Ukkonen O I, Derrington A M
School of Psychology, University of Nottingham, University Park, NG7 2RD, Nottingham, UK.
Vision Res. 2000;40(24):3359-71. doi: 10.1016/s0042-6989(00)00197-8.
We used a pedestal test [Lu & Sperling (1995a). Vision Research, 35, 2697-2722] to determine whether motion discrimination of contrast-modulated gratings has different properties at low contrast (4.5%) and at high contrast (45%). The amplitude-modulated gratings consisted of a 5 c/deg static carrier modulated by a moving 1 c/deg contrast envelope. We found that when contrast is low direction discrimination for contrast-modulated gratings is vulnerable to pedestals and becomes impossible at about 4 Hz. At high contrast contrast-modulated gratings are unaffected by pedestals and modulation sensitivity in a motion direction-discrimination task remains high up to 12 Hz. These results are consistent with the hypothesis that separate mechanisms analyse motion of contrast-modulated gratings at low and at high contrast; at low contrast motion analysis is based on feature tracking, whereas at high contrast, contrast-modulated gratings are analysed by spatio-temporal filters.
我们采用了一种基座测试[Lu和Sperling（1995a）。《视觉研究》，35，2697 - 2722]来确定对比度调制光栅的运动辨别在低对比度（4.5%）和高对比度（45%）时是否具有不同特性。幅度调制光栅由一个5周/度的静态载波组成，该载波由一个移动的1周/度对比度包络调制。我们发现，当对比度较低时，对比度调制光栅的方向辨别容易受到基座的影响，并且在大约4赫兹时变得不可能。在高对比度下，对比度调制光栅不受基座影响，并且在运动方向辨别任务中的调制灵敏度在高达12赫兹时仍保持较高。这些结果与以下假设一致：在低对比度和高对比度下，分别有不同机制分析对比度调制光栅的运动；在低对比度下，运动分析基于特征跟踪，而在高对比度下，对比度调制光栅由时空滤波器进行分析。
