Ledgeway Timothy, Hutchinson Claire V
School of Psychology, University of Nottingham, University Park NG7 2RD, UK.
Vision Res. 2006 Feb;46(4):556-67. doi: 10.1016/j.visres.2005.07.008. Epub 2005 Aug 15.
Previous psychophysical studies (e.g., Smith & Ledgeway, 1997) have provided evidence that under some conditions, the detection of a particular class of stimuli (contrast-modulated static noise) widely employed to study second-order motion processing may be inadvertently based on encoding local imbalances in luminance motion energy. In particular when static noise composed of relatively large noise elements is used, direction-identification performance at threshold may actually be mediated by the same mechanisms that respond to first-order motion, due to the presence of persistent spatial clusters of noise elements of the same polarity. However, Benton and Johnson (1997) modeled the responses of conventional motion-energy detectors to contrast-modulated static noise patterns and found no evidence of any systematic directional biases in such stimuli when the mean opponent motion energy was used to quantify performance. In the present paper we sought to resolve this discrepancy and show that the precise manner in which computational models are implemented is crucial in determining their response to contrast-modulated, second-order motion patterns. In particular we demonstrate that by considering the information encapsulated by the peak (rather than the mean) opponent motion energy and the predominantly local nature of imbalances in motion energy that can arise in contrast-modulated static noise, it is possible to readily model the patterns of empirical results found.
以往的心理物理学研究（例如，Smith和Ledgeway，1997）已经提供了证据，表明在某些条件下，用于研究二阶运动处理的一类广泛使用的特定刺激（对比度调制的静态噪声）的检测可能无意中基于对亮度运动能量中的局部不平衡进行编码。特别是当使用由相对较大的噪声元素组成的静态噪声时，由于存在相同极性的噪声元素的持续空间簇，阈值处的方向识别性能实际上可能由对一阶运动做出反应的相同机制介导。然而，Benton和Johnson（1997）对传统运动能量探测器对对比度调制的静态噪声模式的反应进行了建模，发现当使用平均对立运动能量来量化性能时，在这种刺激中没有任何系统方向偏差的证据。在本文中，我们试图解决这一差异，并表明计算模型的实现方式在确定其对对比度调制的二阶运动模式的反应方面至关重要。特别是我们证明，通过考虑峰值（而不是平均值）对立运动能量所封装的信息以及对比度调制的静态噪声中可能出现的运动能量不平衡的主要局部性质，可以很容易地对所发现的实证结果模式进行建模。
