Crowell J A, Banks M S
Department of Psychology, University of California, Berkeley 94720-2020, USA.
Vision Res. 1996 Feb;36(3):471-90. doi: 10.1016/0042-6989(95)00121-2.
Several aspects of the viewing situation affect the ability to determine heading from optical flow. These include the amount of depth variation and number of texture elements in the scene, the location and amount of the visual field stimulated, and the position of the focus of expansion within the stimulus. Without a quantification of the discrimination information provided by the stimuli presented to the observer, it is impossible to determine how much of an observed change in performance reflects the properties of neural mechanisms and strategies employed by the observer. To enable a better quantification, we developed an ideal observer for the discrimination of heading from random-dot flow fields. Internal noises of the ideal observer were set by the results of single-dot velocity discrimination experiments. We compared human and ideal observer performance in discriminating headings with different patterns of flow (e.g. radial vs laminar) presented on different parts of the retina. Efficiency--the ratio of ideal and human thresholds--was fairly constant for the various flow patterns and retinal eccentricities. This outcome indicates that most of the variation in human observers' ability to estimate heading from the flow patterns and retinal loci considered here is due to changes in the discrimination information provided by the stimulus after measurement by the visual system. In the discussion, we show how the ideal observer can be used to quantify the spatial distribution of heading discrimination information for any observer translation through any scene represented by dots.
观察情境的几个方面会影响从光流确定方向的能力。这些方面包括场景中深度变化的量和纹理元素的数量、受刺激的视野的位置和范围，以及刺激内扩张焦点的位置。如果不对呈现给观察者的刺激所提供的辨别信息进行量化，就无法确定观察到的性能变化中有多少反映了观察者所采用的神经机制和策略的特性。为了实现更好的量化，我们开发了一种理想观察者，用于从随机点流场中辨别方向。理想观察者的内部噪声由单点速度辨别实验的结果设定。我们比较了人类观察者和理想观察者在辨别不同视网膜部位呈现的不同流模式（例如径向流与层流）方向时的表现。效率——理想阈值与人类阈值的比率——对于各种流模式和视网膜离心率来说相当恒定。这一结果表明，在此处考虑的从流模式和视网膜位置估计方向的人类观察者能力的大部分变化，是由于视觉系统测量后刺激所提供的辨别信息的变化所致。在讨论中，我们展示了理想观察者可如何用于量化任何观察者在通过由点表示的任何场景进行平移时方向辨别信息的空间分布。
