Grigo A, Lappe M
Department of Zoology and Neurobiology, Ruhr University Bochum, Germany.
J Opt Soc Am A Opt Image Sci Vis. 1999 Sep;16(9):2079-91. doi: 10.1364/josaa.16.002079.
The optic flow arising in the eyes of an observer during self-motion is influenced by the occurrence of eye movements. The determination of heading during eye movements may be based on the pattern of retinal image motion (the retinal flow) or on an additional use of an extraretinal eye-movement signal. Previous research has presented support for either of these hypotheses, depending on the movement geometry and the layout of the visual scene. A special situation in which all previous studies unequivocally have agreed that an extra-retinal signal is required occurs when the visual scene consists of a single frontoparallel plane. In this situation eye movements shift the center of expansion on the retina to a location that does not correspond to the direction of self-movement. Without extraretinal input, human observers confuse the center of expansion with their heading and show a systematical heading estimation error. We reexamined and further investigated this situation. We presented retinal flow stimuli on a large projection screen in the absence of extra-retinal input and varied stimulus size, presentation duration, and orientation of the plane. In contrast to previous studies we found that in the case of a perpendicular approach toward the plane, heading judgments can be accurate. Accurate judgments were observed when the field of view was large (90 degrees x 90 degrees) and the stimulus duration was short (< or = 0.5 s). For a small field of view or a prolonged stimulus presentation, a systematic and previously described error appeared that is related to the radial structure of the flow field and the location of the center of expansion. An oblique approach toward the plane results in an ambiguous flow field with two mathematically possible solutions for heading. In this situation, when the stimulus duration was short, subjects reported a perceived heading midway between these two solutions. For longer flow sequences, subjects again chose the center of expansion. Our results suggest a dynamical change in the analysis or interpretation of retinal flow during heading perception.
观察者在自身运动过程中眼睛产生的视觉流受到眼动的影响。眼动过程中方向的确定可能基于视网膜图像运动模式（视网膜流），也可能额外利用视网膜外眼动信号。以往的研究根据运动几何形状和视觉场景布局，对这两种假设均提供了支持。当视觉场景由单个正前平行平面组成时，所有先前的研究都明确一致认为需要视网膜外信号，这是一种特殊情况。在这种情况下，眼动会将视网膜上的膨胀中心转移到与自身运动方向不对应的位置。没有视网膜外输入时，人类观察者会将膨胀中心与他们的方向混淆，并表现出系统性的方向估计误差。我们重新审视并进一步研究了这种情况。我们在没有视网膜外输入的情况下，在大型投影屏幕上呈现视网膜流刺激，并改变刺激大小、呈现持续时间和平面方向。与先前的研究不同，我们发现，在垂直接近平面的情况下，方向判断可以是准确的。当视野较大（90度×90度）且刺激持续时间较短（≤0.5秒）时，观察到了准确的判断。对于小视野或延长的刺激呈现，会出现一种与流场的径向结构和膨胀中心位置相关的系统性且先前已描述过的误差。向平面的倾斜接近会导致一个具有两个数学上可能的方向解的模糊流场。在这种情况下，当刺激持续时间较短时，受试者报告的感知方向在这两个解的中间。对于较长的流序列，受试者再次选择了膨胀中心。我们的结果表明，在方向感知过程中，对视网膜流的分析或解释存在动态变化。
