# The Effect of Retinal Eccentricity on Visually Induced Motion Sickness and Postural Control
## 4 Discussion  
The present study attempted to elucidate the seemingly conflicting findings reported in the literature on the relationship between retinal eccentricity, VIMS, and postural control. In particular, we sought to clarify (in a more dynamic VR environment) whether peripheral stimulation produces, not only more severe symptoms of motion sickness, but also more unstable posture than central stimulation. Wearing an HMD masked for the central 10\({}^{\circ}\) (peripheral vision), the peripheral except for the central 10\({}^{\circ}\) (central vision), or unmasked (control), participants watched _The Great Wall_, a 3D VR application conveying self-movement along China's Great Wall while in a rocket-powered rickshaw. SSQ was administered to assess VIMS symptoms before and after VR exposure. In addition, postural sway data were collected using a wireless motion tracking system with sensors attached to participants' heads, torsos, and hips. Although no participant reported any symptoms prior to the experiment (pre-SSQ scores for the three groups were 1.87 (peripheral vision), 0.94 (central vision), and 2.18 (control), respectively), all three experimental conditions produced and/or enhanced motion sickness symptoms after VR exposure. Peripheral vision provoked the most severe motion sickness symptoms, not only in the total score, but also in the three SSQ sub-scores (Figure 1). In contrast, full vision (the control condition) most perturbed posture, particularly in the AP direction (Figure 2). The effects of VR exposure were weakest for both subjective assessment of motion sickness and postural disturbance under central vision. Finding that the retinal periphery enhances motion sickness symptoms is consistent with the general consensus held in the VR community [18; 19; 20] wherein its practitioners reduce the field of view in an attempt to lessen motion sickness symptoms. In the current study, reported symptom severity was greater with full vision than central vision. Because the retinal periphery was stimulated in both peripheral vision and full vision conditions, it appears that the retinal periphery is more susceptible to VIMS. This result corroborates the contention that the retinal periphery facilitates section [12; 13; 34] and that section is a prerequisite for VIMS [1; 10]. Postural sway increased more with full vision than with peripheral vision. Central vision induced the least disturbance, particularly in the AP direction. [PERSON] and [PERSON] [27], in their critical review investigating the relationship of field of view and postural control, confirmed that the majority of the 12 studies identified peripheral vision as dominant in postural control, stabilizing posture when individuals are subjected to section. This conclusion was true irrespective of the various sizes of central and peripheral visual fields defined in the studies, and also irrespective of the different hardware systems employed to produce section (e.g., desktop display, projection screen, HMD), and more. Given this robust finding, we suspected that the peripheral advantage of postural control reported in the literature may have been due to the use of relatively simple visual patterns (e.g., linear translation, circular rotation, or random dots that remained stationary) to induce section. Although it is not clear how the retinal periphery resolves the informational conflict inherent in section illusions to effect postural control, this ability is no longer preserved under more complex visual stimulation. It may be that increased conflict of information from different sensory channels produced the current results. In our study, participants standing upright experienced section depicting two-dimensional motion (i.e., forward locomotion along a rugged path). [PERSON] and colleagues increased sensory conflict in their radial optic flow displays by adding jitter, i.e., viewpoint oscillation [35; 36] (see [37] for an overview).