Retinal Optic Flow During Natural Locomotion - Dataset

This is the dataset supporting the publication titled "Retinal Optic Flow During Natural Locomotion" published in PLoS Computational Biology https://doi.org/10.1371/journal.pcbi.1009575 <br>The code necessary to analyze this data is included and hosted on github at https://github.com/jonmatthis/RetinalOpticFlow_PLoS_Comp_Bio.<br>See related videos at https://doi.org/10.25452/figshare.plus.17121686<br><br><b>Author Summary<br></b>We recorded the full body kinematics and binocular gaze of humans walking through real-world natural environment and estimated visual motion (optic flow) using both computational video analysis and geometric simulation. Contrary to the established theories of the role of optic flow in the control of locomotion, we found that eye-movement-free, head-centric optic flow is highly unstable due to the complex phasic trajectory of the head during natural locomotion, rendering it an unlikely candidate for heading perception. In contrast, retina-centered optic flow consisted of a regular pattern of outflowing motion centered on the fovea. Retinal optic flow contained highly consistent patterns that specified the walker's trajectory relative to the point of fixation, which may provide powerful, retinotopic cues that may be used for the visual control of locomotion in natural environments. This examination of optic flow in real-world contexts suggest a need to re-evaluate existing theories of the role of optic flow in the visual control of action during natural behavior.<br><br><b>Abstract</b><br> We examine the structure of the visual motion projected on the retina during natural locomotion in real world environments. Bipedal gait generates a complex, rhythmic pattern of head translation and rotation in space, so without gaze stabilization mechanisms such as the vestibular-ocular-reflex (VOR) a walker's visually specified heading would vary dramatically throughout the gait cycle. The act of fixation on stable points in the environment nulls image motion at the fovea, resulting in stable patterns of outflow on the retinae centered on the point of fixation. These outflowing patterns retain a higher order structure that is informative about the stabilized trajectory of the eye through space. We measure this structure by applying the curl and divergence operations on the retinal flow velocity vector fields and found features that may be valuable for the control of locomotion. In particular, the sign and magnitude of foveal curl in retinal flow specifies the body's trajectory relative to the gaze point, while the point of maximum divergence in the retinal flow field specifies the walker's instantaneous overground velocity/momentum vector in retinotopic coordinates. Assuming that walkers can determine the body position relative to gaze direction, these time-varying retinotopic cues for the body’s momentum could provide a visual control signal for locomotion over complex terrain. In contrast, the temporal variation of the eye-movement-free, head-centered flow fields is large enough to be problematic for use in steering towards a goal. Consideration of optic flow in the context of real-world locomotion therefore suggests a re-evaluation of the role of optic flow in the control of action during natural behavior.<br>

本数据集支撑发表于《公共科学图书馆·计算生物学》（PLoS Computational Biology）的论文《自然运动过程中的视网膜光流（"Retinal Optic Flow During Natural Locomotion"）》，论文DOI：https://doi.org/10.1371/journal.pcbi.1009575。
分析该数据集所需的代码已附带，并托管于GitHub仓库：https://github.com/jonmatthis/RetinalOpticFlow_PLoS_Comp_Bio。
相关视频可通过以下链接获取：https://doi.org/10.25452/figshare.plus.17121686。

**作者摘要**
我们记录了人类在真实自然环境中行走时的全身运动学参数与双眼注视姿态，并通过计算视频分析与几何模拟两种方法估算了视觉运动（光流，optic flow）。与既有关于光流在运动控制中作用的理论相悖，我们发现：由于自然运动过程中头部存在复杂的阶段性运动轨迹，无眼动的头部中心光流极不稳定，因此该类光流不太可能作为行进方向感知的依据。与之相反，以视网膜为中心的光流呈现出以中央凹为中心的规则外流模式。视网膜光流包含高度一致的模式，可反映出行进者相对于注视点的运动轨迹，这可能为自然环境下运动的视觉控制提供强有力的视网膜拓扑线索。针对真实场景下光流的研究表明，现有关于光流在自然行为中视觉控制动作的作用理论亟待重新评估。

**摘要**
本研究探讨了真实自然环境中自然运动过程中投射在视网膜上的视觉运动结构。两足行走步态会使头部在空间中产生复杂且有节律的平移与旋转运动，因此若缺乏前庭眼反射（vestibular-ocular-reflex, VOR）这类注视稳定机制，行走者通过视觉获取的行进方向会在整个步态周期中发生剧烈变化。对环境中稳定点进行注视的行为会抵消中央凹处的图像运动，进而在以注视点为中心的视网膜上形成稳定的外流模式。这类外流模式保留了高阶结构，可反映眼睛在空间中的稳定运动轨迹。我们通过对视网膜光流速度矢量场施加旋度与散度运算来量化该结构，并发现了若干对运动控制具有潜在价值的特征。具体而言，视网膜光流中中央凹旋度的符号与幅值可反映身体相对于注视点的运动轨迹，而视网膜流场中散度最大的点则可在视网膜拓扑坐标系下表征行走者的瞬时地面速度/动量矢量。假设行走者能够确定身体相对于注视方向的位置，那么这类随时间变化的身体动量视网膜拓扑线索，可为复杂地形下的运动提供视觉控制信号。与之相反，无眼动的头部中心流场的时间变化幅度较大，难以用于向目标导航。因此，在真实运动场景下考量光流的作用，意味着需要重新评估光流在自然行为中对动作控制的角色。