School of Psychology, Cardiff University, Park Place, Cardiff CF10 3AT, UK.
Curr Biol. 2010 Apr 27;20(8):757-62. doi: 10.1016/j.cub.2010.02.059. Epub 2010 Apr 15.
During smooth pursuit eye movement, observers often misperceive velocity. Pursued stimuli appear slower (Aubert-Fleishl phenomenon [1, 2]), stationary objects appear to move (Filehne illusion [3]), the perceived direction of moving objects is distorted (trajectory misperception [4]), and self-motion veers away from its true path (e.g., the slalom illusion [5]). Each illusion demonstrates that eye speed is underestimated with respect to image speed, a finding that has been taken as evidence of early sensory signals that differ in accuracy [4, 6-11]. Here we present an alternative Bayesian account, based on the idea that perceptual estimates are increasingly influenced by prior expectations as signals become more uncertain [12-15]. We show that the speeds of pursued stimuli are more difficult to discriminate than fixated stimuli. Observers are therefore less certain about motion signals encoding the speed of pursued stimuli, a finding we use to quantify the Aubert-Fleischl phenomenon based on the assumption that the prior for motion is centered on zero [16-20]. In doing so, we reveal an important property currently overlooked by Bayesian models of motion perception. Two Bayes estimates are needed at a relatively early stage in processing, one for pursued targets and one for image motion.
在平稳追踪眼动中，观察者经常会产生速度错觉。被追踪的刺激物看起来更慢（奥伯特-弗莱施尔现象[1,2]），静止的物体看起来在移动（菲莱涅尔错觉[3]），移动物体的感知方向发生扭曲（轨迹错觉[4]），而自身运动则偏离真实路径（如，障碍滑雪错觉[5]）。每个错觉都表明，相对于图像速度，眼睛速度被低估了，这一发现被认为是早期感官信号准确性不同的证据[4,6-11]。在这里，我们提出了一种基于信号变得越不确定时，知觉估计就越受先验期望影响的贝叶斯替代解释[12-15]。我们发现，被追踪的刺激物的速度比固定刺激物更难区分。因此，观察者对编码被追踪刺激物速度的运动信号的不确定性更小，我们利用这一发现来根据运动的先验假设为零的前提来量化奥伯特-弗莱施尔现象[16-20]。这样做，我们揭示了当前运动知觉贝叶斯模型忽略的一个重要特性。在处理的相对早期阶段，需要两个贝叶斯估计，一个用于被追踪的目标，一个用于图像运动。
