## 5 Discussion  
A summary of the proposed human study is that twenty-four young healthy individuals, aged 18-35 years, with no neurological, musculoskeletal, or balance issues, will be recruited and randomly placed into two groups for this crossover design study. Using the VR headset, group one will receive six days of training by performing rhythmic horizontal headshake activities via a visual feedback protocol while performing simultaneous weight shift training standing on a floor surface or on an Airex foam pad. Meanwhile, group two will perform no training for six days and the order will be reversed. Six pre- and post-assessments of VOR gain, eye movements, electromyography and balance will be collected at specific periods. A two-intervention (training vs. no-training) by six-time-points repeated measures ANOVA will be used to analyze data. Significance will be set at \(\alpha\leq 0.05\). Post hoc tests will be conducted using a combination of paired \(t\)-tests with Bonferroni adjustments. The overarching goal of this endeavor is that VR will be an effective means to deliver the Concurrent HS-WST comparable to the protocol of the NeuroCom(r) as indicated by enhancement in vestibuloocular and -motor responses. We expect that the effect of the novel training will significantly recalibrate VOR gains and decrease eye movement variability to maintain gaze stabilization (Figure 4). The vestibuloocular recalibration and decreased eye movement variability will be due to the repeated, rhythmic headshake motions which will activate the SCCs and otolith organs to transit impulses through the vestibulocchlear nerve to the vestibular nerve at the lateral pontomedullary junction. Through mediating pathways including the abducens nucleus, medial longitudinal fasciculus, and oculomotor nuclei, specific extraocular muscles are driven to produce compensatory eye movements leading to gaze stabilization for postural stability [11; 34]. Evidence of the gaze stabilization will be shown by the decreased eye movement variability. The recalibration of the VOR gain would likely be in the down-gain direction [16] following simultaneous enhancement and suppression of vestibular signals and eye movement signals via long-term potentiation (LTP) and depression (LTD), respectively, as the underlying mechanism [11]. We also anticipate that postural balance will be improved by reweighting the somatosensory ratio to compensate for the changes in the other sensory channels. The influence on the somatosensory system will mainly be due to the stimulation of proprioceptors in the soles of the feet and in the joints of the lower limbs during the WST. This will result in a bottom-up signal transmission, will modify spinal reflexes, and the somatosensory input which will be integrated in the CNS together with the vestibular and visual inputs to produce a more efficient postural response [34; 35]. Our novel VR vestibular training is hypothesized to finetune postural muscle activation patterns by decreasing EMG amplitude signals, as less neural activity is required to produce the amount of force production for balance control (Figure 5) [16]. The modulation of the muscle activation would be suggestive of refined descending vestibular impulses following the activation of the semicircular canals [16]. Figure 4: Horizontal eye movement. Representative data of the horizontal eye movements of a participant performing balance assessment on the force plate perturbation device. S1 = pre-assessment, S2 = post-assessment. Consequently, the training will lead to improved postural flexibility and shortened automatic postural response time through modulating of the descending vestibular responses as expected to be shown during the perturbation trial assessments (Figure 6) [16]. The improved postural flexibility is hypothesized to stem from an increased COP sway velocity variability which could indicate more flexibility as participants exhibit larger but optimal limits stability for balance control [36].