Ho Cindy S, Giaschi Deborah E
Department of Psychology, University of British Columbia, Canada.
Vision Res. 2009 Jul;49(14):1814-24. doi: 10.1016/j.visres.2009.04.018. Epub 2009 Apr 22.
Maximum motion displacement (Dmax) represents the largest dot displacement in a random-dot kinematogram (RDK) at which direction of motion can be discriminated. Direction discrimination thresholds for maximum motion displacement (Dmax) are not fixed but are stimulus dependent. For first-order RDKs, Dmax is larger as dot size increases and/or dot density decreases. Dmax may be limited by the receptive field size of low-level motion detectors when the dots comprising the RDK are small and densely spaced. With RDKs of increased dot size/decreased dot density, however, Dmax exceeds the spatial limits of these detectors and is likely determined by high-level feature-matching mechanisms. Using functional MRI, we obtained greater activation in posterior occipital areas for low-level RDKs and greater activation in extra-striate occipital and parietal areas for high-level RDKs. This is the first reported neuroimaging evidence supporting proposed low-level and high-level models of motion processing for first-order random-dot stimuli.
最大运动位移（Dmax）表示随机点运动图（RDK）中能够辨别运动方向的最大点位移。最大运动位移（Dmax）的方向辨别阈值并非固定不变，而是依赖于刺激。对于一阶RDK，随着点大小增加和/或点密度降低，Dmax会更大。当构成RDK的点小且密集分布时，Dmax可能会受到低水平运动探测器感受野大小的限制。然而，对于点大小增加/点密度降低的RDK，Dmax超过了这些探测器的空间限制，并且可能由高水平特征匹配机制决定。使用功能磁共振成像，我们发现对于低水平RDK，枕叶后部区域有更大激活，而对于高水平RDK，枕叶纹外区和顶叶区域有更大激活。这是首次报道的神经影像学证据，支持了针对一阶随机点刺激提出的低水平和高水平运动处理模型。
