Brady N, Bex P J, Fredericksen R E
Vision Research Centre, McGill University, Montreal, Quebec, Canada.
Vision Res. 1997 Jul;37(14):1873-83. doi: 10.1016/s0042-6989(97)00007-2.
We compared observers' ability to discriminate the direction of apparent motion using images which varied in their spatial characteristic; white or flat spectrum noise, and 1/f noise which has an amplitude spectrum characteristic of natural scenes. The upper spatial limit for discrimination (dmax) was measured using a two-flash random dot kinematogram (RDK), which consisted either of a pair of bandpass filtered images or of a bandpass filtered image and its broadband counterpart. Six bandpass central frequencies were used, ranging from 0.25 to 5.66 cyc/deg. Subjects could perform the direction discrimination task for all six central frequencies in both the bandpass-bandpass and bandpass-broadband sequences for the 1/f images, and dmax values were found to be approximately equal in these two conditions at all spatial scales. However, for the white noise images, direction discrimination was not possible at the lowest central frequencies in the bandpass-broadband task. These data show that information from a wide range of spatial scales is equally salient to the human motion system in images whose amplitude spectra fall as 1/f. However, for white noise images, information at the higher spatial frequencies is more salient and dominates performance in the direction discrimination task. These results are consistent with a model in which spatial frequency filters in the input lines of motion detectors have octave constant spatial frequency bandwidths and equal peak sensitivity. In line with a number of recent studies, this suggests that the spatial properties of motion sensitive cells are matched to the statistical properties of natural scenes.
我们使用空间特征各异的图像，比较了观察者辨别视在运动方向的能力；这些图像包括白色或平坦频谱噪声，以及具有自然场景幅度频谱特征的1/f噪声。使用双闪光随机点运动图（RDK）测量辨别（dmax）的上限空间频率，该运动图由一对带通滤波图像或一幅带通滤波图像及其宽带对应图像组成。使用了六个带通中心频率，范围从0.25到5.66周/度。对于1/f图像，在带通-带通和带通-宽带序列中，受试者能够在所有六个中心频率下执行方向辨别任务，并且在所有空间尺度下，这两种条件下的dmax值大致相等。然而，对于白色噪声图像，在带通-宽带任务中，最低中心频率下无法进行方向辨别。这些数据表明，在幅度频谱呈1/f下降的图像中，来自广泛空间尺度的信息对人类运动系统同样显著。然而，对于白色噪声图像，较高空间频率的信息更显著，并在方向辨别任务中主导表现。这些结果与一个模型一致，在该模型中，运动探测器输入线路中的空间频率滤波器具有倍频程恒定的空间频率带宽和相等的峰值灵敏度。与最近的一些研究一致，这表明运动敏感细胞的空间特性与自然场景的统计特性相匹配。
