Magnussen Camilla M, Orbach Harry S, Loffler Gunter
Department of Life Sciences, Glasgow Caledonian University, Cowcaddens Road, Glasgow G4 0BA, UK.
Vision Res. 2013 Oct 18;91:21-35. doi: 10.1016/j.visres.2013.07.014. Epub 2013 Jul 31.
Judging the motion of objects is a fundamental task that the visual system executes in everyday life in order for us to navigate and interact safely with our surroundings. A number of strategies have been suggested to explain how the visual system uses motion information from different points of an object to compute veridical directions of motion. These include combining ambiguous signals from object contours via a vector summation (VS) or intersection of constraints (IOC) calculation, pooling information using a maximum likelihood or tracking object features. We measured the perceived direction of motion for a range of cross-shaped stimuli (composed of two superimposed lines) to test how accurately humans perceive their motion and compared data to predictions from these strategies. Crosses of different shapes (defined by the angle between the component lines) translated along 16 directions of motion with constant speed. The crosses either moved along one of their symmetry axes (balanced conditions with line components equidistant to the direction of motion) or had their symmetry axis tilted relative to the motion (unbalanced conditions) Data show reproducible differences between observers, including occasional bimodal behaviour, and exhibit the following common patterns. There is a general dependence on direction of motion: For all conditions, when motion is along cardinal axes (horizontal and vertical), perception is largely veridical. For non-cardinal directions, biases are typically small (<10 deg) when crosses are balanced but large biases occur (≥30 deg) when crosses are tilted relative to their direction of motion. Factors influencing the pattern of biases are the shape and tilt of the cross as well as the proximity of its direction of motion to cardinal axes. The dependence of the biases on the direction of motion is inconsistent with any isotropic mechanisms including VS, IOC, maximum likelihood or feature tracking. Instead, perception is biased by a number of intrinsic properties of the cross and external references. The strength of these cues depends on the type, with elongation producing the strongest weight, and their proximity to the direction of motion. This suggests that the visual system may rely on a number of static cues to improve the known low precision for non-cardinal directions of motion, a process which can, however, result in large perceptual biases in certain circumstances.
判断物体的运动是视觉系统在日常生活中执行的一项基本任务，以便我们能够安全地在周围环境中导航和互动。人们提出了许多策略来解释视觉系统如何利用来自物体不同点的运动信息来计算真实的运动方向。这些策略包括通过向量求和（VS）或约束交集（IOC）计算来组合来自物体轮廓的模糊信号、使用最大似然法合并信息或跟踪物体特征。我们测量了一系列十字形刺激（由两条叠加线组成）的运动感知方向，以测试人类对其运动的感知有多准确，并将数据与这些策略的预测进行比较。不同形状（由组成线之间的角度定义）的十字以恒定速度沿16个运动方向平移。十字要么沿着其对称轴之一移动（线分量与运动方向等距的平衡条件），要么其对称轴相对于运动倾斜（不平衡条件）。数据显示观察者之间存在可重复的差异，包括偶尔的双峰行为，并呈现出以下常见模式。对运动方向存在普遍依赖性：在所有条件下，当运动沿着基本轴（水平和垂直）时，感知在很大程度上是真实的。对于非基本方向，当十字平衡时偏差通常较小（<10度），但当十字相对于其运动方向倾斜时会出现较大偏差（≥30度）。影响偏差模式的因素包括十字的形状和倾斜度以及其运动方向与基本轴的接近程度。偏差对运动方向的依赖性与任何各向同性机制（包括VS、IOC、最大似然法或特征跟踪）不一致。相反，感知受到十字的一些固有属性和外部参考的影响。这些线索的强度取决于类型，伸长产生最强的权重，以及它们与运动方向的接近程度。这表明视觉系统可能依赖于一些静态线索来提高已知的非基本运动方向的低精度，然而，这一过程在某些情况下可能会导致较大的感知偏差。
