# The Effect of Retinal Eccentricity on Visually Induced Motion Sickness and Postural Control
## 4 Discussion
This manipulation produced more motion sickness symptoms than non-oscillating radial optic flow, but, more importantly, enhanced section, resulting in mixed results, with the former corroborating, but the latter contradicting, what might be predicted by the sensory conflict theory. The manipulation's effect on postural control was also mixed, with posture being disturbed in the posterior direction but not in the anterior direction. The researchers found sensory conflict theory inadequate to account for all their findings. Similarly, (the degree of) informational conflict should be ruled out as the source of postural instability under peripheral stimulation, as observed here. Irrespective of the etiology of the present finding, it appears that the peripheral advantage of postural control is no longer maintained under more complex and dynamic visual stimulation. However, the present findings are consistent with the predictions of postural instability theory, that is, unstable posture under peripheral stimulation leading to increased motion sickness symptoms. It is important to recognize how effective the central retina was, not only in reducing the symptoms of motion sickness, but also in stabilizing posture. These findings provide sound evidence for the strategy employed by VR engineers to cope with increasing reports of motion sickness associated with VR. Participants in the current study reported that they experienced the most severe motion sickness symptoms in the peripheral vision condition, but their body swayed most under full vision (the control condition), resulting in a discrepancy between subjective ratings of motion sickness symptoms and the extent of postural perturbation. The severity of symptoms reported under the central vision and full vision conditions was indistinguishable. These results are inconsistent with what postural instability theory would predict. In the present study, VR exposure lasted only 4.17 min, a relatively short duration. This effect, taken together with the previous finding that HMDs are nauseogenic [29; 38; 39], may have contributed to this discrepant result (see also [2]). Motion sickness is known to be subject to large individual differences [1; 30; 40]. These individual differences might have confounded the between-subject design employed in the present study. With random assignment of participants to one of the three experimental groups, the possibility is negligible, but nonetheless it exists. [PERSON] et al. [29] investigated whether playing console video games via an HMD triggers motion sickness. Before analyzing the data, the authors partitioned their participants into sick and well groups. Those who discontinued playing the assigned console video game during the 50 min session, declaring that they were motion sick were allocated to the sick group, whereas those who did not declare motion sickness were allocated to the well group. In their Experiment 2, the data from nine participants qualified for further analysis. Of these nine participants, eight were assigned to the sick group and one was assigned to the well group. Interestingly, the mean total post-SSQ score of the sick group was 77.6 (SD = 25.8), whereas that of the well group was 93.5 (SD = 0). Perhaps this puzzling result can be accounted for by the fact that the SSQ is a subjective measure that assesses the severity of motion sickness symptoms felt by VR users. The same fact may account for the discrepant result observed in the present study. However, further consideration of this result is left for future research. In the present study we used only one size (10\({}^{\circ}\)) to define each visual field condition. Thus, our efforts can be understood only as a preliminary study directed at the relationship between retinal eccentricity, VIMS, and postural control. More systematic variation of the sizes of field of view, as was done by [PERSON] [41], is necessary for a better understanding of the issues addressed in this study. For that reason, caution should be exercised not to overgeneralize the present findings.