Galvanic Vestibular Stimulation Advancements for Spatial Disorientation Training
INTRODUCTION: Spatial disorientation (SD) remains the leading contributor to Class A mishaps in the U.S. Navy, consistent with historical trends. Despite this, SD training for military aircrew is largely confined to the classroom and experiential training replicating SD illusions is limited and infrequent. Static flight simulators are most commonly used for training but offer no vestibular stimulation to the flight crew, omitting the source of vestibular-mediated SD. BACKGROUND: We first cover vestibular-mediated SD illusions which may be replicated through galvanic vestibular stimulation (GVS) in a static environment. GVS is a safe, reliable, low-cost avenue for providing vestibular sensory stimulation. We review the underlying mechanisms of GVS such as the excitement and inhibition of the afferent neurons innervating the vestibular system, particularly in the binaural bipolar electrode montage. APPLICATIONS: Two approaches for how GVS may be used to enhance SD training are examined. The first is a means for providing unreliable vestibular sensory perceptions to pilots, and the second details how GVS can be leveraged for replicating vestibular-mediated SD illusions. DISCUSSION: We recommend GVS be pursued as an enhancement to existing SD training. The ability to disorient aircrew in the safe training environment of a static flight simulator would allow for aircrew familiarization to SD, serving as an opportunity to practice life-saving checklist items to recover from SD. A repeatable training profile that could be worn by military aircrew in a static flight simulator may afford a low-cost training solution to the number one cause of fatalities in military aviation. Allred AR, Lippert AF, Wood SJ. Galvanic vestibular stimulation advancements for spatial disorientation training. Aerosp Med Hum Perform. 2024; 95(7):390–398.
Prevalence of mishaps as classified by the Aeromedical Division of the Naval Safety Command from fiscal year 2011 through Q1 of fiscal year 2023. The horizontal axis corresponds to the total number of mishaps and the vertical axis corresponds to the number of Class A mishaps. The four most prevalent categories are named and labels are provided for all categories based on the Department of Defense’s Human Factors Analysis and Classification System taxonomy.4 Categories are colored based on prevalence of Class A mishaps. Nonvisual SD (grouping SD-related categories other than visual illusions: PC5-01,02,08) is the largest contributor to Class A mishaps during the last decade (even when just considering PC08), and mishap occurrences disproportionately result in Class A mishaps compared to other mishap types.
Depiction of how GVS provides electric stimulation to the afferent neurons innervating the vestibular system (shown in purple). This is an upstream modification of the vestibular system, which leads to virtual/augmented sensations of self-motion and self-orientation perception via the cortical pathways projected through the thalamus (shown in seafoam). Because this is an upstream effect, changes to the vestibulo-ocular responses (orange pathway) and vestibulo-spinal responses (blue pathway) are also expected to occur.
A) The net stimulus evoked by GVS (purple arrow) in the binaural bipolar configuration with a left cathode and right anode current polarity. All three canal afferents on the left are equally depolarized (depicted as equivalent canal activation in blue) and all three canal afferents on the right are equally hyperpolarized (depicted as equivalent canal activation in red). The plane of the canals is depicted as circles, and each individual canal’s normal vector direction is shown in black. B) A 2D view of how a left cathode and right anode current polarity evokes a net GVS canal stimulus direction mostly in roll, with a small yaw component as estimated in the literature.40
The use of binaural bipolar GVS with the ultimate goal of influencing perception. Afferent responses from kinematic stimuli (i.e., gravity, linear acceleration, and angular velocity) are combined in some way [denoted as f(·)] with the afferent responses evoked from GVS.
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