Braun Doris I, Schütz Alexander C, Gegenfurtner Karl R
Justus-Liebig-University Giessen, Abteilung Allgemeine Psychologie, Otto-Behaghel-Str. 10F, D-35394 Giessen, Germany.
Vision Res. 2010 Dec;50(24):2740-9. doi: 10.1016/j.visres.2010.07.028. Epub 2010 Aug 13.
The visual system can detect speed changes of moving objects only by means of alterations of retinal image motion, which is also subject to changes induced by head or eye movements. Here we investigated whether smooth pursuit eye movements affect the ability to localize short speed perturbations of large context stimuli. Psychophysical thresholds for localization, discrimination and detection of speed perturbations in one of two context stimuli were measured under two main conditions: in fixation trials subjects fixated a central stationary spot, in pursuit trials they followed a horizontally moving target with their eyes. Context stimuli were vertically oriented sine wave gratings moving simultaneously above and below the fixation or pursuit target for one second in the same direction at the same or a different speed as the pursuit target. During the movement one of the gratings suddenly changed its speed for 500 ms and returned to its original speed. Observers were asked to discern the location of the speed change (two-alternative spatial forced choice task). While detection (two-interval forced choice) and discrimination thresholds for the kind of speed perturbation were in the normal range of Weber fractions of 10-15%, thresholds for the location of the speed perturbation were dramatically increased to 30-50%. Localization thresholds were particularly high when the retinal motion was mainly due to the context movements as during fixation or slow pursuit and significantly reduced when the retinal motion was mainly due to pursuit. This result indicates that the origin of retinal motion, whether it is caused by object motion or by voluntary pursuit is important. We conclude that the localization of speed perturbations affecting one of two peripheral moving objects is exceedingly complicated for the visual system probably due to the dominance of relative motion. During smooth pursuit the ability to localize speed perturbations of non-foveated objects seems to be improved by additional information gained from pursuit such as corollary discharge.
视觉系统只能通过视网膜图像运动的变化来检测移动物体的速度变化，而视网膜图像运动也会因头部或眼睛运动而发生变化。在这里，我们研究了平稳跟踪眼球运动是否会影响对大背景刺激中短时间速度扰动的定位能力。在两种主要条件下测量了对两种背景刺激之一中速度扰动的定位、辨别和检测的心理物理学阈值：在注视试验中，受试者注视中央静止点；在跟踪试验中，他们用眼睛跟踪水平移动的目标。背景刺激是垂直定向的正弦波光栅，在注视或跟踪目标上方和下方同时以与跟踪目标相同或不同的速度沿相同方向移动一秒钟。在运动过程中，其中一个光栅突然改变其速度500毫秒，然后恢复到原来的速度。要求观察者辨别速度变化的位置（二选一空间强制选择任务）。虽然速度扰动类型的检测（二间隔强制选择）和辨别阈值在韦伯分数10 - 15%的正常范围内，但速度扰动位置的阈值却大幅提高到30 - 50%。当视网膜运动主要由背景运动引起时，如在注视或缓慢跟踪期间，定位阈值特别高；而当视网膜运动主要由跟踪引起时，定位阈值则显著降低。这一结果表明，视网膜运动的起源，无论是由物体运动还是由自主跟踪引起，都很重要。我们得出结论，对于视觉系统来说，定位影响两个周边移动物体之一的速度扰动极其复杂，这可能是由于相对运动的主导作用。在平稳跟踪过程中，对非中央凹物体速度扰动的定位能力似乎因从跟踪中获得的额外信息（如伴随放电）而得到改善。
