A Wearable Device Providing a Visual Fixation Point for the Alleviation of Motion Sickness Symptoms

Transcription

1 MILITARY MEDICINE, 180, 12:1268, 2015 A Wearable Device Providing a Visual Fixation Point for the Alleviation of Motion Sickness Symptoms Frederick Bonato, PhD*; Andrea Bubka, PhD ; Wesley W. O. Krueger, MD ABSTRACT Objectives: Motion sickness (MS) can be problematic for many military operations. Some pharmaceutical countermeasures are effective but can lead to side effects. Non-pharmaceutical countermeasures vary in effectiveness and can require time to be beneficial (e.g., desensitization). Previous research suggests that visual fixation can alleviate MS symptoms. In the current experiment we tested the effectiveness of a user-worn device that provides a visual fixation point that moves with the user. Methods: Fourteen subjects viewed the interior of a rotating optokinetic drum (60 /s) through a visor that displayed either a clear view of the scene (control) or the scene with a fixation point (experimental). After 5 minutes of viewing, symptoms were assessed using (1) the Simulator Sickness Questionnaire that yields four scores (total, nausea, oculomotor, and disorientation) and (2) a 0 to 10 MS overall scale. Results: Viewing the fixation point resulted in significantly lower scores for all measures. Control condition scores were as much as 400% higher than when the fixation point was viewed. Conclusions: A wearable device that presents a visual fixation point that moves with the user may reduce MS. The device s portability suggests that it may be suitable for some military operations, and additional research in the field is warranted. INTRODUCTION Motion sickness (MS) affects millions of travelers each year 1 including military personnel. Symptoms can include nausea, vomiting, headache, sweating, unsteadiness, feeling hot or cold, and disorientation. Riding in land vehicles, aircraft, and watercraft can all lead to MS. Therefore MS is a military concern. MS has accompanied vehicular travel for more than 25 centuries but still remains both a civilian and military problem. Regarding seasickness, Trumbull et al 2 reported vomiting incidence on military transport ships traveling across the Atlantic to vary from 8.5% to 22.1%. Handford et al 3 reported an even higher vomiting incidence of 34%. A survey of 699 men aboard U.S. Navy destroyers indicated 62% were at least occasionally sick, 10% often sick, and 13% almost always sick. 4 A study of the crew of two British Naval ships 5 revealed that 67% on one ship and 73% on the other had been seasick at some point during their career and 42% and 56%, respectively, experienced seasickness in the past 12 months. Money 6 reported that airsickness was much more common in military pilots compared to commercial pilots perhaps because of more stressful maneuvers. One study of U.S. Navy flight officers showed that MS affected 74% during basic training. 7 A Royal Air Force survey revealed that 39% of trainees experienced airsickness at some point in training and for 15% symptoms caused the disruption or *Montclair State University, 1 Normal Avenue, Montclair, NJ Saint Peter s University, 2641 Kennedy Boulevard, Jersey City, NJ Wesley W.O. Krueger, MD, 2632 Broadway, Suite 202, San Antonio, TX This article is based on a previous presentation at the Aerospace Medical Association, Anchorage, AK, May 9, doi: /MILMED-D abandonment of a flight. 8 Airsickness is also an issue for military non-pilot flying personnel such as gunners and electronic warfare officers, 9 bomber crews, 10 and student navigators. 11 Troops being transported by air are also at risk with incidence rates as high as 64% in one study of Mexican paratrooper students. 12 The most modern form of MS that can affect military personnel is simulator sickness. Simulator use for training has obvious benefits in terms of cost and safety; however, MS-like symptoms can result. Many military pilots have reported at least one symptom following simulator exposure. 13,14 In a study of Coast Guard aviators, 64% reported adverse symptoms during the first simulator flight and 39% did so during the last flight. 15 For helicopter pilots, 36% reported MS when training on a Blackhawk simulator. 15 MS countermeasures are available and vary in effectiveness. The antihistamines dimenhydrinate 16 and meclizine hydrochloride 17 can help alleviate symptoms but drowsiness is a common side effect. Scopolamine hydrobromide can also be effective 18 administered either in tablet form, via a transdermal patch, or using a nasal spray. 19 Side effects are common and can include dryness of the mouth, throat, and nasal passages. A common nonpharmaceutical attempt for treating MS entails bracelet-like devices worn around the wrist. It is claimed that stimulation of pressure points such as P6 act on the central nervous system to provide MS relief. Elastic versions simply employ pressure but more sophisticated devices provide electrical pulses. The effectiveness of pressure and stimulation of P6 is unclear. Although some studies support the effectiveness of acupressure 20 and electrical stimulation, 21 others failed to demonstrate any therapeutic effects on MS In this study, the effects of visual fixation on MS were tested in an optokinetic drum using conditions that are known 1268

2 to lead to visually induced MS symptoms Inconsistent sensory inputs (sensory conflict) are the most often cited factors associated with MS. 28 In vehicles, visual input to the brain often indicates that no self-motion is occurring but vestibular input does indicate the person is moving. The opposite is true in an optokinetic drum. A stationary observer sits inside the drum that rotates and simply views the drum s interior as it moves. Usually within seconds, illusory selfmotion (vection) occurs in the direction opposite that of the drum s rotation. Often within minutes, MS symptoms occur. Because both vehicles and optokinetic drums can lead to sensory conflict, it is not surprising that both can lead to MS symptoms. Hence, the optokinetic drum has become an important tool in MS research. This hypothesis can be safely and efficiently tested before more elaborate and often less controllable field studies are conducted. Stern et al 25 reported that eye fixation reduced MS. Webb and Griffin supported this finding 26 by showing that MS symptoms were reduced when subjects fixated on a stationary cross in an optokinetic drum. Also, conditions that entail both fixation and restricted field of view resulted in greater reductions in MS than restriction alone. 27 Visual fixation may serve to suppress optokinetic nystagmus 29 that has been hypothesized to result in abnormal eye muscle traction that can lead to visually induced MS and has been shown to be positively correlated with visually induced MS. 30 Visual fixation in laboratory studies has often involved an external fixation point that subjects are instructed to look at without moving their eyes. In this study a fixation point is presented to subjects with a user-worn see-through display. Hence, the fixation point can move with the subject. The goal of this study was to demonstrate the feasibility of a user-worn see-through display that could possibly serve as an effective counter-measure for MS. FIGURE 1. Front view of subject wearing the AdviTech device. The opotokinetic drum is shown in the raised position and was lowered before each trial. METHODS Subjects Human subjects approval was obtained in advance by the Saint Peter s University Institutional Review Board (IRB) and each subject provided written informed consent before participating in the study. Fourteen Saint Peter s University undergraduate students and staff voluntarily participated in the experiment (4 men, 10 women; mean age = 23.1 years). Persons were prescreened for visual, vestibular, neurological, and gastrointestinal abnormalities and only those with no known health problems were allowed to participate in the experiment. Subjects fasted for at least 2 hours before each trial. Graphic depiction of the fixation point seen through the wear- FIGURE 2. able visor. Equipment The subjects wore a see-through display (AdviTech X-Motion) that resembled a pair of glasses (see Fig. 1). When turned on, several visual components were visible through the right lens of the display (see Fig. 2). These components included (1) a Head Attitude Scale (HAS), which is a magenta-colored Cartesian graph with equal-length X-(horizontal) and Y-(vertical) axes, (2) a Pitch/Roll Indicator a tangerine-colored line with a length approximately one-third the length of the HAS horizontal and is bisected by, moves vertically along, and rotates 1269

3 (tilts) about the HAS vertical axis, and (3) a Yaw Indicator that is a tangerine-colored, open-ended, three-sided trapezoid that slides the length of the Pitch/Roll Indicator as the wearer s head is rotated left or right. The optokinetic drum for this study consisted of a synthetic composite cylinder 122 cm in height and 107 cm in diameter (see Fig. 3). The drum was suspended from a motor attached to a beam directly above the drum with four steel cables. Given the mass of the drum, and the position of the cables supporting it, this method of suspending the drum resulted in a smooth and steady rotation, free of any wobble or sway after approximately 2 seconds of rotation. Head position was maintained throughout the experiment by means of an optical chin rest in which the subject s chin rested in a stationary concave depression. Viewing took place with the subject s head centered at the axis of rotation. This resulted in a viewing distance of 48.5 cm when the subject s line of sight was perpendicular to the drum s surface. Illumination was provided by two 32-W florescent bulbs positioned directly behind a translucent plastic diffuser panel and 102 cm directly above the top of the drum. The stimulus pattern that lined the interior of the drum consisted of a black and white checkerboard pattern. Each patch was 9 high and 30 wide. Assessment Instruments MS symptoms were assessed using the Simulator Sickness Questionnaire (SSQ). 31 When scored according to published guidelines 32 the SSQ yields four scores: a total SSQ score and three subscores corresponding to nausea, oculomotor symptoms, and disorientation. Sixteen items on the questionnaire (general discomfort, fatigue, headache, eye strain, difficulty focusing, increased salivation, sweating, nausea, difficulty concentrating, fullness of the head, blurred vision, dizziness with eyes open, dizziness with eyes closed, vertigo, stomach awareness, and burping) were used to calculate SSQ scores. Subjects indicate the level at which each symptom is experienced both pretreatment and post-treatment by circling one of four choices (none, slight, moderate, or severe). Subjects were also asked to rate their overall sickness level at the conclusion of each trial using a 0 to 10 overall well-being scale (0 = I feel fine, 10 = I feel awful as if I am about to vomit). Additionally, subjects rated self-motion perception using a 0 to 10 scale (0 = I didn t feel like I was moving at all, 10 = I felt like I was rotating and the drum appeared to be totally stationary). Procedure and Design Baseline SSQ ratings were obtained at the beginning of each trial. After the subject was seated inside the drum, the seethrough display was placed on their head and adjusted for comfort and visibility. Those in the experimental condition (symbology turned on ) were probed as to whether or not the symbology was visible. The subject was then instructed to place his or her chin in the chinrest that was adjusted for height if necessary. In the experimental condition, the subject was instructed to fixate on the center of the crossshaped HAS and to maintain fixation throughout the trial. In the control condition, the subject was instructed to simply look forward at the interior of the drum as it rotated. The subject closed his/her eyes and the motor was turned on until the drum steadily rotated at a speed of 60 /s (10 rpm). Once instructed to open their eyes, drum viewing was maintained for 5 minutes. After the viewing period elapsed, the experimenter instructed the subject to close their eyes and the motor was turned off. The subject then removed the see-through display, exited the drum, and filled out the postexposure page of the SSQ. Subjects were allowed to rest until any unpleasant symptoms subsided. Each subject served in both the experimental and control conditions. Participation was completely counterbalanced to control for any possible order effects including adaptation. The subject was scheduled for a subsequent condition in 72 hours to allow for residual effects to subside from previous exposure. FIGURE 3. Exterior view of the optokinetic drum used in this study. Statistical Analysis All SSQ scores were analyzed using the Student t test for dependent measures. Given our directional hypothesis all 1270

4 FIGURE 4. Mean SSQ scores ± 1 SD for overall score and SSQ subscores for nausea, oculomotor symptoms, and disorientation. tests were one-tailed. Differences were considered be significant at an α level of RESULTS Four scores were calculated for each subject using methods and weighting factors outlined by Kennedy et al 32 : a total SSQ score and three subscores corresponding to nausea, oculomotor symptoms, and disorientation. The means obtained for all four scores are shown in Figure 4. For the experimental conditions, dependent t tests revealed significantly lower total SSQ scores [t(13) = 2.59, p = 0.012], and lower subscores corresponding to nausea [t(13) = 2.20, p = 0.024], oculomotor symptoms [t(13) = 2.63, p = 0.01], and disorientation [t(13) = 2.67, p = 0.009]. Overall (0 10) sickness ratings obtained in the experimental condition (mean = 1.14) were also significantly lower [t(13) = 2.65, p =0.01]than those obtained in the control condition (mean = 3.57). Selfmotion (0 10) perception ratings obtained in the experimental condition (mean = 5.0) were also significantly lower [t(13) = 1.81, p = 0.047] than those obtained in the control condition (mean = 6.5). DISCUSSION These results suggest that controlling eye movements using a wearable eye-worn display can alleviate MS symptoms when MS is visually induced. Specifically, the eye-worn device provides the user with portable fixation point that may prevent or reduce nystagmus eye movements. Hence, the current results are most applicable to situations that people might encounter that lead to visually induced MS, such as wide-screen films, virtual reality displays, and vehicle simulators. However, the more typical forms of MS that result from body motion relative to Earth may also be alleviated using visual symbology provided by an eye-worn device. Effect sizes were large in this study, suggesting that not only were results statistically significant but were potentially clinically significant as well. It is difficult to determine precisely why fixation helps alleviate MS symptoms in an optokinetic drum. Fixation may serve to visually enhance the vestibulo-ocular reflex, depending on the magnitude of retinal error velocity that results after the generation of vestibular eye movements. 33 These results are in agreement with those obtained in other studies in which visual fixation reduced the magnitude of MS effects or delayed their onset. 25,26 Although not directly measured, casual visual inspection of the subjects and verbal reports suggest that visual nystagmus may be reduced when a fixation point is attended to and other investigators have suggested that nystagmus could play a role in MS onset. 27,29,30. For future experiments that test portable fixation effects on MS, rigorous and precise measurements of visual nystagmus should be considered. Additional research is needed to test the effectiveness of visual fixation in alleviating MS symptoms in actual moving vehicles. Also, testing the device with head movements is a logical next step given that mobility is a benefit of the device and head movements were not allowed in the current study. In future studies eye movements should also be measured to ensure compliance with instructions to fixate on the symbology in the experimental condition but also to assess the prevalence of nystagmus. One question that needs to be answered before such devices can effectively be used in some situations such as military operations is how much attention does fixation take away from other required tasks? In this study, subjects were carefully instructed to fixate. Wearing a device like the one used in this study may or may not cause operational issues in the field depending on what tasks are required by the user. For example, such a device might work well for personnel being transported but not work well for those attending to displays, controls, and/or scenes as needed to accomplish their respective tasks. Hence, passively transported soldiers might find such a device useful but pilots, co-pilots, navigators, and other personnel may find that continually fixating on a virtual point in space is distracting and counterproductive in terms of performing their required duties. The main limitation of this study may be the artificial nature of the laboratory environment used to conduct the experiment. Subjects viewed an artificially contrived stimulus with head and body movements strictly controlled. When conditions become too far removed from real-world conditions, ecological validity becomes a concern. This is of course beneficial to strictly controlling all possible variables in that the effectiveness of independent variable in this case a device that provides for visual fixation can be rigorously assessed. However, the applicability of our results to environments that can be experienced in daily will subsequently need to be assessed. This study does not directly address the most common forms of MS such as seasickness, carsickness, and airsickness. These all entail actual movement of people relative to Earth. However, the current results do suggest that providing a wearable fixation point 1271

5 for travelers could offer MS alleviation and subsequent research should address this possibility. REFERENCES 1. Rine RM, Schubert MC, Balkany TJ: Visual-vestibular habituation and balance training for motion sickness. Phys Ther 1999; 79: Trumbull R, Chinn HI, Maag CH, et al: Effect of certain drugs on the incidence of seasickness. Clin Pharmacol Ther 1960; 1(3): Handford SW, Cone TE, Gover SC: A ship s motion and the incidence of seasickness. Mil Surg 1953; 113(3): Bruner JM: Seasickness in a destroyer escort squadron. U S Armed Forces Med J 1955; 6(4): Pethybridge RJ, Davies JW, Walters JD: A Pilot Study on the Incidence of Sea Sickness in RN Personnel on 2 Ships. INM Report 55/78, Alverstoke, Hampshire, England, Institute of Naval Medicine, Money KE: Motion sickness. Physiol Rev 1970; 50: Hixson WC, Guedry FE, Lentz JM: Results of a longitudinal study of airsickness incidence during naval flight officer training. In: Motion Sickness: Mechanism Prediction, Prevention and Treatment, Paper 30:1 13. Neuilly-sur-Seine, France, Advisory Group for Aerospace Research and Development, North Atlantic Treaty Organization, 1984;. AGARD Conference Proceedings 372. Available at dtic/tr/fulltext/u2/p pdf. (Defense Technical Information Center); accessed July 22, Dobie TG: Airsickness in Aircrew. Neuilly-sur-Seine, France, Advisory Group for Aerospace Research and Development, North Atlantic Treaty Organization, 1974; AGARD Report 177. Available at (Defense Technical Information Center); accessed July 22, Geeze DS, Pierson WP: Airsickness in B-52 crew members. Mil Med 1986; 151: Strongin TS, Charlton SG: Motion sickness in operational bomber crews. Aviat Space Environ Med 1991; 62(1): Royal L, Jessen B, Wilkins M: Motion sickness susceptibility in student navigators. Aviat Space Environ Med 1984; 55(4): Antuñano MJ, Hernandez JM: Incidence of airsickness among military parachutists. Aviat Space Environ Med 1989; 60: Kellogg RS, Gillingham KK: United States Air Force experience with simulator sickness, research and training. Proceedings 30th Annual Meeting Human Factors Society, 1986; 1: Kennedy RS, Lilienthal MG, Berbaum KS, Baltzley DR, McCauley ME: Simulator sickness in U.S. Navy flight simulators. Aviat Space Environ Med 1989; 60: Blok RJ: Simulator sickness in the Army UH-60A Blackhawk flight simulator. Mil Med 1992; 157(3): Weinstein SE, Stern RM: Comparison of marezine and dramamine in preventing symptoms of motion sickness. Aviat Space Environ Med 1997; 68: Arner O, Diamant H, Goldberg L, Wrange G: Antihistamines in seasickness. Arch Int Pharmacodyn Ther 1958; 117: Spinks A, Wasiak J: Scopolamine (hyoscine) for preventing and treating motion sickness. Cochrane Database System Review 2011; 15(6): CD Available at ( accessed July 22, Rita G, Phillips B, Lojewski R, Wang Z, Boyd J, Putcha L: The efficacy of low-dose intranasal scopolamine for motion sickness. Aviat Space Environ Med 2010; 81: Hu S, Stritzel R, Chandler A, Stern RM: P6 acupressure reduces symptoms of vection-induced motion sickness. Aviat Space Environ Med 1995; 66: Hu S, Stern RM, Koch KL: Electrical acustimulation relieves vectioninduced motion sickness. Gastroenterology 1992; 102: Miller KE, Muth ER: Efficacy of acupressure and acustimulation bands for the prevention of motion sickness. Aviat Space Environ Med 2004; 75: Warwick-Evans L, Masters J, Redstone S: A double-blind placebo controlled evaluation of acupressure in the treatment of motion sickness. Aviat Space Environ Med 1991; 62: Bruce DG, Golding JF, Hockenhull N, Pethybridge RJ: Acupressure and motion sickness. Aviat Space Environ Med 1990; 61: Stern RM, Hu S, Anderson RB, Leibowitz HW, Koch KL: The effects of fixation and restricted visual field on vection-induced motion sickness. Aviat Space Environ Med 1990; 61: Webb NA, Griffin MJ: Optokinetic stimuli: motion sickness, visual acuity, and eye movements. Aviat Space Environ Med 2002; 73: Flanagan MB, May JG, Dobie TG: Optokinetic nystagmus, vection, and motion sickness. Aviat Space Environ Med 2002; 73: Reason JT, Brand JJ: Motion sickness, pp London, Academic Press, Pola J, Wyatt HJ, Lustgarten M: Visual fixation of a target and suppression of optokinetic nystagmus: effects of varying target feedback. Vision Res 1995; 35: Ebenholtz SM, Cohen MM, Linder BJ: The possible role of nystagmus in motion sickness: a hypothesis. Aviat Space Environ Med 1994; 65: Kennedy RS, Lane NE, Berbaum KS, Lilienthal MG: Simulator sickness questionnaire: an enhanced method for quantifying simulator sickness. Int J Aviat Psychol 1993; 3: Kennedy RS, Drexler JM, Compton DE, et al: Configural scoring of simulator sickness, cybersickness, and space adaptation syndrome: similarities and differences. In: Virtual and Adaptive Environments: Applications, Implications, and Human Performance Issues, pp Edited by Hettinger LJ, Hass MW. Mahwah, NJ, Lawrence Erlbaum Associates, Leigh RJ, Huebner WP, Gordon JL: Supplementation of the human vestibulo-ocular reflex by visual fixation and smooth pursuit. J Vestib Res 1994; 4: