# The Effect of Retinal Eccentricity on Visually Induced Motion Sickness and Postural Control
## 1 Introduction  
The term \"vection\" refers to the illusory sensations of self-motion in the absence of actual observer movement [1; 2] (see [3] for an overview). It is these illusions that are taken advantage of in virtual reality (VR), wherein users interact with an artificially created environment. Recent advancements in VR technology, driven primarily by the game industry, further blur the boundary between the virtual and the real. At the center of the technological advancements are head-mounted displays (HMD). Equipped with the capacity to track the motion of the user's head and deliver images in 3-dimensions (3D), these devices convey a compelling sense of immersion in the virtual environment. However, for some users, VR also can trigger drowsiness, dizziness, fatigue, pallor, sweating, stomach awareness, nausea, and disorientation akin to the symptoms commonly experienced by people reporting motion sickness. When experienced during exposure to VR, these symptoms are generally referred to as visually induced motion sickness (VIMS) (see [4] for an overview). Because visual inputs are unaccompanied by the corresponding vestibular and somatosensory inputs during VR exposure, the central nervous system receives incongruent information from different sensory channels. Sensory conflict theory contends that it is the contradictory information across various sensory channels that causes VIMS [5; 6]. Other researchers contend that the role of information lies, neither in its processing nor in its content alone, but in the service of action to accomplish an intended goal. Simultaneously, the action system explores the surrounding environment in search of requisiteinformation to facilitate attaining an intended goal [7, 8]. In this way, perception and action are coupled, thus forming a continuous loop, an insight attributed to [PERSON]. In this view, the visual information depicted on the HMD specifies a behavior different from that in which the (stationary) user wearing the HMD is engaged. In other words, the mismatch that arises in VR is not between information from different channels, but between the behavior specified by the depicted visual pattern and the current behavior the user is executing. Consider a user experiencing VR via an HMD while standing. Even when standing still, the VR user's body sways, engendering optical flow, which in turn is utilized in conjunction with the information from vestibular and proprioceptive receptors to maintain balance. The visual pattern depicted on the HMD, however, specifies illusory movement through a virtual environment, which would necessitate a very different behavior from that needed to maintain an upright stance. For certain people, the coupling between perception and action is now compromised, making the task of maintaining posture more challenging than if based on the veridical information available in the real world. Such degraded capacity to control posture is what triggers VIMS in VR and is the central tenet underlying postural instability theory [9, 10, 11]. Sensory conflict theory and postural instability theory are two prominent theories put forth to account for VIMS. Both recognize informational conflict inherent in VR as the source of VIMS, but the postural instability theory goes further to underscore the consequences of information detected on behavior, in general, and on postural control in particular. With an uneven distribution of neural receptors across its surface, the retina is thought to be divided into two distinct regions, center and periphery, whose functional roles differ. Indeed, numerous studies have been conducted to elucidate the center-periphery distinction in visual perception. [PERSON] and colleagues first addressed this issue by using circular section or rotary self-motion perception [12, 13, 14]. [PERSON] et al. [12] reported that stimulating the peripheral retina, particularly outside a 30\({}^{\circ}\) diameter area of the central visual field, can elicit self-motion perception, but stimulating the central retina cannot.