Data_Sheet_2_Postural and Head Control Given Different Environmental Contexts.docx

Virtual reality allows for testing of multisensory integration for balance using portable Head Mounted Displays (HMDs). HMDs provide head kinematics data while showing a moving scene when participants are not. Are HMDs useful to investigate postural control? We used an HMD to investigate postural sway and head kinematics changes in response to auditory and visual perturbations and whether this response varies by context. We tested 25 healthy adults, and a small sample of people with diverse monaural hearing (n = 7), or unilateral vestibular dysfunction (n = 7). Participants stood naturally on a stable force-plate and looked at 2 environments via the Oculus Rift (abstract “stars;” busy “street”) with 3 visual and auditory levels (static, “low,” “high”). We quantified medio-lateral (ML) and anterior-posterior (AP) postural sway path from the center-of-pressure data and ML, AP, pitch, yaw and roll head path from the headset. We found no difference between the different combinations of “low” and “high” visuals and sounds. We then combined all perturbations data into “dynamic” and compared it to the static level. The increase in path between “static” and “dynamic” was significantly larger in the city environment for: Postural sway ML, Head ML, AP, pitch and roll. The majority of the vestibular group moved more than controls, particularly around the head, when the scenes, especially the city, were dynamic. Several patients with monaural hearing performed similar to controls whereas others, particularly older participants, performed worse. In conclusion, responses to sensory perturbations are magnified around the head. Significant differences in performance between environments support the importance of context in sensory integration. Future studies should further investigate the sensitivity of head kinematics to diagnose vestibular disorders and the implications of aging with hearing loss to postural control. Balance assessment and rehabilitation should be conducted in different environmental contexts.

虚拟现实技术可借助便携式头戴式显示器（Head Mounted Displays，HMDs）开展平衡相关的多感官整合测试。当被试自身未产生运动时，该头戴式显示器可在呈现动态视觉场景的同时采集头部运动学数据。那么头戴式显示器是否可用于姿势控制的相关研究？本研究借助头戴式显示器，探究被试在听觉与视觉扰动下的姿势晃动及头部运动学变化，并分析该响应是否因环境背景而异。本研究共招募25名健康成年人，以及小样本的两类受试群体：7名单耳听力异常者，7名单侧前庭功能障碍者。所有被试自然站立于稳定的测力平台（force-plate）上，通过Oculus Rift观看两种环境场景：抽象‘星空’与喧闹‘街景’，并设置3级视听刺激模式：静态、‘低扰动’与‘高扰动’。本研究通过测力平台的压力中心数据，量化了被试的内侧-外侧（medio-lateral，ML）与前后（anterior-posterior，AP）方向姿势晃动路径；同时通过头戴设备采集的数据，量化了头部在ML、AP、俯仰（pitch）、偏航（yaw）与滚转（roll）方向的运动路径。研究结果显示，‘低扰动’与‘高扰动’下的各类视听组合之间未出现显著差异。随后本研究将所有扰动组数据合并为‘动态扰动’类别，并与静态刺激组进行对比。在‘街景’场景中，静态与动态扰动条件下的路径增长量在多个指标上均显著更高，包括：姿势晃动ML分量、头部ML分量、AP分量、俯仰与滚转运动。相较于健康对照组，多数单侧前庭功能障碍受试者的身体晃动幅度更大，头部运动差异尤为显著，该现象在动态街景场景中尤为突出。部分单耳听力异常受试者的表现与健康对照组相近，而其余受试者（尤其是年长受试者）的表现则较差。综上，感官扰动引发的身体响应在头部运动层面被显著放大。不同环境下的表现差异表明，环境背景在多感官整合过程中具有重要作用。未来研究可进一步探究头部运动学指标对前庭功能障碍的诊断灵敏度，以及听力损失伴随衰老对姿势控制的影响；同时，平衡评估与康复训练应在多样化的环境背景下开展。