Cleary R
Department of Psychology, University College London, U.K.
Vision Res. 1990;30(3):463-78. doi: 10.1016/0042-6989(90)90087-2.
The apparent motion of band-pass filtered random dot kinematograms was assessed by measurements of two alternative direction discrimination performance. In the case of two-dimensional (isotropically filtered) stimuli, the results were largely independent of contrast: at Michelson contrasts of 5 and 50%, near-perfect direction discrimination was obtainable for a limited range of displacements. However for one-dimensional (grating) stimuli, apparent motion seems to be highly dependent on contrast. At 5% contrast, performance was comparable to that obtained with the two-dimensional stimuli. At 50% contrast the motion percept broke down to a large extent, with consistently poor direction discrimination being obtained. The breakdown of apparent motion is interpreted in terms of a decreased signal-to-noise ratio in the pooled response of motion detectors that are tending to contrast saturation. Here, "noise" refers to the sampling components present in any apparent motion sequence. Evidence relating to the sampling frequency of the motion sequence is presented to support the hypothesis. It is argued that the discrepancy between the results obtained with one- and two-dimensional stimuli support the idea that motion is initially encoded by orientationally tuned mechanisms.
通过测量两种交替方向辨别性能来评估带通滤波随机点运动图的表观运动。对于二维（各向同性滤波）刺激，结果在很大程度上与对比度无关：在5%和50%的迈克尔逊对比度下，对于有限范围的位移可获得近乎完美的方向辨别。然而，对于一维（光栅）刺激，表观运动似乎高度依赖于对比度。在5%对比度下，性能与二维刺激所获得的性能相当。在50%对比度下，运动感知在很大程度上瓦解，方向辨别一直很差。表观运动的瓦解被解释为趋于对比度饱和的运动探测器的汇总响应中信噪比降低。这里，“噪声”指任何表观运动序列中存在的采样成分。提出了与运动序列采样频率相关的证据来支持该假设。有人认为，一维和二维刺激所获得的结果之间的差异支持了运动最初由方向调谐机制编码的观点。
