Fisher N, Zanker J M
Centre for Visual Sciences, Research School of Biological Sciences, The Australian National University, Canberra, ACT.
Perception. 2001;30(11):1321-36. doi: 10.1068/p3156.
In order to study the integration of local motion signals in the human visual system, we measured directional tuning curves for the barber-pole illusion by varying two crucial aspects of the stimulus layout independently across a wide a range in the same experiment. These were the orientation of the grating presented behind the rectangular aperture and the aspect ratio of the aperture, which in combination determine the relative contributions of local motion signals perpendicular to the gratings and parallel to the aperture borders, respectively. The strength of the illusion, ie the tendency to perceive motion along the major axis of the aperture, obviously depends on the spatial layout of the aperture, but also on grating orientation. Subjects were asked which direction they perceived and how compelling their motion percept was, revealing different strategies of the visual system to deal with the barber-pole stimulus. Some individuals respond strongly to the unambiguous motion information at the boundaries, leading to multistable percepts and multimodal distributions of responses. Others tend to report intermediate directions, apparently being less influenced by the actual boundaries. The general pattern of deviations from the motion direction perpendicular to grating orientation--a decrease with aspect ratio approaching unity (ie square-shaped apertures) and with gratings approaching parallel orientation to the shorter aperture boundary--is discussed in the context of simple phenomenological models of motion integration. The best fit between model predictions and experimental data is found for an interaction between two stimulus parameters: (i) cycle ratio, which is the sine-wave gratings equivalent of the terminator ratio for line gratings, describing the effects from the aperture boundaries, and (ii) the grating orientation, responsible for perpendicular motion components, which describes the influence of motion signals from inside the aperture. This suggests that the most simple cycle (terminator) ratio explanation cannot fully account for the quantitative properties of the barber-pole illusion.
为了研究人类视觉系统中局部运动信号的整合，我们在同一实验中，通过在很宽的范围内独立改变刺激布局的两个关键方面，测量了理发店旋转柱体错觉的方向调谐曲线。这两个方面分别是矩形孔径后面呈现的光栅的方向以及孔径的长宽比，它们共同决定了垂直于光栅和平行于孔径边界的局部运动信号的相对贡献。错觉的强度，即沿孔径主轴感知运动的倾向，显然不仅取决于孔径的空间布局，还取决于光栅方向。我们询问受试者他们感知到的方向以及他们的运动感知有多强烈，从而揭示了视觉系统处理理发店旋转柱体刺激的不同策略。一些个体对边界处明确的运动信息反应强烈，导致多稳态感知和反应的多峰分布。另一些人则倾向于报告中间方向，显然受实际边界的影响较小。我们在简单的运动整合现象学模型的背景下，讨论了与垂直于光栅方向的运动方向的偏差的一般模式——随着长宽比接近1（即方形孔径）以及光栅接近与较短孔径边界平行的方向，偏差减小。在两个刺激参数之间的相互作用中，我们发现模型预测与实验数据之间的最佳拟合：（i）周期比，它是线光栅的终止比的正弦波光栅等效物，描述了孔径边界的影响；（ii）光栅方向，负责垂直运动分量，描述了孔径内部运动信号的影响。这表明最简单的周期（终止）比解释不能完全解释理发店旋转柱体错觉的定量特性。
