To calibrate stereoscopic depth from disparity our visual system must compensate for an object’s egocentric location. Ideally, the perceived three-dimensional shape and size of objects in visual space should be invariant with their location such that rigid objects have a consistent identity and shape. These percepts should be accurate enough to support both perceptual judgments and visually-guided interaction. This theoretical note reviews the relationship of stereoscopic depth constancy to the geometry of stereoscopic space and seemingly esoteric concepts like the horopter. We argue that to encompass the full scope of stereoscopic depth constancy, researchers need to consider not just distance but also direction, that is 3D egocentric location in space. Judgements of surface orientation need to take into account the shape of the horopter and the computation of metric depth (when tasks depend on it) must compensate for direction as well as distance to calibrate disparities. We show that the concept of the horopter underlies these considerations and that the relationship between depth constancy and the horopter should be more explicit in the literature.

为了从视差校准立体深度，我们的视觉系统必须补偿对象的自我中心位置。理想情况下，视觉空间中物体的感知三维形状和大小应与其位置保持不变，从而使刚性物体具有一致的身份和形状。这些感知应该足够准确，以支持感知判断和视觉引导交互。这篇理论笔记回顾了立体深度恒常性与立体空间的几何形状和看似深奥的概念（如 horopter）之间的关系。我们认为，要涵盖立体深度恒定性的全部范围，研究人员不仅需要考虑距离，还需要考虑方向，即空间中的 3D 以自我为中心的位置。表面方向的判断需要考虑 horopter 的形状，并且公制深度的计算（当任务取决于它时）必须补偿方向和距离以校准差异。我们表明，horopter 的概念是这些考虑的基础，并且深度恒定性和 horopter 之间的关系应该在文献中更加明确。