Abstract

Our sense of balance occurs through integration of vestibular, visual, and proprioceptive signals. Conflict between these signals (e.g. in virtual reality) can create dizziness or nausea. However, in a puzzling clinical condition disabling dizziness is triggered by visual motion that is unproblematic for most people (e.g. cinema) and often without theoretical cue conflict (e.g. supermarket aisles or walking past a railing / high contrast grating). These patients also commonly experience anxiety, and sometimes even out-of-body or dissociative episodes (feeling ‘not there’). The condition is Persistent Postural Perceptual Dizziness (PPPD) and the prevailing explanation is that patients have become over-reliant on vision (‘visually dependant’) following a vestibular deficit, and are therefore destabilised by complex visual environments and motion. However, this general framework leaves many puzzles unanswered, which we have begun to address: 1) why do some people develop PPPD and some not, following similar vestibular deficit? We found a spectrum of visually-induced dizziness in the healthy population (N=2335), with 10% in the patient severity range, implying a predisposition to disabling PPPD should a vestibular deficit occur. 2) what is the nature of this predisposition? We found correlation with visual discomfort to stationary images that deviate from natural scene statistics (r= 0.46; N=1387), aligning PPPD with the visual discomfort literature; and with sensitivity and aversion in other senses (e.g. to loud noises, strong tastes; r= 0.54; N=1107), suggesting the predisposition is multisensory (it also correlates with migraine, but findings hold in non-migraineurs). 3) What does it mean to be ‘visually dependent’? We found little correlation between measures of visual dependence, raising questions about how to define and measure the purported root of PPPD symptoms. The next steps are to unpack the nature of multisensory sensitivity, and to model visual dependence using formal sensory integration frameworks.