Butzer F, Ilg U J, Zanker J M
Sektion für Visuelle Sensomotorik, Neurologische Universitätsklinik, Tübingen, Germany.
Exp Brain Res. 1997 Jun;115(1):61-70. doi: 10.1007/pl00005686.
The perception of the displacement of luminance-defined contours (i.e., first-order motion) is an important and well-examined function of the visual system. It can be explained, for example, by the operation of elementary motion detectors (EMDs), which cross-correlate the spatiotemporal luminance distribution. More recent studies using second-order motion stimuli, i.e., shifts of the distribution of features such as contrast, texture, flicker, or motion, extended classic concepts of motion perception by including nonlinear or hierarchical processing in the EMD. Smooth-pursuit eye movements can be used as a direct behavioral probe for motion processing. The ability of the visual system to extract motion signals from the spatiotemporal changes of the retinal image can be addressed by analyzing the elicited eye movements. We measured the eye movement response to moving objects defined by two different types of first-order motion and two different types of second-order motion. Our results clearly showed that the direction of smooth-pursuit eye movements was always determined by the direction of object motion. In particular, in the case of second-order motion stimuli, smooth-pursuit did not follow the retinal image motion. The latency of the initial saccades during pursuit of second-order stimuli was slightly but significantly increased, compared with the latency of saccades elicited by first-order motion. The processing of second-order motion in the peripheral visual field was less exact than the processing of first-order motion in the peripheral field. Steady state smooth-pursuit eye speed did not reflect the velocity of second-order motion as precisely as that of first-order motion, and the resulting retinal error was compensated by saccades. Interestingly, for slow second-order stimuli we observed that the eye could move faster than the target, leading to small, corrective saccades in the opposite direction to the ongoing smooth-pursuit eye movement. We conclude from our results that both visual perception and the control of smooth-pursuit eye movements have access to processing mechanisms extracting first- and second-order motion.
对亮度定义轮廓的位移（即一阶运动）的感知是视觉系统一项重要且经过充分研究的功能。例如，它可以通过基本运动检测器（EMD）的运作来解释，这些检测器对时空亮度分布进行互相关运算。最近使用二阶运动刺激的研究，即对比度、纹理、闪烁或运动等特征分布的变化，通过在EMD中纳入非线性或分层处理，扩展了运动感知的经典概念。平稳跟踪眼球运动可作为运动处理的直接行为探针。通过分析引发的眼球运动，可以研究视觉系统从视网膜图像的时空变化中提取运动信号的能力。我们测量了对由两种不同类型的一阶运动和两种不同类型的二阶运动定义的移动物体的眼球运动反应。我们的结果清楚地表明，平稳跟踪眼球运动的方向始终由物体运动的方向决定。特别是，在二阶运动刺激的情况下，平稳跟踪并不跟随视网膜图像运动。与一阶运动引发的扫视潜伏期相比，跟踪二阶刺激时初始扫视的潜伏期略有但显著增加。外周视野中二阶运动的处理不如外周视野中一阶运动的处理精确。平稳跟踪眼球的稳态速度不像一阶运动那样精确地反映二阶运动的速度，由此产生的视网膜误差通过扫视来补偿。有趣的是，对于缓慢的二阶刺激，我们观察到眼球可以比目标移动得更快，从而导致与正在进行的平稳跟踪眼球运动方向相反的小的校正性扫视。我们从结果中得出结论，视觉感知和平稳跟踪眼球运动的控制都可以利用提取一阶和二阶运动的处理机制。
