from the University of Clermont-Ferrand 2, France, in 1992.

**Eric Watelain** is a Professor at the J-AP2S laboratory, specializing in the interaction between physical activity, sport, and health in young people at the Faculty of Sport Sciences, University of Toulon, France. He received his Ph.D. in Sciences and Techniques of Physical and Sports Activities from the University of Lille 2, France, in 1999. He has published in the domains of posture, locomotion and sensory integration.